function of a literature review

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What is the Purpose of a Literature Review?

4-minute read

• 23rd October 2023

If you’re writing a research paper or dissertation , then you’ll most likely need to include a comprehensive literature review . In this post, we’ll review the purpose of literature reviews, why they are so significant, and the specific elements to include in one. Literature reviews can:

1. Provide a foundation for current research.

2. Define key concepts and theories.

3. Demonstrate critical evaluation.

4. Show how research and methodologies have evolved.

5. Identify gaps in existing research.

6. Support your argument.

Keep reading to enter the exciting world of literature reviews!

What is a Literature Review?

A literature review is a critical summary and evaluation of the existing research (e.g., academic journal articles and books) on a specific topic. It is typically included as a separate section or chapter of a research paper or dissertation, serving as a contextual framework for a study. Literature reviews can vary in length depending on the subject and nature of the study, with most being about equal length to other sections or chapters included in the paper. Essentially, the literature review highlights previous studies in the context of your research and summarizes your insights in a structured, organized format. Next, let’s look at the overall purpose of a literature review.

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Literature reviews are considered an integral part of research across most academic subjects and fields. The primary purpose of a literature review in your study is to:

Provide a Foundation for Current Research

Since the literature review provides a comprehensive evaluation of the existing research, it serves as a solid foundation for your current study. It’s a way to contextualize your work and show how your research fits into the broader landscape of your specific area of study.  

Define Key Concepts and Theories

The literature review highlights the central theories and concepts that have arisen from previous research on your chosen topic. It gives your readers a more thorough understanding of the background of your study and why your research is particularly significant .

Demonstrate Critical Evaluation 

A comprehensive literature review shows your ability to critically analyze and evaluate a broad range of source material. And since you’re considering and acknowledging the contribution of key scholars alongside your own, it establishes your own credibility and knowledge.

Show How Research and Methodologies Have Evolved

Another purpose of literature reviews is to provide a historical perspective and demonstrate how research and methodologies have changed over time, especially as data collection methods and technology have advanced. And studying past methodologies allows you, as the researcher, to understand what did and did not work and apply that knowledge to your own research.  

Identify Gaps in Existing Research

Besides discussing current research and methodologies, the literature review should also address areas that are lacking in the existing literature. This helps further demonstrate the relevance of your own research by explaining why your study is necessary to fill the gaps.

Support Your Argument

A good literature review should provide evidence that supports your research questions and hypothesis. For example, your study may show that your research supports existing theories or builds on them in some way. Referencing previous related studies shows your work is grounded in established research and will ultimately be a contribution to the field.  

Literature Review Editing Services 

Ensure your literature review is polished and ready for submission by having it professionally proofread and edited by our expert team. Our literature review editing services will help your research stand out and make an impact. Not convinced yet? Send in your free sample today and see for yourself! 

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Literature reviews: functions, types and methods

Related media.

When we think of a literature review, we often forget to consider the different types of reviews and the different roles or functions that literature reviews can have.

In this short presentation I will first discuss some functions of literature reviews, and then make some points about how the function or purpose of your review should inform the type that you choose to do, and the methods that you employ.

• University of Texas Libraries

Literature Reviews

• What is a literature review?
• Steps in the Literature Review Process
• Define your research question
• Determine inclusion and exclusion criteria
• Choose databases and search
• Review Results
• Synthesize Results
• Analyze Results
• Librarian Support

What is a Literature Review?

A literature or narrative review is a comprehensive review and analysis of the published literature on a specific topic or research question. The literature that is reviewed contains: books, articles, academic articles, conference proceedings, association papers, and dissertations. It contains the most pertinent studies and points to important past and current research and practices. It provides background and context, and shows how your research will contribute to the field. 

A literature review should: 

• Provide a comprehensive and updated review of the literature;
• Explain why this review has taken place;
• Articulate a position or hypothesis;
• Acknowledge and account for conflicting and corroborating points of view

From  S age Research Methods

Purpose of a Literature Review

A literature review can be written as an introduction to a study to:

• Demonstrate how a study fills a gap in research
• Compare a study with other research that's been done

Or it can be a separate work (a research article on its own) which:

• Organizes or describes a topic
• Describes variables within a particular issue/problem

Limitations of a Literature Review

Some of the limitations of a literature review are:

• It's a snapshot in time. Unlike other reviews, this one has beginning, a middle and an end. There may be future developments that could make your work less relevant.
• It may be too focused. Some niche studies may miss the bigger picture.
• It can be difficult to be comprehensive. There is no way to make sure all the literature on a topic was considered.
• It is easy to be biased if you stick to top tier journals. There may be other places where people are publishing exemplary research. Look to open access publications and conferences to reflect a more inclusive collection. Also, make sure to include opposing views (and not just supporting evidence).

Source: Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal, vol. 26, no. 2, June 2009, pp. 91–108. Wiley Online Library, doi:10.1111/j.1471-1842.2009.00848.x.

Meryl Brodsky : Communication and Information Studies

Hannah Chapman Tripp : Biology, Neuroscience

Carolyn Cunningham : Human Development & Family Sciences, Psychology, Sociology

Larayne Dallas : Engineering

Janelle Hedstrom : Special Education, Curriculum & Instruction, Ed Leadership & Policy ​

Susan Macicak : Linguistics

Imelda Vetter : Dell Medical School

For help in other subject areas, please see the guide to library specialists by subject .

Periodically, UT Libraries runs a workshop covering the basics and library support for literature reviews. While we try to offer these once per academic year, we find providing the recording to be helpful to community members who have missed the session. Following is the most recent recording of the workshop, Conducting a Literature Review. To view the recording, a UT login is required.

• October 26, 2022 recording
• Last Updated: Oct 26, 2022 2:49 PM
• URL: https://guides.lib.utexas.edu/literaturereviews

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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

• UConn Library
• Literature Review: The What, Why and How-to Guide
• Introduction

Literature Review: The What, Why and How-to Guide — Introduction

• Getting Started
• How to Pick a Topic
• Strategies to Find Sources
• Evaluating Sources & Lit. Reviews
• Tips for Writing Literature Reviews
• Writing Literature Review: Useful Sites
• Citation Resources
• Other Academic Writings

What are Literature Reviews?

So, what is a literature review? "A literature review is an account of what has been published on a topic by accredited scholars and researchers. In writing the literature review, your purpose is to convey to your reader what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are. As a piece of writing, the literature review must be defined by a guiding concept (e.g., your research objective, the problem or issue you are discussing, or your argumentative thesis). It is not just a descriptive list of the material available, or a set of summaries." Taylor, D.  The literature review: A few tips on conducting it . University of Toronto Health Sciences Writing Centre.

Goals of Literature Reviews

What are the goals of creating a Literature Review?  A literature could be written to accomplish different aims:

• To develop a theory or evaluate an existing theory
• To summarize the historical or existing state of a research topic
• Identify a problem in a field of research 

Baumeister, R. F., & Leary, M. R. (1997). Writing narrative literature reviews .  Review of General Psychology , 1 (3), 311-320.

What kinds of sources require a Literature Review?

• A research paper assigned in a course
• A thesis or dissertation
• A grant proposal
• An article intended for publication in a journal

All these instances require you to collect what has been written about your research topic so that you can demonstrate how your own research sheds new light on the topic.

Types of Literature Reviews

What kinds of literature reviews are written?

Narrative review: The purpose of this type of review is to describe the current state of the research on a specific topic/research and to offer a critical analysis of the literature reviewed. Studies are grouped by research/theoretical categories, and themes and trends, strengths and weakness, and gaps are identified. The review ends with a conclusion section which summarizes the findings regarding the state of the research of the specific study, the gaps identify and if applicable, explains how the author's research will address gaps identify in the review and expand the knowledge on the topic reviewed.

• Example : Predictors and Outcomes of U.S. Quality Maternity Leave: A Review and Conceptual Framework:  10.1177/08948453211037398  

Systematic review : "The authors of a systematic review use a specific procedure to search the research literature, select the studies to include in their review, and critically evaluate the studies they find." (p. 139). Nelson, L. K. (2013). Research in Communication Sciences and Disorders . Plural Publishing.

• Example : The effect of leave policies on increasing fertility: a systematic review:  10.1057/s41599-022-01270-w

Meta-analysis : "Meta-analysis is a method of reviewing research findings in a quantitative fashion by transforming the data from individual studies into what is called an effect size and then pooling and analyzing this information. The basic goal in meta-analysis is to explain why different outcomes have occurred in different studies." (p. 197). Roberts, M. C., & Ilardi, S. S. (2003). Handbook of Research Methods in Clinical Psychology . Blackwell Publishing.

• Example : Employment Instability and Fertility in Europe: A Meta-Analysis:  10.1215/00703370-9164737

Meta-synthesis : "Qualitative meta-synthesis is a type of qualitative study that uses as data the findings from other qualitative studies linked by the same or related topic." (p.312). Zimmer, L. (2006). Qualitative meta-synthesis: A question of dialoguing with texts .  Journal of Advanced Nursing , 53 (3), 311-318.

• Example : Women’s perspectives on career successes and barriers: A qualitative meta-synthesis:  10.1177/05390184221113735

Literature Reviews in the Health Sciences

• UConn Health subject guide on systematic reviews Explanation of the different review types used in health sciences literature as well as tools to help you find the right review type
• << Previous: Getting Started
• Next: How to Pick a Topic >>
• Last Updated: Sep 21, 2022 2:16 PM
• URL: https://guides.lib.uconn.edu/literaturereview

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What is a literature review?

A literature review is a critical analysis of the literature related to your research topic. It evaluates and critiques the literature to establish a theoretical framework for your research topic and/or identify a gap in the existing research that your research will address.

A literature review is not a summary of the literature. You need to engage deeply and critically with the literature. Your literature review should show your understanding of the literature related to your research topic and lead to presenting a rationale for your research.

A literature review focuses on:

• the context of the topic
• key concepts, ideas, theories and methodologies
• key researchers, texts and seminal works
• major issues and debates
• identifying conflicting evidence
• the main questions that have been asked around the topic
• the organisation of knowledge on the topic
• definitions, particularly those that are contested
• showing how your research will advance scholarly knowledge (generally referred to as identifying the ‘gap’).

This module will guide you through the functions of a literature review; the typical process of conducting a literature review (including searching for literature and taking notes); structuring your literature review within your thesis and organising its internal ideas; and styling the language of your literature review.

The purposes of a literature review

A literature review serves two main purposes:

1) To show awareness of the present state of knowledge in a particular field, including:

• seminal authors
• the main empirical research
• theoretical positions
• controversies
• breakthroughs as well as links to other related areas of knowledge.

2) To provide a foundation for the author’s research. To do that, the literature review needs to:

• help the researcher define a hypothesis or a research question, and how answering the question will contribute to the body of knowledge;
• provide a rationale for investigating the problem and the selected methodology;
• provide a particular theoretical lens, support the argument, or identify gaps.

Before you engage further with this module, try the quiz below to see how much you already know about literature reviews.

Research and Writing Skills for Academic and Graduate Researchers Copyright © 2022 by RMIT University is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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What Is A Literature Review?

A plain-language explainer (with examples).

By:  Derek Jansen (MBA) & Kerryn Warren (PhD) | June 2020 (Updated May 2023)

If you’re faced with writing a dissertation or thesis, chances are you’ve encountered the term “literature review” . If you’re on this page, you’re probably not 100% what the literature review is all about. The good news is that you’ve come to the right place.

Literature Review 101

• What (exactly) is a literature review
• What’s the purpose of the literature review chapter
• How to find high-quality resources
• How to structure your literature review chapter
• Example of an actual literature review

What is a literature review?

The word “literature review” can refer to two related things that are part of the broader literature review process. The first is the task of  reviewing the literature  – i.e. sourcing and reading through the existing research relating to your research topic. The second is the  actual chapter  that you write up in your dissertation, thesis or research project. Let’s look at each of them:

Reviewing the literature

The first step of any literature review is to hunt down and  read through the existing research  that’s relevant to your research topic. To do this, you’ll use a combination of tools (we’ll discuss some of these later) to find journal articles, books, ebooks, research reports, dissertations, theses and any other credible sources of information that relate to your topic. You’ll then  summarise and catalogue these  for easy reference when you write up your literature review chapter. 

The literature review chapter

The second step of the literature review is to write the actual literature review chapter (this is usually the second chapter in a typical dissertation or thesis structure ). At the simplest level, the literature review chapter is an  overview of the key literature  that’s relevant to your research topic. This chapter should provide a smooth-flowing discussion of what research has already been done, what is known, what is unknown and what is contested in relation to your research topic. So, you can think of it as an  integrated review of the state of knowledge  around your research topic. 

What’s the purpose of a literature review?

The literature review chapter has a few important functions within your dissertation, thesis or research project. Let’s take a look at these:

Purpose #1 – Demonstrate your topic knowledge

The first function of the literature review chapter is, quite simply, to show the reader (or marker) that you  know what you’re talking about . In other words, a good literature review chapter demonstrates that you’ve read the relevant existing research and understand what’s going on – who’s said what, what’s agreed upon, disagreed upon and so on. This needs to be  more than just a summary  of who said what – it needs to integrate the existing research to  show how it all fits together  and what’s missing (which leads us to purpose #2, next). 

Purpose #2 – Reveal the research gap that you’ll fill

The second function of the literature review chapter is to  show what’s currently missing  from the existing research, to lay the foundation for your own research topic. In other words, your literature review chapter needs to show that there are currently “missing pieces” in terms of the bigger puzzle, and that  your study will fill one of those research gaps . By doing this, you are showing that your research topic is original and will help contribute to the body of knowledge. In other words, the literature review helps justify your research topic.  

Purpose #3 – Lay the foundation for your conceptual framework

The third function of the literature review is to form the  basis for a conceptual framework . Not every research topic will necessarily have a conceptual framework, but if your topic does require one, it needs to be rooted in your literature review. 

For example, let’s say your research aims to identify the drivers of a certain outcome – the factors which contribute to burnout in office workers. In this case, you’d likely develop a conceptual framework which details the potential factors (e.g. long hours, excessive stress, etc), as well as the outcome (burnout). Those factors would need to emerge from the literature review chapter – they can’t just come from your gut! 

So, in this case, the literature review chapter would uncover each of the potential factors (based on previous studies about burnout), which would then be modelled into a framework. 

Purpose #4 – To inform your methodology

The fourth function of the literature review is to  inform the choice of methodology  for your own research. As we’ve  discussed on the Grad Coach blog , your choice of methodology will be heavily influenced by your research aims, objectives and questions . Given that you’ll be reviewing studies covering a topic close to yours, it makes sense that you could learn a lot from their (well-considered) methodologies.

So, when you’re reviewing the literature, you’ll need to  pay close attention to the research design , methodology and methods used in similar studies, and use these to inform your methodology. Quite often, you’ll be able to  “borrow” from previous studies . This is especially true for quantitative studies , as you can use previously tried and tested measures and scales. 

How do I find articles for my literature review?

Finding quality journal articles is essential to crafting a rock-solid literature review. As you probably already know, not all research is created equally, and so you need to make sure that your literature review is  built on credible research . 

We could write an entire post on how to find quality literature (actually, we have ), but a good starting point is Google Scholar . Google Scholar is essentially the academic equivalent of Google, using Google’s powerful search capabilities to find relevant journal articles and reports. It certainly doesn’t cover every possible resource, but it’s a very useful way to get started on your literature review journey, as it will very quickly give you a good indication of what the  most popular pieces of research  are in your field.

One downside of Google Scholar is that it’s merely a search engine – that is, it lists the articles, but oftentimes  it doesn’t host the articles . So you’ll often hit a paywall when clicking through to journal websites. 

Thankfully, your university should provide you with access to their library, so you can find the article titles using Google Scholar and then search for them by name in your university’s online library. Your university may also provide you with access to  ResearchGate , which is another great source for existing research. 

Remember, the correct search keywords will be super important to get the right information from the start. So, pay close attention to the keywords used in the journal articles you read and use those keywords to search for more articles. If you can’t find a spoon in the kitchen, you haven’t looked in the right drawer. 

Need a helping hand?

How should I structure my literature review?

Unfortunately, there’s no generic universal answer for this one. The structure of your literature review will depend largely on your topic area and your research aims and objectives.

You could potentially structure your literature review chapter according to theme, group, variables , chronologically or per concepts in your field of research. We explain the main approaches to structuring your literature review here . You can also download a copy of our free literature review template to help you establish an initial structure.

In general, it’s also a good idea to start wide (i.e. the big-picture-level) and then narrow down, ending your literature review close to your research questions . However, there’s no universal one “right way” to structure your literature review. The most important thing is not to discuss your sources one after the other like a list – as we touched on earlier, your literature review needs to synthesise the research , not summarise it .

Ultimately, you need to craft your literature review so that it conveys the most important information effectively – it needs to tell a logical story in a digestible way. It’s no use starting off with highly technical terms and then only explaining what these terms mean later. Always assume your reader is not a subject matter expert and hold their hand through a journe y of the literature while keeping the functions of the literature review chapter (which we discussed earlier) front of mind.

Example of a literature review

In the video below, we walk you through a high-quality literature review from a dissertation that earned full distinction. This will give you a clearer view of what a strong literature review looks like in practice and hopefully provide some inspiration for your own. 

Wrapping Up

In this post, we’ve (hopefully) answered the question, “ what is a literature review? “. We’ve also considered the purpose and functions of the literature review, as well as how to find literature and how to structure the literature review chapter. If you’re keen to learn more, check out the literature review section of the Grad Coach blog , as well as our detailed video post covering how to write a literature review . 

Psst… there’s more!

This post is an extract from our bestselling short course, Literature Review Bootcamp . If you want to work smart, you don't want to miss this .

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16 Comments

Thanks for this review. It narrates what’s not been taught as tutors are always in a early to finish their classes.

Thanks for the kind words, Becky. Good luck with your literature review 🙂

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Timothy T. Chol [email protected]

Thank you very much for the guiding in literature review I learn and benefited a lot this make my journey smooth I’ll recommend this site to my friends

This was so useful. Thank you so much.

Hi, Concept was explained nicely by both of you. Thanks a lot for sharing it. It will surely help research scholars to start their Research Journey.

The review is really helpful to me especially during this period of covid-19 pandemic when most universities in my country only offer online classes. Great stuff

Great Brief Explanation, thanks

So helpful to me as a student

GradCoach is a fantastic site with brilliant and modern minds behind it.. I spent weeks decoding the substantial academic Jargon and grounding my initial steps on the research process, which could be shortened to a couple of days through the Gradcoach. Thanks again!

This is an amazing talk. I paved way for myself as a researcher. Thank you GradCoach!

Well-presented overview of the literature!

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How to write a Literature Review: Purpose of a literature review

• Literature review process
• Purpose of a literature review
• Evaluating sources
• Managing sources
• Request a literature search
• Selecting the approach to use
• Quantitative vs qualitative method
• Summary of different research methodologies
• Research design vs research methodology
• Diagram: importance of research
• Attributes of a good research scholar

Books on writing a literature review

Conducting your literature review 

by Susanne Hempel

The purpose of a literature review

Conducting a literature review is a means of demonstrating the  author’s knowledge  about a particular field of study, including vocabulary, theories, key variables and phenomena, and its methods and history. Conducting a literature review also informs the student of the  influential researchers and research groups  in the field (Randolph, 2009).

Literature reviews:

• report on  knowledge and ideas  that have been established on a particular topic, including their  strengths and weaknesses  while they allow you to discover the agreed academic opinion on the topic while at the same time letting you find out the disagreements on the same subject.
• position your research project within the body of literature and thereby  provide perspective  for the reader.
• demonstrate  your knowledge  of the subject area.
• determine what each source contributes to the topic.
• understand the  relationship between the various contributions , identify and (if possible) resolve contradictions, and determine gaps or unanswered questions.
• justify your  choice of research design ; for instance, your choice of qualitative over quantitative approaches, or your method of data analysis.
• clarify how your work fills a  gap  in the scholarly literature.

Writing a literature review also allows you to:

• gain expertise in the ability to scan the literature on a particular topic efficiently, and
• hone your skills in identifying and analysing unbiased and valid data on various topics or fields of study.

Source: Randolph, J.J. 2009.  A guide to writing the dissertation literature review .  Practical Assessment, Research & Evaluation . 14 (13): 1-13.

A literature review is meant to help you to ...

Source: Hart, C. 1998. Doing a literature review: releasing the social science research imagination.  London: Sage, p 27.

S helf No: 300.72 HART

Video clips from the Internet

Click on the  links  below for video clips on how to write literature reviews:

• Honours & Postgraduate Diplomas workshop - Writing the Literature Review - Dr Thuli Shandu Phetla (Unisa)
• Literature Review: step by step guide to writing an effective literature review
• How to write a Literature Review in 30 minutes or less 
• How to Write a Literature Review in 3 Simple Steps
• Literature Review in 5 mins
• Literature Review & Theoretical Framework - Dr KS Malatji

Books on writing a liteature review

Doing a systematic literature review in legal scholarship 

by Marnix Snel and Janaína de Moraes

340.072 SNEL

Doing a literature review in nursing, health and social care 

by  Michael Coughlan & Patricia Cronin

610.73072 COUG

7 steps to a comprehensive literature review : a multimodal & cultural approach

by Anthony J. Onwuegbuzie & Rebecca Frels

001.42 ONWU

Writing the literature review : a practical guide 

by Sara Efrat Efron & Ruth Ravid

808.02 EFRO

• << Previous: Literature review process
• Next: Evaluating sources >>
• Last Updated: Apr 30, 2024 1:19 PM
• URL: https://libguides.unisa.ac.za/literature_review

Literature Review: Purpose of a Literature Review

• Literature Review
• Purpose of a Literature Review
• Work in Progress
• Compiling & Writing
• Books, Articles, & Web Pages
• Types of Literature Reviews
• Departmental Differences
• Citation Styles & Plagiarism
• Know the Difference! Systematic Review vs. Literature Review

The purpose of a literature review is to:

• Provide a foundation of knowledge on a topic
• Identify areas of prior scholarship to prevent duplication and give credit to other researchers
• Identify inconstancies: gaps in research, conflicts in previous studies, open questions left from other research
• Identify the need for additional research (justifying your research)
• Identify the relationship of works in the context of their contribution to the topic and other works
• Place your own research within the context of existing literature, making a case for why further study is needed.

Videos & Tutorials

VIDEO: What is the role of a literature review in research? What's it mean to "review" the literature? Get the big picture of what to expect as part of the process. This video is published under a Creative Commons 3.0 BY-NC-SA US license. License, credits, and contact information can be found here: https://www.lib.ncsu.edu/tutorials/litreview/

Elements in a Literature Review

• Elements in a Literature Review txt of infographic
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The objective of a literature review

Questions to Consider

B. In some fields or contexts, a literature review is referred to as the introduction or the background; why is this true, and does it matter?

The elements of a literature review • The first step in scholarly research is determining the “state of the art” on a topic. This is accomplished by gathering academic research and making sense of it. • The academic literature can be found in scholarly books and journals; the goal is to discover recurring themes, find the latest data, and identify any missing pieces. • The resulting literature review organizes the research in such a way that tells a story about the topic or issue.

The literature review tells a story in which one well-paraphrased summary from a relevant source contributes to and connects with the next in a logical manner, developing and fulfilling the message of the author. It includes analysis of the arguments from the literature, as well as revealing consistent and inconsistent findings. How do varying author insights differ from or conform to previous arguments?

Language in Action

A. How are the terms “critique” and “review” used in everyday life? How are they used in an academic context?

In terms of content, a literature review is intended to:

• Set up a theoretical framework for further research • Show a clear understanding of the key concepts/studies/models related to the topic • Demonstrate knowledge about the history of the research area and any related controversies • Clarify significant definitions and terminology • Develop a space in the existing work for new research

The literature consists of the published works that document a scholarly conversation or progression on a problem or topic in a field of study. Among these are documents that explain the background and show the loose ends in the established research on which a proposed project is based. Although a literature review focuses on primary, peer -reviewed resources, it may begin with background subject information generally found in secondary and tertiary sources such as books and encyclopedias. Following that essential overview, the seminal literature of the field is explored. As a result, while a literature review may consist of research articles tightly focused on a topic with secondary and tertiary sources used more sparingly, all three types of information (primary, secondary, tertiary) are critical.

The literature review, often referred to as the Background or Introduction to a research paper that presents methods, materials, results and discussion, exists in every field and serves many functions in research writing.

Adapted from Frederiksen, L., & Phelps, S. F. (2017). Literature Reviews for Education and Nursing Graduate Students. Open Textbook Library

Review and Reinforce

Two common approaches are simply outlined here. Which seems more common? Which more productive? Why? A. Forward exploration 1. Sources on a topic or problem are gathered. 2. Salient themes are discovered. 3. Research gaps are considered for future research. B. Backward exploration 1. Sources pertaining to an existing research project are gathered. 2. The justification of the research project’s methods or materials are explained and supported based on previously documented research.

Media Attributions

• 2589960988_3eeca91ba4_o © Untitled blue is licensed under a CC BY (Attribution) license

Sourcing, summarizing, and synthesizing:  Skills for effective research writing  Copyright © 2023 by Wendy L. McBride is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Literature Review: A Definition

What is a literature review, then.

A literature review discusses and analyses published information in a particular subject area.   Sometimes the information covers a certain time period.

A literature review is more than a summary of the sources, it has an organizational pattern that combines both summary and synthesis. A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information. It might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. And depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.

But how is a literature review different from an academic research paper?

While the main focus of an academic research paper is to support your own argument, the focus of a literature review is to summarize and synthesize the arguments and ideas of others. The academic research paper also covers a range of sources, but it is usually a select number of sources, because the emphasis is on the argument. Likewise, a literature review can also have an "argument," but it is not as important as covering a number of sources. In short, an academic research paper and a literature review contain some of the same elements. In fact, many academic research papers will contain a literature review section. What aspect of the study (either the argument or the sources) that is emphasized determines what type of document it is.

( "Literature Reviews" from The Writing Center, University of North Carolina at Chapel Hill )

Why do we write literature reviews?

Literature reviews provide you with a handy guide to a particular topic. If you have limited time to conduct research, literature reviews can give you an overview or act as a stepping stone.

For professionals, they are useful reports that keep them up to date with what is current in the field.

For scholars, the depth and breadth of the literature review emphasizes the credibility of the writer in his or her field. Literature reviews also provide a solid background for a research paper's investigation.

Comprehensive knowledge of the literature of the field is essential to most research papers.

Journal Articles on Writing Literature Reviews

• Research Methods for Comprehensive Science Literature Reviews Author: Brown,Barry N. Journal: Issues in Science & Technology Librarianship Date: Spring2009 Issue: 57 Page: 1 more... less... Finding some information on most topics is easy. There are abundant sources of information readily available. However, completing a comprehensive literature review on a particular topic is often difficult, laborious, and time intensive; the project requires organization, persistence, and an understanding of the scholarly communication and publishing process. This paper briefly outlines methods of conducting a comprehensive literature review for science topics. [ABSTRACT FROM AUTHOR];
• Research: Considerations in Writing a Literature Review Authors: Black,K. Journal: The New Social Worker Date: 01/01; 2007 Volume: 14 Issue: 2 Page: 12 more... less... Literature reviews are ubiquitous in academic journals, scholarly reports, and social work education. Conducting and writing a good literature review is both personally and professionally satisfying. (Journal abstract).
• How to do (or not to do) A Critical Literature Review Authors: Jesson,Jill; Lacey,Fiona Journal: Pharmacy Education Pub Date: 2006 Volume: 6 Issue: 2 Pages:139 - 148 more... less... More and more students are required to perform a critical literature review as part of their undergraduate or postgraduate studies. Whilst most of the latest research methods textbooks advise how to do a literature search, very few cover the literature review. This paper covers two types of review: a critical literature review and a systematic review. [ABSTRACT FROM AUTHOR]
• Conducting a Literature Review Authors: Rowley,Jennifer; Slack,Frances Journal: Management Research News Pub Date: 2004 Volume: 27 Issue: 6 Pages:31-39 more... less... Abstract: This article offers support and guidance for students undertaking a literature review as part of their dissertation during an undergraduate or Masters course. A literature review is a summary of a subject field that supports the identification of specific research questions. A literature review needs to draw on and evaluate a range of different types of sources including academic and professional journal articles, books, and web-based resources. The literature search helps in the identification and location of relevant documents and other sources. Search engines can be used to search web resources and bibliographic databases. Conceptual frameworks can be a useful tool in developing an understanding of a subject area. Creating the literature review involves the stages of: scanning, making notes, structuring the literature review, writing the literature review, and building a bibliography.

Some Books from the WU Catalog

• The SAGE handbook of visual research methods [electronic resource] by Edited by Luc Pauwels and Dawn Mannay. ISBN: 9781526417015 Publication Date: SAGE Publications, Inc., 2020.

Helpful Websites

• "How to do a Literature Review" from Ferdinand D. Bluford Library
• "The Literature Review: A Few Tips on Conducting It." from the University of Toronto
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• Last Updated: May 30, 2024 10:41 AM
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What is Literature Review? Importance, Functions, Process,

• Post last modified: 13 August 2023
• Reading time: 12 mins read
• Post category: Research Methodology

What is Literature Review?

A literature review is a critical and comprehensive analysis of existing research, studies, articles, books, and other relevant sources on a specific topic or subject. It serves as a foundational step in the research process, helping researchers understand the current state of knowledge, identify gaps in the literature, and establish a context for their own study.

Table of Content

• 1 What is Literature Review?
• 2 Importance of a Literature Review
• 3 Functions of a Literature Review
• 4.1 Search the Existing Literature in Your Field of Interest
• 4.2 Review the Literature Obtained
• 4.3 Develop a Theoretical Framework
• 4.4 Write the Literature Review
• 5 How to Write a Literature Review
• 6 Types of Sources for Review

In most research reports or research papers, you will see that literature review is an essential element and it forms the basis for advancing knowledge, facilitates theory development, discovers new research areas and closes old ones. When researchers want to understand the management dilemma, they study various books, articles and all other available sources.

In the research reports, the researchers present a summary of their search, study and evaluation of the literature that is already available related to the research topic. When the researcher presents a summary of their study of present literature in addition to their analysis of how this literature is related to or essential for the current research report; then, this process is known as literature review.

For example, in a research paper titled ‘Attrition Analysis in a Leading Sales Organisation in India’, authored by Mamta Mohapatra (International Management Institute, New Delhi, India), Amisha Gupta (Birlasoft, New Delhi, India) and Nikita Lamba (Genpact, New Delhi, India), literature review is presented as follows:

Organisations and researchers usually conduct literature review in order to establish how their own research fits within the context of existing literature.

Apart from these, some other objectives of carrying out literature review are:

• Develop an understanding of how each source of literature helps in understanding the research problem
• Examine the interrelationships among different variables
• Find out ways to interpret earlier similar researches on the topic under study
• Rectify the conflicts that exist among previously conducted studies
• Get an idea regarding the required sample size
• Get an estimate of how much variance is there in the variables of interest
• Understand the type of relationship that exists among variables
• Determine the research method that can be used in the research

Importance of a Literature Review

There are various reasons for carrying out literature review. Majorly, literature review helps in:

• Assessing the current state and level of research on a given topic
• Identifying experts related to particular research
• Identifying questions that need further research and exploration
• Identifying what methodologies have been used in the related past studies and what methodology should be used in current research
• Justifying a proposed research methodology
• Indicating the originality and relevance of the given research problem
• Demonstrating the preparedness of a researcher to complete the research

Functions of a Literature Review

Some of the major functions of literature review are:

• Establishing a context for the research
• Demonstrating that the researcher has actually read related literature extensively and is aware of most theory and methodology related to the given research topic
• Providing a shape for the research under consideration
• Establishing a connection between what the researcher is proposing and what he has already read
• Demonstrating how the findings of researcher can be integrated with the already existing research findings.
• Revealing the differences or areas of gap between present and earlier research findings
• Improving researcher’s research methodology
• Expanding researcher’s knowledge base
• Ensuring that the researcher is carrying out new research that has not been carried out earlier

Process of a Literature Review

The second step in the research process is to carry out the review of already existing literature. Before engaging in literature review, the researcher must be clear as to what is the area and topic of research. There are four steps involved in the literature review process as shown in Figure:

Search the Existing Literature in Your Field of Interest

In the literature review process, the first step is to find out what research has already been done in the area that the researcher has chosen. This step involves preparing a list or bibliography of existing sources of relevant literature such as books, journals, abstracts of articles on your research topic, citation indices and digital libraries.

Review the Literature Obtained

After the researcher has identified related literature including journals, books, research papers, etc.; the next step is to study, evaluate and analyse the literature critically. This study of literature helps a researcher identify themes and issues related to the research topic.

An evaluation of literature helps in:

• Identifying the different theories and their criticism
• Identifying different methodologies used in different studies including their sample size, data used, measurement methods
• Assessing if the researcher’s theory is confirmed beyond doubt
• Preparing a list of different opinions of different researchers and researcher should also add his/her opinion about the validity of these different opinions

Develop a Theoretical Framework

Since carrying out literature review is a time-consuming activity but the researcher has to do it within a limited time. In order to do so, the researcher usually establishes a boundary and parameters for the research work. Also, the researcher must sort information obtained from all the sources of literature. For a researcher, the theoretical framework acts as a base on which he can further or extend his research. At times, the researchers may modify their research framework after analysing the available literature.

Write the Literature Review

The last step in literature review is to make a summary of all the literature that the researcher has studied and reviewed. Usually, writing a literature review starts with a write-up on the main theme of research followed by the important ideas on which the research would focus. After this, the all the major themes and sub-themes to be discussed are organised and related. This will help the researcher in structuring the literature review. The researcher should also identify and describe the theories and studies that are relevant for the study under consideration. The researcher should then list and describe all the gaps that are present in the current body of knowledge. In addition, the researcher may also explain the recent advances and trends in the given research field. To conclude, the researcher should compare and evaluate his findings on the basis of research assumptions, related research theories, hypotheses, applied research designs, variables selected and potential future work speculated by the researchers. Finally, the researcher must acknowledge, cite and quote all the sources that he/she has used in his research. One specific characteristic of literature review is that the researcher must ensure that he gives due credit to all people who have contributed in the research work.

How to Write a Literature Review

While writing the literature review, the researcher must adopt or adhere to certain strategies as follows:

• Establish a focus around the central theme and ideas of the research
• Describe what a reader can expect from the given research study
• Organise the literature research to include basic elements such as introduction, body and conclusions

Types of Sources for Review

A researcher usually uses secondary data for literature review. Some of the major and widely used sources for literature reviews include articles in professional journals, statistical data from government websites and website material from professional organisations.

Apart from the previously mentioned sources, certain other sources of data can also be used by researchers that provide them first-hand information that is important for the study. These sources include reports, theses, emails, letters, conference proceedings, company reports, autobiographies, official reports, research articles, etc.

Apart from these, the researcher may also refer to other such as review articles, academic journals, books, newspapers, documentaries, encyclopaedias, dictionaries, bibliographies and citation indexes.

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Survey of the loss function in classification models: Comparative study in healthcare and medicine

• Published: 05 June 2024

Cite this article

• Sepideh Etemadi 1 &
• Mehdi Khashei 1 , 2  

The selection of an appropriate classification approach depends heavily on the classification rate, which is the most important factor in achieving the desired decision quality. While researchers have examined the impact of different features on the performance of classification approaches, cost/loss functions have received less attention in the comparative literature review, despite their theoretical significance in influencing the classification rate. This paper aims to address this gap by conducting a comparative study on the influence of different cost/loss functions on the classification rate of diverse classifiers. To achieve this objective, the study considers the five most popular and commonly utilized types of cost/loss functions: linear and nonlinear continuous, linear and nonlinear semi-continuous, and discrete cost/loss functions. Furthermore, it takes into consideration the three primary categories of classification approaches: statistical, intelligent, and deep learning classifiers. In addition, a total of 44 benchmark datasets from three distinct domains of medicine, specifically cancer and disease diagnosis, therapy, and biology science, are chosen for analysis. Based on empirical findings, it is evident that the selection of cost/loss functions has a notable impact on the classification rate. The numerical results demonstrate that the discrete cost/loss function performs the best, followed by the semi-continuous and continuous cost/loss functions, in that order. This clearly highlights the positive and direct correlation between aligning the cost/loss function with the goal function of classification approaches and achieving a higher classification rate. Moreover, the average effectiveness of the nonlinear versions of the semi-continuous and continuous cost/loss functions is comparable to that of their linear counterparts. While the choice of cost/loss function can influence the classification rate of various classifiers, the degree of improvement varies depending on the classifier type. In general, statistical classifiers demonstrate a greater degree of enhancement, followed by intelligent classifiers and deep learning models in second and third positions, respectively. Overall, the study reveals a negative correlation between the complexity of classifiers and the improvement in the classification rate when altering the cost/loss function. Furthermore, the numerical findings suggest that the variations in the degree of improvement achieved by changing the cost/loss functions are substantial and affected by the type and domain of the data.

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Etemadi S, Khashei M (2022) Accuracy versus reliability-based modelling approaches for medical decision making. Comput Biol Med 141:105138. https://doi.org/10.1016/j.compbiomed.2021.105138

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Etemadi, S., Khashei, M. Survey of the loss function in classification models: Comparative study in healthcare and medicine. Multimed Tools Appl (2024). https://doi.org/10.1007/s11042-024-19543-8

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Exploring the Relationship between Micronutrients and Athletic Performance: A Comprehensive Scientific Systematic Review of the Literature in Sports Medicine

Hadeel ali ghazzawi.

1 Department Nutrition and Food Technology, School of Agriculture, The University of Jordan, Amman 11942, Jordan; moc.kooltuo@89tadaraj_ranam (M.J.); moc.liamg@idiabolasodnos (S.A.);

Mariam Ali Hussain

2 Department of Psychiatry, College of Medicine and Medical Sciences, Arabian Gulf University, Manama 323, Bahrain; hb.ude.uga@hhamairam (M.A.H.); hb.ude.uga@zmajidahk (K.M.R.); moc.liamg@849ydneslaalwahk (K.K.A.);

Khadija Majdy Raziq

Khawla khaled alsendi, reem osama alaamer, manar jaradat, sondos alobaidi, raghad al aqili, khaled trabelsi.

3 High Institute of Sport and Physical Education of Sfax, University of Sfax, Sfax 3000, Tunisia

4 Research Laboratory—Education, Motricity, Sport and Health, University of Sfax, Sfax 3000, Tunisia

Haitham Jahrami

5 Government Hospitals, Ministry of Health, Manama 323, Bahrain

Associated Data

All data are available in the manuscript.

The aim of this systematic review is twofold: (i) to examine the effects of micronutrient intake on athletic performance and (ii) to determine the specific micronutrients, such as vitamins, minerals, and antioxidants, that offer the most significant enhancements in terms of athletic performance, with the goal of providing guidance to athletes and coaches in optimizing their nutritional strategies. The study conducted a systematic search of electronic databases (i.e., PubMed, Web of Science, Scopus) using keywords pertaining to micronutrients, athletic performance, and exercise. The search involved particular criteria of studies published in English between 1950 and 2023. The findings suggest that vitamins and minerals are crucial for an athlete’s health and physical performance, and no single micronutrient is more important than others. Micronutrients are necessary for optimal metabolic body’s functions such as energy production, muscle growth, and recovery, which are all important for sport performance. Meeting the daily intake requirement of micronutrients is essential for athletes, and while a balanced diet that includes healthy lean protein sources, whole grains, fruits, and vegetables is generally sufficient, athletes who are unable to meet their micronutrient needs due to malabsorption or specific deficiencies may benefit from taking multivitamin supplements. However, athletes should only take micronutrient supplements with the consultation of a specialized physician or nutritionist and avoid taking them without confirming a deficiency.

1. Introduction

Optimal performance is a primary objective for many athletes, and this can be attained by following a suitable exercise protocol and ensuring proper nutrition [ 1 ]. Food is composed of nutrients that are essential for growth, repair, and energy generation depending on the amount that meets the body’s need [ 2 ]. Nutrients are typically categorized into two main groups: micronutrients and macronutrients [ 3 ]. When it comes to athletic performance, the importance of micronutrients should not be neglected [ 4 ]. Athletes are prone to consuming insufficient amounts of micronutrients due to inappropriate dietary habits, especially if they are not matching their physical activity requirements [ 5 ]. By making sure they are receiving adequate levels of micronutrients, athletes can give themselves a competitive edge and maximize the potential of their training [ 6 ]. Micronutrients may boost mental performance, help balance hormones, and keep cognitive performance at its peak [ 7 ].

It is noteworthy to emphasize that sports nutrition is not a one-size-fits-all solution, as each athlete has specific nutritional needs [ 7 ]. Therefore, athletes, nutritionists, and coaches must work together to customize nutritional plans for each athlete to ensure that their athletes/players’ needs are considered properly and they are receiving the sufficient level of nutrients they need to aid in the adaptation to their training and ultimately support optimal athletic performance. The evaluation of the evidence of the impact of micronutrients on the performance of athletes is the main purpose of this comprehensive systematic review paper.

2. Methods and Search Strategy

A comprehensive literature search was conducted using the Web of Science, Scopus, and PubMed databases. In order to retrieve relevant studies on the topic, our search strategy incorporated keywords including “micronutrients”, “vitamins”, “minerals”,” antioxidants”, “athletes”, “sport performance”, “training”, and “exercise”. Original research articles involving human subjects, English-language publications, human subjects, and a focus on micronutrients and athletic performance were the inclusion criteria. For the systematic review procedure, the Synthesis without meta-analysis (SWIM) recommendations were followed. The search was limited to articles published between January 1950 and 31 March 2023. The studies that made the cut for the review had to measure outcomes related to athletic performance, have a sample size of at least 10 participants, and use an intervention involving a micronutrient supplement. Studies that concentrated on macronutrients—such as carbohydrates and protein—were disregarded.

2.1. Data Extraction

Studies’ titles and abstracts located by the search were examined by two independent reviewers. After that, full-text articles were examined to see if they qualified for inclusion in the review. Data on the study design, sample size, intervention protocol, micronutrient supplements used, athletic performance outcomes assessed, and outcomes were extracted from the eligible studies.

2.2. Data Synthesis

To summarize the conclusions of the included studies, a narrative synthesis was carried out. The studies’ findings were categorized by micronutrient supplement and athletic performance outcome measures. A description of each study’s design, sample size, intervention strategy, and findings was included in the synthesis. It is important to ensure the accuracy and reliability of a systematic review by ensuring that all information is extracted in a standardized and consistent manner. In this study, two authors independently extracted all information from each paper to minimize the risk of bias and errors. This approach helps to ensure the validity of the review’s findings and strengthens the overall quality of the study. By having two authors independently extract information from each paper, the review can ensure data accuracy and increase confidence in the conclusions drawn from the analysis. It is a rigorous method that is commonly used in systematic reviews and emphasizes the importance of transparency and objectivity in research [ 8 ].

A total of 231 articles were obtained involving 18,683 athletes. Table 1 provides a summary of the main micronutrients researched in sports medicine. Table 2 provides a summary of all available 217 research articles about micronutrients and sports performance. Figure 1 simplified the model of micronutrients’ main functions in sports medicine.

Model of micronutrients’ main functions in sports medicine.

Dietary Difference Intake and Top Sources of Vitamins and Minerals.

Abbreviations: µg: microgram; DNA: deoxyribonucleic acid; IU: international unit; mg: milligram; ROS: reactive oxygen species.

Comprehensive overview of articles about micronutrients and sport performance.

4. Vitamins

Vitamins are organic essential compounds that cannot be synthesized by the human body [ 29 ]. They play a vital role in numerous functions that are relevant to the athlete’s performance [ 7 ]. Their functions are evident in co-enzymes, hormones, and autoxidation, as well as their contribution to energy production [ 242 ]. There are thirteen various kinds of vitamins currently divided into two major groups due to their chemical and biological functions, four of which are fat-soluble vitamins (FSV) including vitamins A, D, E, and K, and the rest are water-soluble vitamins (WSV) including B complex vitamins and vitamin C [ 243 ]. Table 1 summarizes the recommendation requirements of vitamins along with the rich sources and their roles in exercise performance.

5. Fat-Soluble Vitamins (FSV)

Vitamin A plays a significant role in promoting the overall wellbeing of athletes, as it aids in the formation of healthy tissues and improves oxygen access throughout the body, thereby supporting the maintenance of an adequate level of physical activity [ 3 ]. It also has a crucial influence on vision, skin health, and immune system functioning [ 29 ]. Moreover, vitamin A is a potent antioxidant that helps in neutralizing free radicals generated by oxidative stress during advanced physical training. The sufficient consumption of vitamin A may help alleviate the reactive oxygen species and avoid the onset of illnesses such as heart failure and muscle damage [ 244 ], as mentioned in many studies in Table 2 .

Vitamin A mainly exists in two forms: animal source (retinol) and plant-based provitamin A (carotenoids). The intake of sufficient amounts of beef liver, eggs, dairy products, and seafood as well as dark leafy green vegetables may ensure meeting the dietary requirements for athletes. It is noteworthy that athletes may benefit from supplementation with multivitamins that contain vitamin A, as a part rather than its own sole use [ 29 ].

Vitamin A has been proved to enhance and support various body functions, including reaction time, muscles recovery [ 245 , 246 ], and protein synthesis, which is essential for muscle growth and recovery and can be important for those competing in events requiring fast reflexes [ 247 ]. Furthermore, vitamin A can help protect athletes against injuries by increasing healing times and promoting the formation of healthy connective tissues [ 3 ]. Finally, vitamin A may help fight off colds, flu, and other illnesses, which can be particularly helpful for traveling athletes.

To evaluate the effect of crocetin on fatigue, a study test was conducted by athletes to measure stamina using a bicycle ergometer at a standard workload for 120 min twice. They also performed non-workload tests of 10 s at 30 min at a maximum velocity (MV) [ 242 ]. A difference in MV from 30 to the 210 min test was remarkably reported only in men who consumed crocetin when compared to their counterpart who used a placebo ( p < 0.05) [ 248 ]. No difference was observed with the consumption of ascorbic acid in all candidates with the same period [ 248 ]. The daily consumption of crocetin would reduce physical exhaustion in men, according to these results [ 179 ]. The attenuating effect of saffron carotenoids on muscle fatigue is due to their provitamin A activity [ 248 ]. Athletes should meet their daily recommended intake of vitamin A to guarantee a perfect peak physical condition [ 249 ].

The Recommended Dietary Allowance (RDA) of retinol activity equivalents (mcg RAE), as shown in Table 1 , is 900 micrograms for men aged 19 years old and older, equal to 3000 international units (IU), and 700 mcg RAE for women aged 19 years old and older, equivalent to 2333 (IU). However, the adherence to a maximum Tolerable Upper Limit (UL) of 10,000 IU (3000 mcg)/day for adults is important to avoid any dangerous effect. It is also important to emphasize that toxicity may occur when frequent doses of more than 25,000 IU are taken daily [ 3 ].

β-carotene is a member of the carotenoid family that is thought to provide numerous health benefits, including immunity system boosting, antioxidation properties, and performance enhancement [ 250 ]. β-carotene is an essential antioxidant, meaning that it helps prevent the harmful effect of free radicals on cells [ 251 ]. This is important for athletes, as free radicals are generated during strenuous exercise and can lead to fatigue and soreness [ 176 ]. Several studies have reported similar findings, highlighting the ability of vitamin A to potentially reduce recovery time from exercise [ 7 , 250 ]

Sumac juice drink was tested in a study to evaluate its impact on pain scores through post-exercise intervals. Forty healthy candidates involved in an aerobic training protocol for four weeks received a dose of placebo or sumac juice consumption two times/day for a month. The results revealed that participants of the sumac juice group had a lower pain score increment and even a better enhancement during pain relief. The potency of protecting muscles might be due to the sumac juice antioxidant potency of β-carotene-linoleic acid components. These results highlight the possibility of sumac juice consumption in improving muscle performance among athletes [ 252 ]. Nevertheless, future studies of athletes are warranted.

Athletes often push their bodies to the limit, therefore compromising their immune systems and making them more susceptible to infections and illness [ 176 ]. Taking a supplement with β-carotene may have potential benefits for the immune system, helping to prevent illness and potentially enabling athletes to train harder and longer [ 250 , 251 ]. Apparently healthy nonsmoker adult males were involved in consuming placebo or 15 mg/day of β-carotene for 26 days. After oral administration, significant increases in the monocytes percentage representing the major histocompatibility complex class II molecule human leukocyte antigen DR isotype (HLA-DR) and the adhesion molecules intercellular adhesion molecule-1 and leukocyte function-associated antigen-3 were observed. Furthermore, tumor necrosis factor-alpha (TNF-alpha) was notably elevated due to the dose intake, arguing that a slight increment in the consumption of dietary β-carotene can enhance the responses of immune cells within the short term, supporting the process of the carcinogenic potency [ 253 ].

Lastly, β-carotene has been found to improve physical performance [ 254 ]. Studies have shown that β-carotene supplementation may lead to endurance strength improvement and injury risk prevention [ 3 , 150 ]. Similarly, a meta-analysis of nine studies including participants from both genders, with a total 190,545 candidates, emphasized that β-carotene leads to a significant enhancement in overall performance [ 29 ]. There was a 95% possibility that β-carotene consumption attenuates the possibility of hip fracture and other different fracture types by over 20% [ 251 ]. According to research, despite the uncertain effect of the antioxidant’s supplementation, consuming β-carotene and combining antioxidants or not still has an effective impact in reducing exercise-induced peroxidation [ 33 ]. This may enhance athletes’ endurance in the long term [ 251 , 254 , 255 ].

6. Vitamin E

As research progresses, the potential advantages of vitamin E for athletes are becoming increasingly apparent. Vitamin E helps in protecting athletes’ bodies and may improve both performance and recovery [ 75 ]. Overtraining and intense exercise are associated with reactive oxygen species (ROSs) production, which aids in enhanced muscular and endurance adaptation to exercise through the upregulation of endogenous antioxidant enzymes [ 256 ]. However, excess accumulation of ROS accompanied by the inability of the body to scavenge these compounds is harmful to the body’s cell components which is associated with fatigue, delayed recovery, and reduced performance [ 257 ]. Accordingly, research suggests the possible protective effects of vitamin E supplements against chronic stress associated with exercise [ 257 , 258 ]. This vitamin possesses antioxidant properties by neutralizing free radicals, protecting cells and tissues [ 257 , 258 ].

Studies showed controversial results of vitamin E supplementation in athletes [ 44 ]. It was shown that vitamin E supplements neither inhibit exercise-induced oxidative stress nor impact endurance running performance [ 259 ]. Moreover, these results were supported by the randomized controlled trial on athletic students where vitamin E oral consumption was found to not influence exercise endurance [ 260 ]. On the other hand, among healthy individuals, vitamin E (alpha-tocopherol) consumption inhibits the exercise-induced reduction in blood paraoxonase 1/arylesterase activity [ 6 , 44 , 147 , 260 ]. Excess doses of supplements have been shown in studies to inhibit the signaling reactions required for adaptations to exercise, creating an interference effect [ 3 ].

A meta-analysis revealed that vitamin E supplements have a beneficial and protective effect, particularly at low doses (≤500 IU/day), in reducing biomarkers associated with exercise-induced muscle damage and oxidative stress. Beneficial effects of the antioxidant characteristics of vitamin E were observed among exercise-induced side-effects [ 257 ]; both animal and human studies have indicated that Vitamin E has the potential to enhance immune function and provide protection against various infectious diseases [ 6 ]. Vitamin E reduces PGE2 production and inhibits COX2 activity, likely by decreasing nitric oxide production [ 261 ]. Furthermore, it improves T cells immune synapse formation and activation signals, and lastly, it helps in modulating the T (Th1/Th2) balance [ 52 ]. This is particularly beneficial for athletes, who are often susceptible to illness and injury due to the intense physical demands of their sport. By supplementing with vitamin E, athletes can help increase the body’s natural immunity, thus reducing the risk of infection and promoting recovery [ 262 ].

Vitamin E may assist in improving blood flow, which is essential for athletes [ 242 ]. γ-tocopherol, which is one of the compounds that contain vitamin E, increases cardiovascular functions. γ-tocopherol expands the activity of nitric oxide synthase, which in turn produces nitric oxide, aiding in vessels relaxation and thus improving blood flow [ 29 ]. Adequate levels of nutrients and oxygen concentrations in muscles indicate a raised blood flow rate, which may help improve performance [ 263 ]. Additionally, vitamin E improves red blood cells’ flow and flexibility [ 264 ]. This is important for athletes, as improved blood flow means better performance in delivering nutrients and oxygen to the muscles, allowing them to perform at their best [ 176 ].

Free radicals such as superoxide, nitric oxide, and hydrogen peroxide are known to be of significant importance, as there must be a balance between antioxidants and free radicals in order to obtain physiological muscle adaptation in response to exercise [ 25 ]. Few studies suggested that antioxidants supplementation may be beneficial under specific circumstances, such as overtraining, high-altitude training, or hypoxic training, and claimed that antioxidant usage such as the intake of vitamin E or vitamin C may have no benefit at all or may even cause harm [ 6 , 7 , 29 , 176 , 256 ]. Misusing or consuming excessive amounts of vitamins can lead to muscle fatigue and impede the recovery process due to the inactivation of the gene expression regulator Nrf2 (Nuclear factor erythroid 2-related factor 2), which plays a role in the response to cellular stress and contributes to enhancing exercise performance [ 265 ]. It is worth noting that Vitamin E toxicity may cause increases in mortality risk factors, since there has been a positive relation accompanied by a high-sensitivity C reactive protein indicative of inflammation [ 266 ].

7. Vitamin D

Vitamin D plays a cooperative role in the synthesis of various hormones in the body [ 3 ]. Dairy products, egg yolk, and fatty fish are the rich dietary intake sources [ 2 ]. Moreover, it can be synthesized in vivo and be activated by sunlight within a duration of 15 to 20 min of exposure [ 44 ]. It also plays an important role in calcium homeostasis and constant healthy bone [ 30 ], functions of improving the immune system, musculoskeletal system, power, and force output [ 45 ].

Vitamin D supplementation has been increased among athletes [ 45 ]. Unfortunately, the widespread vitamin D insufficiency has been clearly stated in elite male athletes, with evidence of a deficit in women [ 46 ]. Percentages of insufficiency in elite athletes were above 50%, and the deficiency in other studies was 70–90%, as reported by Harju et al. [ 47 ]. Certain circumstances impact vitamin D status, such as indoor training, pigmented skin, and living in a high-altitude region [ 48 ]. Studies have reported that athletes with vitamin D deficiency may experience ergogenic benefits when taking vitamin D supplements [ 103 ].

There was a direct relation between the concentrations of vitamin D and athletes’ performance, such as speed, jumps’ height, power muscle tone, and strength of handgrip [ 50 ]. Moreover, the addition of calcium to vitamin D supplements exhibited a reduction in the stress fracture rate [ 106 , 138 ].

In a study conducted among 70 athletes randomly assigned for 8 weeks to either vitamin D oral supplements of 50,000 IU/week group or a control group, a significant improvement in the test of the strength leg press in both groups was reported [ 267 ]. However, the results emphasized that the enhancement in the supplemented group was obviously more noted than that in the control group ( p = 0.034). Moreover, when the sprint test was conducted, within-group enhancement had been noticed in the supplemented group only ( p = 0.030). The results showed that regular weekly vitamin D supplementation with a dose of 50,000 IU increased the levels of circulating calcidiol (major circulating form of vitamin D) by approximately 17 ng/mL. This increment was related to a notable enhancement in sprint and power leg examinations in the vitamin D group [ 138 ]

Additionally, vitamin D is also thought to improve the body’s utilization of carbohydrates during exercise, providing the body with increased energy, which can help to enhance performance [ 1 ]. Twenty-two male adult athletes were allocated into two groups for 8 days: a one-shot dose of 150,000 IU vitamin D group and a placebo group. The vitamin D group showed a significant elevation in muscle power in the period from day 1 up to day 8, suggesting that a single dose of 150 000 IU vitamin D had a beneficial impact on serum 25-hydroxy vitamin D (25(OH)D) levels and the muscle’s role [ 268 ].

To maintain sufficient vitamin D levels, the most appropriate way is to spend time in outdoor direct sunlight for several minutes each day, as obviously indicated by many studies’ conclusions (see Table 2 ). This prescription for sun exposure should also be combined with foods that are rich in vitamin D, such as dairy products, fatty fish, and fortified foods [ 101 ]. Additionally, athletes may also benefit from daily multivitamin supplements that contain vitamin D to ensure that their body receives the best possible nutrition. The recommended daily dose of vitamin D, as shown in Table 1 , varies depending on age; a daily dose of 600 IU (equivalent to 15 micrograms (mcg)) is considered sufficient for the age of 19 and above in both genders, and for adults over 70 years old, an 800 IU (20 mcg) daily dose would be sufficient [ 7 , 25 ]. Vitamin D-deficient athletes would require 50,000 IU of vitamin D per week for 8 weeks [ 138 , 258 ].

A previous study was conducted for 12 weeks among 53 youth athlete swimmers who suffered from insufficient levels of vitamin D to evaluate the influence of vitamin D oral supplementation on physical performance by taking 2000 IU/day of vitamin D or placebo. No notable difference was observed in performance between the supplemented and placebo groups [ 269 ]. The results concluded that there was no remarkable correlation found between Vitamin D levels and the evaluated criteria including strength or swimming performance and even the age-adjusted balance. Although the oral administration of vitamin D had raised the concentration of Vitamin D compared to the placebo group, no significant physical performance enhancement was reported [ 269 ].

8. Vitamin K

Vitamin K is essential for blood coagulation [ 163 ]. It may also impact bone metabolism in postmenopausal women, according to a few previous studies [ 3 , 7 , 270 ]. In elite female athletes, the oral intake of vitamin K at a dose of 10 mg/day has been shown to improve bone remodeling [ 254 ] by increasing the calcium-binding capacity of osteocalcin, promoting bone formation, and reducing bone resorption [ 176 ]. Moreover, the intake of vitamin K improved cardiovascular function [ 18 , 231 ]. Table 1 summarized the recommendation and the role of vitamin K in exercise performance.

9. Water-Soluble Vitamins (WSV)

B-complex vitamins are essential for athletes to maintain optimal health and performance [ 19 ]. B-complex vitamins help athletes manage stress and anxiety, aid in muscle recovery, and reduce fatigue, which may adversely affect performance if left unchecked [ 2 ]. B-complex vitamins help in blood pressure regulation [ 271 ]. Moreover, B-complex vitamins aid in maintaining a healthy sleep schedule by regulating levels of the sleep-regulating hormone melatonin, helping athletes fall in a deep continuous sleep [ 5 ]. This is essential for athletes, as the lack of sleep can affect an athlete’s performance [ 52 ]. B-complex vitamins also contribute to maintaining optimal health and performance in athletes, supporting improved brain functioning, concentration, sleep quality, and energy levels [ 19 ]. Thus, athletes need to ensure that they are receiving enough vitamin B through their diet or supplements [ 244 ].

Thiamine (B1) is a water-soluble vitamin that must be consumed regularly from the diet [ 6 ]. Although free thiamine is stable at acidic pH, it is destroyed by ultraviolet (UV) and gamma irradiation and is heat-sensitive [ 29 ]. Whole grains, bread, and nuts are the most common thiamine food sources, while milled wheat flour, polished rice, vegetables, and fruits contain less thiamin [ 272 ]. The large intestine’s bacteria in the human body are able to produce thiamine and thiamine pyrophosphate (TPP) [ 52 ]. Thiamine leaches into the water due to its solubility and is inevitably lost in any discarded soaking or cooking water, as well as destroyed by heating during culinary methods [ 7 ].

Thiamine, in its active state (TPP), is a cofactor of numerous important enzymes involved in the metabolism of carbohydrates and branched-chain amino acids [ 7 ]. Moreover, it is necessary for several other cellular functions, including the development of nucleic acid precursors, myelin, and neurotransmitters (such as acetylcholine), as well as antioxidant defense [ 272 ]. A deficiency of this vitamin leads to a decline in oxidative metabolism [ 265 ]. The biochemical outcomes include a failure to create adenosine triphosphate (ATP), lactic acidosis resulting in a greater lactic acid generation, and a reduction in neurotransmitter synthesis (e.g., acetylcholine, glutamate, aspartate, and gamma-aminobutyric acid (GABA)) [ 6 ]. The major causes of thiamin deficiency are either the insufficient intake, poor absorption or metabolism, or an increase the body demand [ 265 ]. Furthermore, diuretics and diarrhea lead to thiamine deficiency [ 272 ]. Regarding thiamin and exercise, research suggests that thiamin availability in the diet appears to influence exercise capacity when athletes consume the recommended amount [ 254 ].

Riboflavin (B2) is the second vitamin from the B-complex vitamins [ 270 ]. It appears as a yellow-orange chemical molecule that is water-soluble [ 273 ]. Riboflavin is relatively heat- and oxygen-stable, especially in an acidic environment [ 19 ]. It is very light-sensitive, destroyed by reducing agents, and unstable in alkaline solutions [ 4 ]. Riboflavin is essential and must be obtained from food sources [ 2 ]. Riboflavin is abundant in almonds, beef liver, sardines, mushrooms, cheddar cheese, and eggs [ 271 ]. When athletes consume a typical amount of riboflavin, their exercise capability would be optimum [ 254 ].

Niacin (B3) is the third water-soluble member of the B vitamins family [ 176 ]. Humans can partially convert the essential amino acid tryptophan to nicotinamide, which is a dietary supply of niacin [ 270 ]. However, the conversion cannot meet the demands for niacin, so dietary niacin supplies around 50% of the daily niacin requirement [ 256 ]. Meat, whole grains, milk, and dairy products are good sources of niacin [ 242 ]. Niacin is abundant in peanuts, seafood, mushrooms, and yeasts [ 29 ]. Food items high in tryptophan-containing proteins, such as milk, cheese, and eggs, are good sources of niacin [ 7 ]. Its roles include reduction and oxidation (redox) processes, as well as acting as a ligand for a range of purine receptors [ 243 ].

It is hypothesized that this vitamin lowers cholesterol, improves thermoregulation, and improves oxidative metabolism [ 274 ]. In hypercholesteremic individuals, a niacin intake of 100–500 mg/day may help lower blood lipid levels while increasing homocysteine levels [ 176 ]. Nevertheless, consuming 280 mg of niacin during exercise has been demonstrated to reduce exercise capacity by moderating fatty acid mobilization [ 275 ].

Pantothenic acid (B5) is a water-soluble vitamin that is widely available in the diet [ 3 ]. It is often provided as calcium pantothenate, which is more stable against light, heat, and oxygen, but is unstable in both alkaline and acidic circumstances [ 273 ]. Sodium pantothenate is also available, but its use is restricted due to its hygroscopicity [ 272 ]. Pantothenic acid functions as a coenzyme for acetyl coenzyme A (acetyl CoA), implying its importance in aerobic or oxygen-based energy systems [ 2 ]. Acetyl CoA supplementation has not been shown to increase aerobic performance in studies [ 25 , 52 , 202 , 276 ]. Yet, one study found a reduction in the lactic acid buildup, but no benefit in performance was concluded [ 277 ].

Pyridoxine (B6) is marketed as a supplement that increases muscular growth, strength, and aerobic capacity in the lactic acid and oxygen systems [ 141 ]. It might additionally have a relaxing effect, which has been related to increased mental power [ 24 ]. Surprisingly, research showed that pyridoxine did not increase the capacity of aerobic exercise or the accumulation of lactic acid in well-nourished athletes [ 23 ]. However, when paired with vitamins B1 and B12, it has been shown to raise serotonin levels and enhance motor abilities, which are required in sports such as pistol shooting and archery [ 24 ]. Moreover, vitamin B6, thiamin, and pantothenic acid showed inverse relationships with stress risk and anxiety [ 25 ]. Another study revealed that after a month of vitamin B6 intake, young adult athletes reported feeling less anxiety [ 25 ]. Table 2 presents studies that investigated the effect of vitamin B6 intake either as part of a multivitamin supplement or as a sole intake on exercise performance. Most of the studies reported a positive impact on exercise performance, particularly in cases of vitamin B6 deficiency.

Cyano-cobalamin (B1 2) is a coenzyme required for the synthesis of deoxyribonucleic acid (DNA) and serotonin [ 176 ]. In theory, it would enhance muscular mass and blood oxygen-carrying capacity and lessen anxiety [ 273 ]. However, no ergogenic impact has been documented in well-nourished athletes [ 242 ]. Interestingly, it may enhance pistol shooting performance due to the stimulation of serotonin production, which reduces anxiety [ 2 ]. A cross-sectional research work studied 100 amnestic mild cognitive impairment (MCI) patients characterized by low-normal and high-normal vitamin B12 levels, who were then enrolled in an Auditory Verbal Learning test to evaluate their memory’s function. The results showed that those with low-normal B12 concentrations had notable defects in learning and recognition abilities and even in memory performance due to the low microstructure integrity of the hippocampus [ 23 ]. It is important to acknowledge that vitamin B12 is crucial for proper brain functioning, as it aids in faster information processing and enhances concentration levels [ 21 ]. This has been demonstrated in patients with mild cognitive impairment (MCI) who had low-normal levels of vitamin B12 [ 262 ]. This is especially important for athletes, as improved brain functioning may help improve performance in many ways, from learning new techniques to continuous focus maintenance during long competitions [ 24 ].

Folic acid (folate) is a coenzyme that aids in the synthesis of DNA and red blood cells [ 278 ]. An increased red blood cell count enhances oxygen supply to muscles during exercise [ 21 , 79 ]. It is thought to be crucial in preventing birth abnormalities and may lower homocysteine levels, which is a risk factor for heart disease [ 22 ]. Folic acid supplements did not increase exercise performance among malnourished athletes with folate deficiency [ 254 ].

10. Vitamin C

Vitamin C (also known as ascorbic acid) can be found in many types of food, including oranges, strawberries, broccoli, and sweet potatoes [ 15 ]. Athletes require more vitamin C than the average person since their bodies are working harder and being pushed to the limits [ 15 , 279 ]. Therefore, they need to receive enough of this vital nutrient to perform at their best. Researchers have reported that the intake of vitamin C supplements does not boost physical performance in well-nourished athletes [ 52 ]. Nevertheless, athletes are recommended to receive an adequate amount of vitamin C from their balanced diet.

The crucial role of vitamin C in neutralizing free radicals has been raised from its antioxidative potency [ 69 ], thereby improving the immune system [ 15 ] and reducing the risk of illnesses such as colds and other viruses [ 280 ]. It plays an important role in immunity by enhancing the differentiation and proliferation of B and T lymphocytes and increasing antibodies levels [ 25 ]. Furthermore, vitamin C has been reported to modulate cytokine production and decrease histamine levels [ 169 , 281 ]. Studies have also shown that vitamin C can eliminate fatigue, improve coordination, and increase endurance [ 15 ].

Vitamin C has a crucial role to play in wound healing and collagen production [ 3 ]. It helps boost energy levels and protects the body from illnesses and injuries [ 242 ]. Vitamin C works as a co-factor to produce collagen for the propyl and lysol hydroxyls enzymes, which stabilize the structure of collagen [ 29 ]. Furthermore, vitamin C also enhances collagen gene expression in fibroblasts [ 7 ], contributing to the strength and integrity of joints and muscles, which is essential for the success of any athlete. This is supported by the fact that vitamin C is crucial in protecting against ROS damage, enhancing keratinocyte differentiation, lipid synthesis, fibroblast proliferation, and migration, which has been seen to shorten the time of wound healing [ 28 , 282 ].

However, high levels of vitamin C can, in turn, act as a pro-oxidant rather than an antioxidant [ 29 ]. The overconsumption of vitamin C supplement decreases exercise-induced adaptation, delays post-exercise recovery, increases lipid peroxidation, and diminishes mitochondrial biogenesis [ 127 ]. These effects can hinder skeletal muscle adaptation to exercise [ 3 ].

11. Minerals

Numerous physiological and metabolic processes in the human body involve minerals [ 283 ]. Minerals have physiological effects on the body during exercise, including maintaining a normal heartbeat, oxygen transportation, antioxidation activity, healthy bone, and immune system enhancement [ 283 ]. Sufficient levels of minerals are required for optimal performance because many of these processes are enhanced during sports activity [ 284 ]. For athletes to perform at their best, maintaining a healthy body necessitates the intake of a variety of nutrients. Some minerals make weightlifting more effective by enhancing athletic performance; these are the minerals that degrade faster when used in sports endeavors [ 285 ] and thus need to be replaced routinely among athletes to sustain their performance. Table 1 summarized the recommendation requirements of minerals along with the rich sources and their roles in exercise performance.

Iron (Fe) is a crucial mineral for physical performance, and its importance cannot be overstated [ 286 ]. When it comes to peak performance, an adequate intake of iron can make all the difference [ 149 ]. It helps the body produce red blood cells, which are necessary for transporting oxygen to the muscles [ 71 ]. Without enough iron, athletes and other physically active individuals may suffer from fatigue and lethargy as the body struggles to meet the increased demands [ 71 ]. A huge part of the pool of plasma iron (almost 80%) is utilized by the bone marrow; this is equivalent to a 20–30 mg/day dose to ensure the efficient production of erythrocyte [ 31 ].

In addition to red blood cells production, iron is also important for energy metabolism [ 31 ]. It is necessary for converting food into energy, and it helps to ensure that the body can use energy efficiently for physical activities [ 280 ]. Iron also helps the body in regulating its temperature, making it an essential nutrient for athletes competing in warm climates or hot weather [ 149 ]. Finally, it is important for other bodily functions, such as the immune system, growth, and hormone production [ 284 ]. When considering physical performance, it is important to ensure that iron intake is adequate and balanced. The human physiological mechanism preserves the maximum iron [ 29 ]. Based on the total compulsory iron depletion that occurs daily and the average of 10% absorption and bioavailability, the World Health Organization (WHO) and other national institutes have estimated iron-recommended doses depending on several characteristics including gender, age, and race. The recommended dietary intake for females is 18 mg, and for males, it is 8 mg [ 31 ]. Poorly planned diets, coupled with inadequate levels of exercise, can lead to anemia and other problems associated with low iron levels [ 286 ]. This may cause fatigue, poor performance, and a decreased ability to perform physical activities [ 285 ]. Therefore, it is necessary to consume a high-quality variant diet that involves iron-rich sources [ 284 ].

It is also important to make sure that athletes have enough time to rest and recover between workouts. Iron helps to replenish energy stores and reduce fatigue, so it is important to give the body time to absorb the nutrient [ 287 ]. Additionally, certain supplements may also help in providing additional iron to meet the demands of physical performance [ 205 ]. Athletic training can result in alterations including higher vascularization (creation of new blood vessels), elevated hematocrit, and higher erythrocyte awareness in the blood, which may lead to an increase in iron needs [ 122 ]. A shortage of iron may result from hemorrhages, gastric blood loss, and/or urinary tract bleeding, especially among high-intensity sports [ 121 ]. Professionals are predicted to have 70% higher iron needs than non-professionals [ 287 ]. Iron deficiency anemia can impede progress in an athlete’s training by reducing oxygen delivery [ 283 ]. Lastly, most research concluded that iron supplements do not enhance aerobic performance, unless there is a specific depletion and/or anemia reported [ 149 ].

13. Calcium

Athletes must be in peak physical condition to perform at their best and make sure their diets are balanced, which is an important part of their training regimen [ 288 ]. Calcium (Ca) is among the many nutrients that athletes need to remain healthy [ 289 ]. It not only helps to keep bones and muscles strong, but it has also been linked to improved performance in athletes [ 32 ]. However, insufficient Ca consumption and elevated Ca depletion may expose a person to osteoporosis [ 194 ]. Athletes should make sure to consume an adequate amount of Ca each day as part of their balanced diet, which would achieve around 1500 mg/d [ 32 , 188 ]. The optimal Ca requirement is 1200 mg/day for adolescents and youth, 1000 mg/day for females aged 25 to 50 years old, and 1500 mg/day for postmenopausal females who are not treated with estrogen replacement therapy [ 33 ]. With the right diet and exercise routine, they may capitalize on the benefits that Ca has to offer and maximize their performance [ 32 , 188 ].

Numerous studies have indicated that the adequate and consistent consumption of Ca can potentially enhance physical performance in athletes [ 289 ], as it plays a crucial role in maintaining muscle strength, which is a key element for exercise performance [ 35 , 289 ]. Additionally, it may help reduce injuries and improve recovery time [ 32 ]. It is also known that Ca may protect the bones and joints from stress caused by continuous physical activity [ 32 ]. Conversely, improving Ca status with 2000 mg of Ca supplementation has been shown to reduce the risk of developing a stress fracture [ 289 ]. Calcium also helps to convert carbohydrates and fat into energy, which can contribute to performance improvement [ 78 , 288 ]. It also helps in reducing fatigue and delaying the onset of muscle soreness [ 290 ].

Calcium can be found in many common foods including milk, yogurt, cheese, and dark leafy greens. Other sources include tofu, nuts, fish, and fortified cereals [ 289 ]. Additionally, athletes may consider Ca supplements if they are unable to receive the recommended daily intake from their diet. It is important to note that the amount of Ca an athlete needs daily may vary depending on their weight and activity level [ 289 ]. Skeletal muscles’ ability to contract and relax depends in part on Ca [ 291 ]. The importance of it binding to troponin C for the contraction of muscles has the potential to influence performance [ 33 ]. While it is true that training leads to higher Ca loss, primarily through perspiration, the foundations of bone mineralization are Ca, vitamin D, and physical activity [ 292 ]. However, in rare circumstances, especially if the diet is low in its nutrient density, physical activity might endanger bones [ 65 ]. Every athlete should place a high priority on developing and maintaining optimal bone health, since vigorous physical activity increases the stress fractures risk [ 85 , 188 ].

14. Potassium

When it comes to athletes’ health and performance, one mineral that is essential to success is potassium (K) [ 293 ]. It is a required nutrient for human health and is necessary for many physiological processes [ 293 ]. Adults should not exceed the consumption of 2000 mg sodium/day (Na) or 5 g of salt and have a minimum dose of 3510 mg potassium/day, according to new guidelines established by the WHO [ 14 , 281 ]. It has a crucial role in muscle contractions and helps the body regulate fluid balance, blood pressure, and the heart rate [ 281 ]. In addition to its role in muscle contractions, it is also involved in nerve functions and proper electrolyte balance [ 59 ], which may be beneficial to athletes who may be sweating during a long practice or game [ 29 ]. Furthermore, proper potassium levels can help prevent injuries and help athletes maintain their energy levels [ 177 , 230 ].

Potassium is a great source of energy for athletes [ 293 ]. It helps to reduce the amount of lactic acid stored in the muscles [ 59 ], which may lead to fatigue as well as maintain a healthy metabolism [ 35 ]. It is also involved in the breakdown of carbohydrates, which helps keep energy levels high during intense physical activity [ 177 ]. It is unknown if potassium supplementation reduces the occurrence of muscular cramping in athletes. It should be acknowledged that there have been no reports of ergogenic effects [ 58 ].

15. Magnesium

Magnesium (Mg) is an essential mineral that is recognized for its critical role in athletic performance and overall health [ 294 ]. Magnesium helps to improve energy levels, reduce fatigue, and even increase muscle performance, making it a vital nutrient for athletes [ 36 ]. With its numerous benefits, magnesium is being increasingly taken by athletes to help them reach peak performance and maintain their physical health [ 294 ]. Magnesium helps to improve energy levels by raising the ATP availability, which is best defined as the gold energy stores of cells [ 283 ]. Deficiency may cause ATP levels to be depleted, resulting in fatigue and overall reduced performance [ 34 ]. The regular consumption of Mg can improve ATP production, providing athletes with increased energy and improved endurance [ 295 ]. The mineral is also important for maintaining muscle performance and reducing fatigue [ 296 ]. It is known to support muscle contraction and relaxation, allowing for better muscle control and improved performance [ 142 ]. It also works to reduce lactic acid buildup in muscles, which may help reduce pain during exercise and improve recovery time [ 297 ].

Moreover, Mg has numerous other benefits that support physical wellbeing. It helps to improve sleep quality, regulate blood sugar, reduce stress, and even support the cardiovascular system [ 294 , 297 ]. By regularly taking Mg, athletes may benefit from improved energy production, reduced fatigue, and improved physical health, allowing them to reach their maximum performance potential [ 36 ]. The Recommended Dietary Allowance (RDA) is 400 to 420 and 310 to 320 mg/day for 14 to over 70 years of age among males and females, respectively [ 294 ].

Magnesium is a versatile mineral that is important for recovery and is found in over 300 enzymes that are involved in energy metabolism [ 297 ]. It is linked to strength training and cardiorespiratory processes, showing a reciprocal relationship between exercise and Mg in the human body [ 142 ]. Exercise controls Mg distribution and usage [ 296 ]. Training triggers Mg to be transferred to areas where energy is produced [ 37 ]. For instance, during prolonged activity, serum Mg may be transferred from serum blood to red blood cells (RBCs) or muscle to support exercise. On the other hand, short-term exercise may result in a reduction in the plasma/serum volume and a rise in serum Mg levels [ 297 ].

Magnesium contributes to the metabolism of energy and supports typical muscular contraction and relaxation [ 283 ]. In male athletes, serum Mg levels are favorably correlated with muscular performance [ 36 ]. Additionally, research suggests a possible connection between Mg deficit and muscle cramps by demonstrating how it might alter neuromuscular function [ 297 ]. Physically active people might need more magnesium to sustain their peak exercise performance than inactive people do [ 283 ]. Low Mg levels may cause ineffective energy metabolism and decreased endurance in individuals who are engaged in a weight training program [ 294 ]. Higher Mg consumption is linked to enhanced cardiorespiratory function and lower oxygen demand during aerobic exercise [ 34 ]. Most studies reported little impact of 500 mg/day Mg on exercise performance in athletes, unless there is a deficit [ 37 , 142 , 296 ]. A study of 16 physically active men who were assigned to 300 mg/day for 14 days of Mg supplementation or a control group concluded no direct impact on exercise performance while using Mg supplementation [ 296 ].

Athletes of all ages and skill levels rely on zinc (Zn) to keep their bodies performing at their peak [ 298 ]. It is an essential mineral that our bodies need for metabolic functions such as cell repair, immune system functioning, hormone production, and healthy skin [ 38 ]. Unfortunately, not all athletes receive enough zinc from food intake, which may leave athletes at a disadvantage [ 38 ]. According to the UK National Diet and Nutrition Survey (NDNS), current daily intakes are 9.5 mg and 7.6 mg for men and women, respectively [ 299 ]. The survey has also shown that 6% of men and 7% of women do not receive enough zinc in their diet, putting them at a greater risk of deficiency [ 300 ]. Fortunately, there are many benefits athletes may reap from adding zinc supplements to their routines [ 300 ].

One notable benefit of zinc supplementation is the improvement in athletic performance [ 281 ], as it reduces blood viscosity and enhances oxygen delivery, thereby boosting aerobic endurance [ 38 , 281 ]. Zinc helps to increase strength and endurance, so athletes may push their bodies to the limit while still receiving the nutrients they need [ 298 ]. A double-blinded cross-over study featuring 16 female athletes was conducted to estimate muscle strength and endurance [ 38 ]. The participants consumed 135 mg/day of Zn for 14 days and showed remarkably higher dynamic isokinetic strength and angular speed [ 29 ]. Additionally, Zn may help to reduce inflammation and soreness, which can accelerate recovery time and reduce the risk of injury [ 59 ]. Zinc may also help in improving attention and focus [ 60 ]. This can assist athletes in staying focused on their tasks and performing at their best. Zinc is a vital mineral for athletes of all ages and abilities [ 273 ]. Including it as a supplement to their regimen may help enhance strength, endurance, and focus while also reducing inflammation and supporting the immune system [ 92 ].

In addition, Zn may help to boost the immune system, making it easier for athletes to fight off colds and other illnesses that can stall their progress by increasing neutrophils’ ability to produce ROS after exercise [ 7 ]. It has been indicated that Zn oral consumption of 25 mg/day while exercising can reduce exercise-induced changes in immune function to the minimum [ 298 ]. Moreover, Zn may help support healthy vision and keep skin healthy, both of which are important for optimal performance [ 258 ]. Zn impacts the formation and efficient functioning of the skin and mucous membranes [ 298 ]. It helps maintain skin cell membranes, and it plays a part in cell mitosis and differentiation; moreover, it has an essential role in the survival of keratinocytes [ 215 ] and even in protecting skin against induced UV radiation damage [ 301 ]. Lastly, taking Zn supplements may help athletes meet their nutritional goals without having to increase their caloric intake, making it an ideal supplement for those who are trying to stay lean [ 6 ]. Despite Zn supplements being popular among athletes, there is limited proof regarding athletic performance improvement in a period of 1–6 weeks, as shown in the study of Polat, 2011 [ 302 ].

To detect the actual impact of zinc oral consumption on the hematological parameters, a study included 24 male kickboxing athletes, who were separated to form the three following groups: the EZ group, meaning they were exercising and consuming 2.5 mg/kg Zn supplement daily; the SZ group, who were supplemented without exercising; and the E group, who were exercising without being supplemented. After the period of 8 weeks, the results showed a significant increase in the erythrocyte count of the EZ group compared to the two other groups ( p < 0.001). The hemoglobin and hematocrit levels increased in the EZ group ( p < 0.05). These results revealed that the combination of exercise and Zn supplementation has a beneficial impact on the hematological parameters of athletes, which may result in enhanced performance and increased stamina [ 303 ]. Low levels of Zn in the muscles may diminish exercise endurance because it is necessary for the activity of energy metabolism enzymes [ 304 ]. Due to the influence of this enzyme on skeletal muscular exercise, lactic dehydrogenase (a Zn-containing enzyme) may facilitate the conversion of lactic acid to pyruvate [ 38 ]. This finding contradicts the commonly misinterpreted results of previous studies [ 59 , 303 ], which demonstrated that lactate accumulation does not directly cause fatigue [ 305 ].

17. Selenium

One possible approach for athletes to achieve their goals is by including selenium (Se) in their diet, as this mineral can be found in a variety of foods [ 40 ]. Selenium, when consumed in proper amounts, will help to boost an athlete’s performance, improve mental focus, and reduce inflammation, thereby contributing to overall health and fitness [ 40 , 41 , 257 ].

Selenium can be found in certain plant and animal products, and it may also be artificially added to processed foods [ 42 ]. It is advantageous for athletes due to its powerful antioxidant characteristics that boost the body’s defenses against cell damage, hence increasing endurance, strength, and overall performance [ 40 ]. Additionally, Se may increase mental focus, which improves an athlete’s ability to concentrate on tasks and stay motivated, even if the competition gets tougher [ 41 ]. It can also help to reduce levels of inflammation and support anti-inflammatory mechanisms, which may boost recovery times and minimize the risk of injuries [ 95 ]. Low levels of serum Se are associated with high serum levels of C-reactive protein (CRP), the inflammation biomarker [ 306 ] It is well addressed that Se increases glutathione peroxidase production, which prevents the effect of oxidative stress in response to exercise [ 303 ]. On the other hand, Se deficiency reduces glutathione peroxidase activity indirectly through controlling the Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-κB) [ 257 , 307 ]. In the CHIANTI cohort study that assessed coordination performances among 1012 candidates aged 65 years or older, the authors found a reduction in neurological performance that was significantly associated with the low levels of Se [ 308 ].

Incorporating Se into an athlete’s diet may be as simple as consuming more foods that are naturally rich in Se or taking it in supplemental form. When consuming the recommended amounts, it may increase the overall health and performance of athletes [ 306 , 307 , 309 ]. Induced excessive mitochondrial oxidative stress could be caused by Se supplements overdose and may lead to serious health problems [ 273 ] marked by organelle damage and dysfunction [ 310 ]. Hence, it is important to integrate it into a balanced diet in appropriate doses rather than consuming mega doses [ 311 ]. A systematic review of oral Se supplementation of 180 µg/day or 240 µg/day ( selenium methionine ) and 200 µg/day ( Sodium Selenite ) reported a significant drop in lipid hydroperoxide levels and an increase in glutathione peroxidase (GPx) in plasma, erythrocyte, and muscle [ 306 ]. The authors concluded that the consumption of Se supplements has no impact on aerobic or anaerobic performance [ 306 ]. In addition, the study revealed that Se supplementation may inhibit Se deficiencies induced by high-volume and -intensity exercise, but it has no impact on anaerobic and aerobic athletic performance as well as creatine kinase activity, exercise training-induced adaptations, and testosterone hormone levels [ 303 , 306 ].

18. Manganese

As athletes struggle to achieve their best performance, they often look to improve their health and performance. One mineral that has been gaining recognition for its potential benefits is manganese (Mn) [ 312 ]. Mn is essential for several bodily functions, including energy production, bone formation, and enzyme activity [ 264 ]. Early studies have shown that it may help improve various aspects of athlete health and performance, but little is known about the exact benefits of Mn for athletes [ 205 , 303 ].

Manganese plays an important role in energy production, as it is involved in the breaking-down of carbohydrates, proteins, and fats needed for energy production [ 205 ]. It also helps the body to utilize energy more efficiently, which may result in improved endurance during long-term workouts and competitions [ 304 ]. Additionally, it aids in the production of important neurotransmitters, which may improve mental focus and coordination during physical activities [ 304 ]. Due to its crucial role in bone formation, several studies reported the relationship between Mn and bone health [ 43 ] It helps in the development of strong and healthy bones [ 43 ], which is crucial for athletes to prevent injury and speed up recovery time. Low serum Mn levels have been reported among osteoporotic women compared to healthy subjects [ 312 ]. Studies have also suggested that Mn helps to protect cells from damage caused by ROS, which is important during periods of strenuous exercise [ 95 , 304 ]. It is crucial for scavenging ROS in mitochondrial oxidative stress, as it involves the Mn superoxide dismutase (MnSOD) component [ 95 ].

In a clinical trial, it was found that athletes had significantly higher concentrations of basal Mn levels vs. sedentary individuals, as observed through blood and urine measurements [ 7 ]. Conversely, sedentary participants exhibited higher urine levels of Mn, which could be attributed to the possibility of iron deficiency in athletes, leading to increased Mn absorption [ 313 ]. There is limited evidence regarding Mn and athletic performance; however, athletes should be evaluated periodically for micronutrients deficiencies. Although more research needs to be conducted, the current evidence suggested that Mn may be beneficial for athletes who are looking to optimize their performance and health [ 205 , 304 ]. Adding Mn to an athlete’s diet could be useful for maximizing their performance [ 95 ].

19. Micronutrients Deficiency and Energy Deficiency’s Impact on an Athlete’s Performance

Pathways for utilizing energy are significantly influenced by vitamins and minerals [ 93 ]. A variety of physiological systems depend on micronutrients, which also have an impact on general health and athletic performance [ 23 ]. According to the widespread opinion on dietary guidelines for sports, a healthy athlete does not need to exceed RDA values if they consume an adequate number of nutrient-dense foods [ 267 ]. Unfortunately, many athletes do not meet the RDA requirements for most micronutrients [ 6 , 267 ]. Micronutrients would logically be impacted by poor macronutrient consumption [ 25 ]. It is common among many athletes who are not aware about their exercise energy demands and, on the contrary, suffer from being on a negative energy balance [ 2 ]. Negative energy balance due to increased or decreased calorie intake or a combination of both is a powerful disruptor of the endocrine milieu [ 123 ]. Additionally, it was associated with increased fatigue and mental disorders [ 14 ], reduced fertility, poor bone quality, a higher likelihood of sports injuries, endothelial dysfunction, a poor lipid profile, gastrointestinal disturbances, inflammatory processes, psychiatric conditions (such as emotional state changes/irritability), and poor athletic performance [ 93 , 108 , 154 , 314 ].

One common energy deficiency condition among athletes is the female athlete triad, characterized by disordered eating, negative energy balance, and irregular or absent menstrual cycles [ 315 ]. This condition predisposes women to menstrual dysfunction (amenorrhea) [ 316 ], diminished bone mineral density, and premature osteoporosis [ 45 ]. Each defect of the triad represents a significant medical concern, and if occurring together, the possibility of health concerns becomes even more serious and can often cause potential threats to life [ 317 ]. Medical adverse consequences associated with disordered eating involve decreased levels of glycogen in its stores, reduced lean body mass, long-term fatigue, dehydration, micronutrient deficiencies, electrolyte and acid-base imbalances, anemia, gastrointestinal diseases, parotid gland enlargement, reduced bone density, and tooth enamel erosion [ 300 ]. Osteoporosis can make adolescent female athletes prone to early bone loss and the improper formation of bone, resulting in low bone mineral density [ 318 ] and an elevated risk of stress fractures [ 319 ]. Bone mineral density lost because of amenorrhea may be totally or, at least partially, irreversible, even with the resumption of menses, calcium supplementation, and estrogen replacement therapy [ 256 , 320 ]. The dispensable role of supplementary vitamins and minerals is a concern of the Dietitians of Canada and the American College of Sports Medicine (ACSM) for ensuring adequate energy requirements are met from a varied and balanced diet with supplementations enrichment. Equally importantly, sports medicine experts may recommend the use of vitamin and mineral supplements in specific conditions such as energy intake restriction, the adoption of a plant-based diet, the presence of illness, or recovery from injuries [ 242 , 263 , 301 , 321 , 322 ]. It is worth noting that individual needs vary, and a personalized approach is crucial when making supplement recommendations.

20. Conclusions

Vitamins and minerals are crucial for an athlete’s health and performance, none more so than others. Micronutrients are essential to achieving optimal health and performance. They participate in many metabolic processes in the body, including energy production, muscle growth, and recovery. Athletes need to ensure they consume sufficient quantities of micronutrients to improve their physical activity and performance. A balanced diet that includes a variety of fruits, vegetables, whole grains, and lean proteins may help them meet their micronutrient needs. Additionally, they may benefit from taking a multivitamin supplement if they are not meeting their micronutrient requirements or suffer from malabsorption or specific deficiencies in certain vitamins. However, athletes must avoid taking micronutrient supplements without first ensuring there is a deficiency. It is important to consult with a physician or a dietitian to determine if supplementation is necessary and to obtain a proper prescription.

Abbreviations

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This research received no external funding.

Author Contributions

Conceptualization, H.J. and H.A.G.; Methodology, H.J.; Software, H.J.; Formal Analysis, H.J.; Writing—Original Draft Preparation, M.A.H., K.M.R., K.K.A., R.O.A., M.J., S.A. and R.A.A.; Writing—Review & Editing, H.A.G., K.T. and H.J.; Funding Acquisition, not applicable. All authors have read and agreed to the published version of the manuscript.

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• Case Report
• Open access
• Published: 05 June 2024

Aberrant left coronary artery from the pulmonary artery with patent ductus arteriosus - a case report and review of the literature

• Ahmad Amer   ORCID: orcid.org/0000-0002-1626-302X 1 , 2 ,
• Hanita Shai 1 , 2 ,
• Sagi Assa 1 , 2 ,
• Avital Mitler 1 , 2 &
• Alona Raucher Sternfeld 1 , 2  

Journal of Cardiothoracic Surgery volume  19 , Article number:  319 ( 2024 ) Cite this article

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Aberrant left coronary artery from pulmonary artery (ALCAPA) is a very rare congenital heart defect. Its coexistence with patent ductus arteriosus (PDA) is extremely rare. The high pressures created by the left-to-right shunt in the pulmonary arteries can delay symptoms and create a real challenge in diagnosing ALCAPA. Missing this diagnosis can have severe results, including extensive ischemia and sudden death.

Case presentation

We present a case of an infant born with a large PDA. Initially treated conservatively, however, due to congestive heart failure and lack of weight gain, she underwent surgical ligation of the PDA at the age of four and a half months. Following surgery, she developed pulmonary edema. Echocardiography revealed decreased ventricular function. ECG revealed ST elevations on lateral leads, and serum troponin was significantly increased. The patient underwent cardiac magnetic resonance imaging (MRI), which revealed signs of wall ischemia and decreased function of the left ventricle (LV) with unclear coronary anatomy. Diagnostic catheterization revealed an ALCAPA. She underwent surgical intervention, and the left coronary artery was re-implanted in the aortic sinus. Follow-up revealed slow improvement of cardiac function.

Discussion and literature review

The coexistence of PDA and ALCAPA is a very rare occurrence. We found at least 10 reported cases in the literature. Delayed diagnosis might be detrimental. The prognosis of these patients is variable.

An unusual post-surgical course following PDA repair requires a high index of suspicion and appropriate evaluation for ALCAPA, preferably with angiography.

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ALCAPA, also known as Bland-White-Garland syndrome, is a rare coronary abnormality, constituting 0.3–0.5% of congenital heart defects [ 1 , 2 , 3 ]. Left untreated, it can cause mortality in 90% of cases [ 2 , 3 ]. Survival into adulthood is probably due to collateral development in the coronary circulation, with the risk of sudden death remaining high [ 4 , 5 , 6 ].

ALCAPA is, in most cases, an isolated defect, but in rare incidences, it has been described with other anomalies like tetralogy of Fallot, coarctation of the aorta, ventricular septal defects, and PDA ( 7 – 8 ).

ALCAPA is asymptomatic in the fetal period, as the pressures and oxygen saturations are similar in the great arteries. Following birth, the pressure in the pulmonary artery gradually decreases to a point where the coronary perfusion pressure, that is the difference between the pressure in the coronary artery and the LV wall pressure, is not adequate and ischemia ensues. This, in turn, causes dysfunction of the left ventricle, dilation of the left side of the heart, and mitral regurgitation, reflected as clinical heart failure and, in some cases, arrhythmias and sudden death [ 1 , 9 ].

We report a case of ALCAPA masked by a large PDA in an infant female. Informed consentwas acquired from the patient’s guardian for this report.

A female infant was born with a large PDA. She developed early congestive heart failure and was initially treated conservatively with diuretics, ACE inhibitors, and high-caloric feeding, and followed up in the pediatric cardiology clinic.

Repeat echocardiography showed a PDA 4–5 mm in diameter with a left-to-right shunt across and a low-pressure gradient. The left atrium, left ventricle, and pulmonary arteries were all dilated, as expected. Cardiac function was normal and hyperdynamic in some tests. The coronaries were reported to be normal in origin and course in multiple tests by experienced sonographists and pediatric cardiologists (Fig. 1 ).

The original management plan was to allow the patient to gain enough weight, making trans-catheter device occlusion of the PDA feasible. However, weekly follow-ups indicated worsening congestive heart failure, reflected by failure to thrive as well as recurrent respiratory infections requiring hospitalization.

Following prolonged hospitalization due to RSV bronchiolitis at the age of 4 months and the persistent lack of weight gain, it was decided to perform surgical ligation of the PDA. At the age of 4.5 months, the PDA was ligated through a lateral thoracic incision with an unremarkable surgical course.

Following surgery, on post-surgical day (POD) 2, the patient was weaned off mechanical ventilation and catecholamine support. However, dyspnea, tachypnea, and tachycardia persisted. Chest X-ray on POD 3 revealed worsening congestion. Additionally, the ECG which had been normal up to POD 2, began to exhibit pronounced ST elevations on anterior and lateral leads on POD 3 and 4 (Fig. 2 ). Echocardiography revealed significantly decreased left ventricle function, assessed through “eyeballing” and fractional shortening measurement of 10–15%. Echocardiography did not explain the findings; the coronary anatomy was investigated thoroughly by multiple pediatric cardiologists and reported as normal. Troponin was measured and found to be significantly increased, reaching a maximum of 5330 ng/L.

A differential diagnosis was suggested, including an iatrogenic surgical cause, infectious myocarditis, and coronary anomalies missed in the echocardiography.

Following an extensive interdisciplinary consultation, during which the possibility of conducting further diagnostic tests such as computed tomography (CT) imaging was entertained, it was ultimately determined that pursuing a cardiac magnetic resonance imaging (MRI) examination would offer the most clinically informative approach, particularly in the context of the complex array of potential differential diagnoses under consideration. Subsequently, on POD 6,the patient underwent a cardiac MRI, which revealed thinning of the myocardium and hypokinesia of the lateral wall and septum, increased T2- weighted signal indicating edema, and late gadolinium enhancement of the endocardium (Fig. 3 – 4 ). The left ventricle and atrium were dilated, with a left ventricular ejection fraction measured at 20%. The coronary anatomy was not clear.

On POD 7, she underwent pulmonary artery angiography, confirming the diagnosis of ALCAPA (Fig. 5 ).

She underwent emergent surgical intervention on the same day, during which the left coronary artery was successfully re-implanted in the aortic sinus. The surgery was without complications. She was weaned off cardiopulmonary pump easily and transferred to the pediatric intensive care unit (PICU).

Following surgery, she had a prolonged course due to decreased LV function. Extubation was performed on POD 5, and she was completely weaned off catecholamine support by POD 12. Her PICU length of stay was 25 days, and the total length of stay was 30 days. Prior to discharge, troponin decreased to 358 ng/L, and echocardiography revealed some improvement of cardiac function.

Since her discharge, seven months ago as of the writing of this report, she has been re-hospitalized a total of 7 times. The first re-hospitalization has been just 5 days following her discharge. Most readmissions were due to social factors; however, in two cases, she had respiratory infections with decompensation of her heart failure requiring PICU hospitalization.

Follow-up revealed slow and gradual improvement of cardiac function with wall motion abnormalities and dilated cardiomyopathy. Due to slow improvement, she completed a coronary CT and invasive angiography, both demonstrated patent coronaries arising from the aorta. Her last follow-up was at the age of eleven months, seven months following surgery. She appears well with only mild tachypnea and is gaining weight slowly. Echocardiography revealed dilated LV and left atrium, lateral and septal wall motion abnormalities, and fractional shortening of 23%. The re-implanted left coronary artery appeared patent with normal flow. She continues medical treatment and receives furosemide, captopril, and digoxin, which she tolerates well.

The combination of ALCAPA and PDA is extremely rare. One paper by Wesselhoeft et al., reviewing 140 cases of ALCAPA, found only one case associated with PDA [ 9 ].

The pathophysiology of ALCAPA is usually a gradual decrease of blood supply to the myocardium as the pulmonary pressure decreases following birth [ 9 ].

The presence of a sizable arterial duct with a large shunt into the pulmonary artery increases the pressure in the vessel which in turn sustains sufficient perfusion to the left coronary artery, consequently delaying clinical presentation until the duct is ligated [ 10 ]. The combination of PDA and ALCAPA is thus gravely dangerous, as the PDA not only complicates the diagnosis of ALCAPA but can also produce catastrophic ischemia when it is repaired ( 11 – 10 , 12 ).

We reviewed the literature for all available publications reporting on a combination of PDA and ALCAPA in infants. We searched PubMed for the terms PDA AND ALCAPA and augmented our search with Google Scholar and the regular Google search engine. We chose to omit adult cases, given that the pathophysiology might be different. We found at least 10 reported cases in the literature, which are presented in Table  1 .

Most infants initially present with congestive heart failure (CHF) in the first months of life. All cases, including ours, report normal LV function in the initial presentation; some have mitral regurgitation (MR), which, along with the CHF, is attributed to the large PDA. A specific finding of hyperechoic papillary muscle was reported in four of the ten cases [ 12 , 16 , 17 , 18 ].

ALCAPA was recognized in three cases prior to surgery. In two cases, it was recognized incidentally during diagnostic catheterization [ 13 , 17 ]. In the third case, it was diagnosed by transthoracic echocardiography (TTE) [ 16 ].

The clinical presentation following PDA closure is dramatic in all cases. Most develop immediate hemodynamic shock or ventricular arrhythmia [ 12 , 14 , 18 , 19 ], and some develop CHF with severely decreased LV function ( 11 – 10 , 15 ). The diagnosis of ALCAPA following PDA repair might be delayed, especially in cases with a non-catastrophic presentation. In one case, the diagnosis was delayed for 2 years [ 11 ]; however, this was an out-of-country case where the local staff might have had limited resources. In another case, the infant improved clinically following PDA closure, and the diagnosis was only made 16 days following the surgery during a routine TTE [ 15 ]. In our case, the patient didn’t present dramatically following the PDA closure. As mentioned, she was weaned off catecholamine support and invasive ventilation and developed pulmonary edema on POD 3 and 4. This relatively mild course might have contributed to the delay in the diagnosis.

Angiography remains the gold standard for ALCAPA diagnosis; this is also reflected in the cases described in this paper. TTE can be very effective in finding this diagnosis, but the combination with PDA might limit its utility. This observation may be attributed to the substantial jet generated by the PDA into the pulmonary artery, along with the normal flow direction in the aberrant coronary artery [ 8 ]. In our case, apart from TTE, the first modality chosen was cardiac MRI. This was to rule out other considered diagnoses, specifically myocarditis. MRI use is not common in this context. In our case, though it didn’t directly reveal the ALCAPA, it strongly suggested it, and the diagnosis was finalized via angiography as mentioned before.

The prognosis of these patients is variable. Three patients died: one was diagnosed with a significant delay of two years and didn’t survive the surgery [ 11 ], another, diagnosed on POD 2 after duct ligation, also didn’t survive the re-implantation procedure [ 10 ]. Both of these cases are from the 80s; surgical and anesthesia techniques and expertise have evolved since. The third case of mortality described an infant with severe comorbidity, a hypoplastic aortic arch, who was diagnosed in the operating room following weaning off bypass; he also didn’t survive the surgery [ 19 ].

For surviving patients, prognosis appears to be good, although it was only described in four of the seven living cases [ 12 , 15 , 17 , 18 ]. The long-term prognosis of patients with isolated ALCAPA is reported to be good [ 20 , 21 ]. A large series describing more than 100 patients four years after corrective surgery reported very low mortality and normalization of the LV function in almost all patients [ 21 ].

In our case, seven months after surgical repair, the patient unfortunately continues to have a dilated LV with decreased fractional shortening, however, she is gaining weight gradually and managed mostly in the ambulatory setting.

The combination of ALCAPA and PDA carries a special risk. High awareness must be maintained, and any clues for the diagnosis have to be fully pursued prior to PDA repair. An unusual post-surgical course following PDA repair requires a high index of suspicion and immediate appropriate evaluation for ALCAPA, preferably with angiography.

Coronary echocardiographic imaging prior to surgery

ECG on POD 4revealing ST segment elevations

Cardiac MRI scan T2-weighted signal- Lateral LV wall edema

Cardiac MRI scan - Diffuse LV late gadolinium enhancement

Pulmonary artery angiography – LMCA arising from the pulmonary artery

Data availability

No datasets were generated or analysed during the current study.

Abbreviations

Aberrant Left Coronary Artery from Pulmonary Artery

Congenital Heart Disease

Ventricular Septal Defect

Patent Ductus Arteriosus

Left Ventricle

Transthoracic Echocardiography

Pediatric Intensive Care Unit

Post-Operative Day

Congestive Heart Failure

Mitral Regurgitation

Left Main Coronary Artery

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Ahmad Amer, Hanita Shai, Sagi Assa, Avital Mitler & Alona Raucher Sternfeld

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A.A. wrote and edited manuscript H.S. provided imaging insight and prepared the MRI imaging and reviewed the text S.A. provided invasive catheterization insight and image and reviewed the text A.M. helped research the literature. A.R. supervised and reviewed the text.

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Amer, A., Shai, H., Assa, S. et al. Aberrant left coronary artery from the pulmonary artery with patent ductus arteriosus - a case report and review of the literature. J Cardiothorac Surg 19 , 319 (2024). https://doi.org/10.1186/s13019-024-02803-x

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Ochrobactrum anthropi infection following corneal transplantation -a case report and review of literature

• Lei Liu 1 ,
• Chunmei Wang 1 ,
• Lulu Hou 1 ,
• Rong Huang 1 ,
• Xiaoru Shi 1 &
• Hui Jia 1  

BMC Ophthalmology volume  24 , Article number:  234 ( 2024 ) Cite this article

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Ochrobactrum anthropi is widely distributed and primarily infects patients with compromised immune functions . Historically, O. anthropi has been considered to possess low toxicity and pathogenicity; however, recent studies suggest that it may in fact cause severe purulent infections. In this case study, we examine a case of O. anthropi infection following corneal transplantation, exploring the occurrence and outcomes of such post-operative infections.

Case presentation

A retrospective analysis of cases involved examinations, genetic testing for diagnosis, and subsequent treatment. In patients undergoing partial penetrating keratoplasty with a fungal corneal ulcer perforation, anterior chamber exudation and purulence were observed post-surgery. Despite antifungal treatment, genetic testing of the anterior chamber fluid and purulent material confirmed O. anthropi infection. The use of antimicrobial treatment specifically targeting O. anthropi was found to be effective in treating the infection.

Inflammatory reactions following corneal transplantation should be should be monitored for the presence of other infections. Genetic testing has significant implications for clinical diagnosis and treatment.

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Introduction

Ochrobactrum anthropi, a conditional pathogenic bacterium, is a Gram-negative rod that exhibits oxidase and catalase production and lacks fermentation capability. It is widely distributed and primarily infects patients with compromised immune functions [ 1 , 2 ]. Reports also indicate infections in hosts without prior illnesses and with normal immune functions [ 3 , 4 ]. The clinical presentation of infections caused by O. anthropi is not specific and the bacteria demonstrates robust drug resistance. This poses challenges in clinical diagnosis and treatment [ 5 ].

Historically, Ochrobactrum anthropi has been regarded as having low toxicity and pathogenicity. However, it can cause severe purulent infection [ 6 ]. Reports exist of post-organ transplantation bacteremia [ 7 ], and in ophthalmology, occurrences of intraocular inflammation following cataract surgery [ 8 , 9 ]. However, cases of O. anthropi infection after corneal transplantation have not been documented. Here, we present a case of O. anthropi infection following corneal transplantation surgery.

Case report

A 51-year-old male patient presented with a 19-day history of redness and pain in the eye. The diagnosis was fungal keratitis (Fig. 1 ). Treatment included frequent instillation of natamycin eye drops (50mg/ml, North China Pharmaceutical, China) and intermittent application of intracorneal voriconazole injection (1mg/ml, Pfizer Limited, US). Following one month of treatment, examination results indicated that the sign of corneal ulcer healing, with no observable progress. However, there was a concerning sign of corneal perforation. (Fig. 2 ). B-ultrasound demonstrated the absence of abnormalities in the vitreous and retina. Consequently, a partial penetrating keratoplasty was performed with a favorable outcome. Intraoperatively, aqueous humor samples and the affected corneal tissue were collected for subsequent culture and identification of bacteria and fungi. Voriconazole injection was used throughout the procedure for corneal margin and anterior chamber irrigation. The donor cornea, sourced from our eye bank, and residual donor cornea, along with corneal preservation solution (Corneal Chamber, Alchimial, Italy), were sent for bacterial and fungal culture postoperatively. The postoperative regimen consisted of local administration of natamycin and tacrolimus eye drops (0.1%, Senju Pharmaceutical Co, Japan), as well as levofloxacin eye drops (0.5%, Senju Pharmaceutical Co, Japan). Additionally, itraconazole capsules (200 mg daily, Xi'an Yangsen Pharmaceutical Co., Ltd., China) were orally administered.

A The clinical presentation is characterized by peripheral central corneal opacity and infiltration, which exhibit typical elevated lesions, a dry surface, and feathery infiltrating margins. B . Confocal microscopy reveals the presence of fungal hyphae. C . Fungal hyphae are observed in corneal scrapings with Gram staining. D . Corneal scrapings with potassium hydroxide (KOH) wet mount demonstrate the presence of fungal hyphae

A After treatment, the corneal ulcer has healed, with localized margins and corneal perforation. B No fungal hyphae are observed in corneal scrapings with Gram staining, but inflammatory cells are present

Following corneal transplantation, the graft remained transparent. However, the aqueous humor exhibited gradual turbidity, and by the fourth postoperative day, anterior chamber pus accumulation was observed, prompting concern regarding a potential recurrence of fungal infection. Consequently, the anterior chamber was aspirated to remove the pus, and a voriconazole injection was administered for anterior chamber irrigation and medication. Intraoperatively, it was noted that the anterior chamber pus was thin and watery in consistency, in contrast to the thicker purulent fluid observed in fungal infections. An examination of the anterior chamber pus revealed the absence of fungal hyphae (Fig. 3 D). Postoperatively, there was no significant improvement in the anterior chamber reaction, and the cornea exhibited mild edema.

A Following corneal transplantation, there was an accumulation of pus in the anterior chamber of the eye, exhibiting a thin and watery consistency. B Subsequent to treatment, there was a discernible reduction in anterior chamber pus. C The corneal graft appeared grayish-white and opaque, and the anterior chamber pus completely disappeared. D Gram staining of corneal scrapings did not reveal any fungal hyphae, but did indicate the presence of a considerable number of inflammatory cells. E Turbidity was observed in the vitreous cavity, resembling sediment. F The vitreous opacities exhibited a noticeable reduction in comparison to the pre-treatment state

A microbiological examination of the recipient corneal ulcer, aqueous humour, donor cornea, and preservation solution yielded negative results for bacteria and fungi, which is thought to be the consequence of preoperative antifungal and antibacterial treatment. However, given the possibility of other infections occurring postoperatively, aqueous humour and anterior chamber pus from the operated eye were collected for metagenomic next-generation sequencing (mNGS) test. Total genomic DNA was extracted using a nucleic acid extraction kit, then fragmented to 200 bp and used to build a library with end-repaired, adapter-ligation, and polymerase chain reaction amplification. The prepared library was sequenced on the MGISEQ-2000 sequencing platform (MGI, China). The reads were finally aligned to the Microbial Genome Databases, which contain the whole-genome sequences of 8,472 viruses, 10,537 bacteria, 903 fungi and 288 parasites. During the aforementioned interval, the previously administered eye drops were maintained. This was accompanied by an increase in the rate of anterior chamber pus leakage, culminating in the clouding of the corneal graft (Figure 3 A). The mNGS results identified O. anthropi, with 321 sequences with a relative abundance of 98.98%. Additionally, a vitreous opacity was revealed through a B-ultrasound examination. (Fig. 3 E). To treat O. anthropic, ceftazidime (25 mg/ml), an amikacin (4 mg/ml), and vancomycin (10 mg/ml) were administered to the anterior chamber and vitreous, respectively, three times each. The oral antifungal medication was discontinued, and a cefuroxime injection (1.0 g, administered three times a day) was administered intracamerally. To prevent a recurrence of fungal infection, natamycin eye drops were administered four times daily, in conjunction with tobramycin eye drops (0.3%, Tobramycin Eye Drops, Alcon-Couvreur n. v, Belgium), and levofloxacin eye drops (0.5%, Senju Pharmaceutical Co, Japan) at 1-hour intervals. Following three days of treatment, there was a reduction in anterior chamber pus (see Fig. 3 B). After a further ten days of treatment, the anterior chamber pus had been absorbed completely. However, the corneal graft remained cloudy (Fig. 3 C), with ultrasound indicating that the vitreous opacities had reduced (Fig. 3 F). The patient's condition remained stable, with effective infection control being maintained.

Six months following corneal transplantation, the operated eye exhibited corneal opacities and pseudo-pterygium (Fig. 4 A). B-ultrasound examination did not reveal any abnormalities. To enhance visual function, a secondary partial penetrating keratoplasty was conducted concurrently with a cataract removal procedure. Postoperatively, Tobramycin eye drops were administered for the purpose of prophylaxis against infection, in conjunction with Tacrolimus and Prednisolone Acetate Ophthalmic Suspension (1%, Allergan Pharmaceuticals Ireland) for the prevention of rejection. One month following the procedure, the corneal graft was observed to be transparent, with a corrected visual acuity of 0.1 (Fig. 4 B).

A Pseudo-pterygium and corneal opacities developed six months after corneal transplantation. B After the second corneal transplantation, the corneal graft became transparent

Fungal keratitis stands out as the predominant cause of blindness in patients with infectious corneal diseases in China [ 10 ]. Therapeutic keratoplasty serves as a pivotal intervention in the management of progressive fungal keratitis when conventional pharmaceutical therapies prove ineffective. However, a considerable contributor to the failure of corneal transplantation is the recurrence of postoperative fungal infections [ 11 ]. Risk factors for infection recurrence encompass the size of corneal ulcer infiltration, graft dimensions, and the type of fungus involved [ 12 ]. Furthermore, comprehensive antifungal treatment prior to corneal transplantation constitutes a critical determinant for surgical success. In the presented case, the patient received standardized antifungal treatment post-diagnosis, resulting in favorable therapeutic outcomes. Undertaking corneal transplantation at this juncture successfully averted postoperative recurrence of fungal infections. Hence, judiciously selecting the timing for corneal transplantation emerges as a pivotal strategy in controlling the recurrence of fungal corneal ulcers.

Anterior chamber pus was observed on the fourth day after the surgery. Given past experience, a recurrence of fungal infection was suspected and voriconazole anterior chamber lavage was performed on the operative eye. However, the observed pus appeared thin and lacked the characteristic viscosity typically seen in fungal infections [ 13 ]. Subsequent exacerbation of the patient's condition after antifungal treatment led to concerns regarding potential infection by other pathogens. In order to rule out the possibility of contamination from the donor cornea, another patient that had received a corneal transplant from the same donor at the same time was continuously monitored. No signs of infection were found.

Due to the fact that microbial cultures and smear examinations of the affected cornea failed to detect any pathogens, we conducted next-generation sequencing (NGS) on the anterior chamber pus to identify the infectious agent. Metagenomic is a diagnostic technique widely used in microbiological research but infrequently employed in routine clinical microbiological diagnostics. It offers a rapid and accurate advantage in determining the nature and type of infection in clinical diagnosis [ 14 ], NGS and shotgun sequencing particularly demonstrating excellent diagnostic value for infections on the ocular surface and within the eye [ 15 ,  16 ]. In the event that the traditional microbiological tests employed in ophthalmology prove to be ineffective, it can serve as a highly effective supplementary diagnostic tool, markedly enhancing the detection rate of microorganisms that are particularly challenging to cultivate in clinical samples [ 17 ].

O. anthropi is widely present in the environment, soil, and water sources (physiological saline, preservative solutions, dialysis fluid) [ 5 , 18 ]. Additionally, it has been isolated from human bodily fluids [ 19 ]. As a rare conditional pathogen, most reported cases involve hospital-acquired infections, with infected patients using various indwelling and invasive medical devices such as central venous catheters, artificial heart valves, and drainage tubes [ 6 , 20 , 21 ]. Existing clinical case reports have found that O. anthropi-induced endophthalmitis is more common after cataract intraocular lens implantation [ 8 , 9 , 22 , 23 ], and there is also a reported case of infection after artificial corneal implantation [ 24 ]. Infections related to implants may be associated with the propensity of O. anthropi to adhere to the surfaces of synthetic materials [ 25 ]. Some studies also suggest a correlation between post-cataract surgery endophthalmitis and contamination of intraocular irrigation fluids [ 22 ]. Another report found that after thorough cleaning of the cannula kit of an ultrasonic emulsification machine, the hospital's outbreak of O. anthropi infection promptly disappeared [ 26 ]. This report further confirms this hypothesis.

O. anthropi, being an opportunistic pathogen, manifests infection significantly in individuals with compromised immune function and a history of both local and systemic antibiotic usage [ 8 ] [ 27 , 28 ]. However, in this particular case, the patient did not employ any indwelling or invasive medical devices, and comprehensive examinations, both physical and systemic, failed to reveal any symptoms. Based on the patient's medical history, the human Ochrobactrum anthropi infection in this case can be attributed to local immune function decline after corneal transplantation. In addition, the patient had a history of topical antibiotic use for 1 month prior to surgery, which increased the risk of human O. anthropi infection due to dysbiosis and antibiotic resistance.

Despite the generally perceived low virulence of O.anthropi, its infection rates have gradually increased in recent years due to its inherent multidrug resistance to antibiotics. O. anthropi exhibits resistance to β-lactam drugs, particularly cephalosporins and penicillins, while being sensitive to quinolone drugs and aminoglycoside drugs, especially amikacin and gentamicin [ 29 , 30 ]. Our patient received prompt and adequate antibiotic treatment upon confirmation of the infection, effectively controlling the infection rapidly. However, it is noteworthy that, after 14 days of treatment, although the infection was well controlled, the corneal graft still exhibited cloudiness. Currently, while there have been numerous reports on endophthalmitis caused by O. anthropi, there is limited documentation on the toxicity of this bacterium to the cornea itself and the resulting pathological changes. Nandini et al. reported a case of corneal inflammation caused by O. anthropi infection, presenting as anterior chamber purulence in a patient with a history of viral keratitis. This case was ultimately diagnosed as O. anthropi infection, with corneal histopathological findings showing detachment of the posterior elastic layer [ 31 ]. Generally, bacterial infections can lead to pathological changes such as corneal opacification, edema, ulcer formation, and endothelial damage [ 32 ]. Nevertheless, in the case of corneal tissue infection by O. anthropi, which is generally regarded as a Gram-negative bacterium of low virulence, the potential exists for the pathogen to elicit more severe pathological alterations. The cloudiness of the corneal graft subsequent to O. anthropi infection in this instance may be attributed to the local eye drops and anterior chamber injections employed during the infection treatment, which may have resulted in corneal endothelial damage [ 33 , 34 , 35 ].

The case presented constitutes the initial report of O. anthropi-induced keratitis following corneal transplantation. The clinical manifestations of the infection are lacking in specificity. Therefore, ophthalmologists must select the most appropriate diagnostic approach to identify the pathogen and guide therapeutic interventions. For patients with conditions predisposing to local immune dysfunction, the possibility of O. anthropi infection should be considered promptly upon the onset of infection. The corneal pathology induced by this pathogen warrants attention and merits further investigation.

Availability of data and materials

No datasets were generated or analysed during the current study.

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Liu, L., Wang, C., Xu, H. et al. Ochrobactrum anthropi infection following corneal transplantation -a case report and review of literature. BMC Ophthalmol 24 , 234 (2024). https://doi.org/10.1186/s12886-024-03472-z

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The four building blocks of change

Large-scale organizational change has always been difficult, and there’s no shortage of research showing that a majority of transformations continue to fail. Today’s dynamic environment adds an extra level of urgency and complexity. Companies must increasingly react to sudden shifts in the marketplace, to other external shocks, and to the imperatives of new business models. The stakes are higher than ever.

So what’s to be done? In both research and practice, we find that transformations stand the best chance of success when they focus on four key actions to change mind-sets and behavior: fostering understanding and conviction, reinforcing changes through formal mechanisms, developing talent and skills, and role modeling. Collectively labeled the “influence model,” these ideas were introduced more than a dozen years ago in a McKinsey Quarterly article, “ The psychology of change management .” They were based on academic research and practical experience—what we saw worked and what didn’t.

Digital technologies and the changing nature of the workforce have created new opportunities and challenges for the influence model (for more on the relationship between those trends and the model, see this article’s companion, “ Winning hearts and minds in the 21st century ”). But it still works overall, a decade and a half later (exhibit). In a recent McKinsey Global Survey, we examined successful transformations and found that they were nearly eight times more likely to use all four actions as opposed to just one. 1 1. See “ The science of organizational transformations ,” September 2015. Building both on classic and new academic research, the present article supplies a primer on the model and its four building blocks: what they are, how they work, and why they matter.

Fostering understanding and conviction

We know from research that human beings strive for congruence between their beliefs and their actions and experience dissonance when these are misaligned. Believing in the “why” behind a change can therefore inspire people to change their behavior. In practice, however, we find that many transformation leaders falsely assume that the “why” is clear to the broader organization and consequently fail to spend enough time communicating the rationale behind change efforts.

This common pitfall is predictable. Research shows that people frequently overestimate the extent to which others share their own attitudes, beliefs, and opinions—a tendency known as the false-consensus effect. Studies also highlight another contributing phenomenon, the “curse of knowledge”: people find it difficult to imagine that others don’t know something that they themselves do know. To illustrate this tendency, a Stanford study asked participants to tap out the rhythms of well-known songs and predict the likelihood that others would guess what they were. The tappers predicted that the listeners would identify half of the songs correctly; in reality, they did so less than 5 percent of the time. 2 2. Chip Heath and Dan Heath, “The curse of knowledge,” Harvard Business Review , December 2006, Volume 8, Number 6, hbr.org.

Therefore, in times of transformation, we recommend that leaders develop a change story that helps all stakeholders understand where the company is headed, why it is changing, and why this change is important. Building in a feedback loop to sense how the story is being received is also useful. These change stories not only help get out the message but also, recent research finds, serve as an effective influencing tool. Stories are particularly effective in selling brands. 3 3. Harrison Monarth, “The irresistible power of storytelling as a strategic business tool,” Harvard Business Review , March 11, 2014, hbr.org.

Even 15 years ago, at the time of the original article, digital advances were starting to make employees feel involved in transformations, allowing them to participate in shaping the direction of their companies. In 2006, for example, IBM used its intranet to conduct two 72-hour “jam sessions” to engage employees, clients, and other stakeholders in an online debate about business opportunities. No fewer than 150,000 visitors attended from 104 countries and 67 different companies, and there were 46,000 posts. 4 4. Icons of Progress , “A global innovation jam,” ibm.com. As we explain in “Winning hearts and minds in the 21st century,” social and mobile technologies have since created a wide range of new opportunities to build the commitment of employees to change.

Reinforcing with formal mechanisms

Psychologists have long known that behavior often stems from direct association and reinforcement. Back in the 1920s, Ivan Pavlov’s classical conditioning research showed how the repeated association between two stimuli—the sound of a bell and the delivery of food—eventually led dogs to salivate upon hearing the bell alone. Researchers later extended this work on conditioning to humans, demonstrating how children could learn to fear a rat when it was associated with a loud noise. 5 5. John B. Watson and Rosalie Rayner, “Conditioned emotional reactions,” Journal of Experimental Psychology , 1920, Volume 3, Number 1, pp. 1–14. Of course, this conditioning isn’t limited to negative associations or to animals. The perfume industry recognizes how the mere scent of someone you love can induce feelings of love and longing.

Reinforcement can also be conscious, shaped by the expected rewards and punishments associated with specific forms of behavior. B. F. Skinner’s work on operant conditioning showed how pairing positive reinforcements such as food with desired behavior could be used, for example, to teach pigeons to play Ping-Pong. This concept, which isn’t hard to grasp, is deeply embedded in organizations. Many people who have had commissions-based sales jobs will understand the point—being paid more for working harder can sometimes be a strong incentive.

Despite the importance of reinforcement, organizations often fail to use it correctly. In a seminal paper “On the folly of rewarding A, while hoping for B,” management scholar Steven Kerr described numerous examples of organizational-reward systems that are misaligned with the desired behavior, which is therefore neglected. 6 6. Steven Kerr, “On the folly of rewarding A, while hoping for B,” Academy of Management Journal , 1975, Volume 18, Number 4, pp. 769–83. Some of the paper’s examples—such as the way university professors are rewarded for their research publications, while society expects them to be good teachers—are still relevant today. We ourselves have witnessed this phenomenon in a global refining organization facing market pressure. By squeezing maintenance expenditures and rewarding employees who cut them, the company in effect treated that part of the budget as a “super KPI.” Yet at the same time, its stated objective was reliable maintenance.

Even when organizations use money as a reinforcement correctly, they often delude themselves into thinking that it alone will suffice. Research examining the relationship between money and experienced happiness—moods and general well-being—suggests a law of diminishing returns. The relationship may disappear altogether after around $75,000, a much lower ceiling than most executives assume. 7 7. Belinda Luscombe, “Do we need $75,000 a year to be happy?” Time , September 6, 2010, time.com.

Would you like to learn more about our People & Organizational Performance Practice ?

Money isn’t the only motivator, of course. Victor Vroom’s classic research on expectancy theory explained how the tendency to behave in certain ways depends on the expectation that the effort will result in the desired kind of performance, that this performance will be rewarded, and that the reward will be desirable. 8 8. Victor Vroom, Work and motivation , New York: John Wiley, 1964. When a Middle Eastern telecommunications company recently examined performance drivers, it found that collaboration and purpose were more important than compensation (see “Ahead of the curve: The future of performance management,” forthcoming on McKinsey.com). The company therefore moved from awarding minor individual bonuses for performance to celebrating how specific teams made a real difference in the lives of their customers. This move increased motivation while also saving the organization millions.

How these reinforcements are delivered also matters. It has long been clear that predictability makes them less effective; intermittent reinforcement provides a more powerful hook, as slot-machine operators have learned to their advantage. Further, people react negatively if they feel that reinforcements aren’t distributed fairly. Research on equity theory describes how employees compare their job inputs and outcomes with reference-comparison targets, such as coworkers who have been promoted ahead of them or their own experiences at past jobs. 9 9. J. S. Adams, “Inequity in social exchanges,” Advances in Experimental Social Psychology , 1965, Volume 2, pp. 267–300. We therefore recommend that organizations neutralize compensation as a source of anxiety and instead focus on what really drives performance—such as collaboration and purpose, in the case of the Middle Eastern telecom company previously mentioned.

Developing talent and skills

Thankfully, you can teach an old dog new tricks. Human brains are not fixed; neuroscience research shows that they remain plastic well into adulthood. Illustrating this concept, scientific investigation has found that the brains of London taxi drivers, who spend years memorizing thousands of streets and local attractions, showed unique gray-matter volume differences in the hippocampus compared with the brains of other people. Research linked these differences to the taxi drivers’ extraordinary special knowledge. 10 10. Eleanor Maguire, Katherine Woollett, and Hugo Spires, “London taxi drivers and bus drivers: A structural MRI and neuropsychological analysis,” Hippocampus , 2006, Volume 16, pp. 1091–1101.

Despite an amazing ability to learn new things, human beings all too often lack insight into what they need to know but don’t. Biases, for example, can lead people to overlook their limitations and be overconfident of their abilities. Highlighting this point, studies have found that over 90 percent of US drivers rate themselves above average, nearly 70 percent of professors consider themselves in the top 25 percent for teaching ability, and 84 percent of Frenchmen believe they are above-average lovers. 11 11. The art of thinking clearly, “The overconfidence effect: Why you systematically overestimate your knowledge and abilities,” blog entry by Rolf Dobelli, June 11, 2013, psychologytoday.com. This self-serving bias can lead to blind spots, making people too confident about some of their abilities and unaware of what they need to learn. In the workplace, the “mum effect”—a proclivity to keep quiet about unpleasant, unfavorable messages—often compounds these self-serving tendencies. 12 12. Eliezer Yariv, “‘Mum effect’: Principals’ reluctance to submit negative feedback,” Journal of Managerial Psychology , 2006, Volume 21, Number 6, pp. 533–46.

Even when people overcome such biases and actually want to improve, they can handicap themselves by doubting their ability to change. Classic psychological research by Martin Seligman and his colleagues explained how animals and people can fall into a state of learned helplessness—passive acceptance and resignation that develops as a result of repeated exposure to negative events perceived as unavoidable. The researchers found that dogs exposed to unavoidable shocks gave up trying to escape and, when later given an opportunity to do so, stayed put and accepted the shocks as inevitable. 13 13. Martin Seligman and Steven Maier, “Failure to escape traumatic shock,” Journal of Experimental Psychology , 1967, Volume 74, Number 1, pp. 1–9. Like animals, people who believe that developing new skills won’t change a situation are more likely to be passive. You see this all around the economy—from employees who stop offering new ideas after earlier ones have been challenged to unemployed job seekers who give up looking for work after multiple rejections.

Instilling a sense of control and competence can promote an active effort to improve. As expectancy theory holds, people are more motivated to achieve their goals when they believe that greater individual effort will increase performance. 14 14. Victor Vroom, Work and motivation , New York: John Wiley, 1964. Fortunately, new technologies now give organizations more creative opportunities than ever to showcase examples of how that can actually happen.

Role modeling

Research tells us that role modeling occurs both unconsciously and consciously. Unconsciously, people often find themselves mimicking the emotions, behavior, speech patterns, expressions, and moods of others without even realizing that they are doing so. They also consciously align their own thinking and behavior with those of other people—to learn, to determine what’s right, and sometimes just to fit in.

While role modeling is commonly associated with high-power leaders such as Abraham Lincoln and Bill Gates, it isn’t limited to people in formal positions of authority. Smart organizations seeking to win their employees’ support for major transformation efforts recognize that key opinion leaders may exert more influence than CEOs. Nor is role modeling limited to individuals. Everyone has the power to model roles, and groups of people may exert the most powerful influence of all. Robert Cialdini, a well-respected professor of psychology and marketing, examined the power of “social proof”—a mental shortcut people use to judge what is correct by determining what others think is correct. No wonder TV shows have been using canned laughter for decades; believing that other people find a show funny makes us more likely to find it funny too.

Today’s increasingly connected digital world provides more opportunities than ever to share information about how others think and behave. Ever found yourself swayed by the number of positive reviews on Yelp? Or perceiving a Twitter user with a million followers as more reputable than one with only a dozen? You’re not imagining this. Users can now “buy followers” to help those users or their brands seem popular or even start trending.

The endurance of the influence model shouldn’t be surprising: powerful forces of human nature underlie it. More surprising, perhaps, is how often leaders still embark on large-scale change efforts without seriously focusing on building conviction or reinforcing it through formal mechanisms, the development of skills, and role modeling. While these priorities sound like common sense, it’s easy to miss one or more of them amid the maelstrom of activity that often accompanies significant changes in organizational direction. Leaders should address these building blocks systematically because, as research and experience demonstrate, all four together make a bigger impact.

Tessa Basford is a consultant in McKinsey’s Washington, DC, office; Bill Schaninger is a director in the Philadelphia office.

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