Can vitamin D3 supplementation reduce COVID-19 severity?

In a recent study published in the Nutrients, a group of researchers assessed the effectiveness of Vitamin D3 supplementation in reducing intensive care unit (ICU) admissions and coronavirus disease 2019 (COVID-19)-related mortality through a meta-analysis of 13 randomized clinical trials.

Study: Effect of Vitamin D3 Supplementation on Severe COVID-19: A Meta-Analysis of Randomized Clinical Trials. Image Credit: Oldesign/Shutterstock.comStudy: Effect of Vitamin D3 Supplementation on Severe COVID-19: A Meta-Analysis of Randomized Clinical Trials. Image Credit: Oldesign/


At the end of 2019, COVID-19, caused by the highly contagious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, quickly escalated into a global pandemic, impacting healthcare systems worldwide. By February 2024, over 7 million deaths had been reported.

COVID-19 can cause severe respiratory issues, including acute respiratory distress syndrome (ARDS), particularly in older patients with comorbidities like cardiovascular disease. Vitamin D, known for its immunomodulatory effects, has been suggested to reduce severe COVID-19 outcomes by regulating immune responses and reducing inflammation.

Further research is needed to establish the efficacy of Vitamin D3 supplementation in improving clinical outcomes for COVID-19 patients across diverse populations and variants.

About the study 

The present analysis adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Literature searches were conducted in PubMed, Embase, Web of Science, and the Cochrane Central Register of Controlled Trials as of 15 February 2024 using keywords related to Vitamin D and COVID-19, focusing on severe cases.

The inclusion criteria were restricted to control-compared randomized clinical trials (RCTs) that examined the impact of vitamin D3 supplementation on patients with severe COVID-19. Studies not in English or lacking relevant endpoints like hospitalization length, ICU admissions, or mortality rates were excluded.

For data extraction, continuous data presented as medians or percentages were converted into means or whole numbers using established statistical methods to ensure uniformity across studies.

The quality of the studies was rigorously assessed using the Cochrane Collaboration’s tool, which evaluates aspects like randomization, blinding, and bias, categorizing them into low, high, or unclear risk.

Statistical analysis was performed using R, calculating relative risks and mean differences with 95% confidence intervals to determine the effects of vitamin D3 supplementation. The heterogeneity of results was assessed with I2 statistics, interpreting various levels of heterogeneity and its impact on the meta-analysis.

Potential publication bias was evaluated through funnel plots and regression tests, ensuring the robustness of the findings. The significance level was set at p < 0.05, emphasizing the precision of the statistical evaluation.

Study results 

The search for relevant literature on the impact of Vitamin D3 supplementation on COVID-19 outcomes initially yielded 1,222 articles, which were narrowed down after removing duplicates and irrelevant studies such as meta-analyses, systematic reviews, and non-human studies.

The selection was further refined to include only RCTs written in English that focused on severe COVID-19 cases, resulting in 13 articles that qualified for in-depth analysis.

These studies varied in their control group setups: five included a placebo, four had no supplementation, and four used a standard dose of Vitamin D3. The studies included diverse demographics and were conducted across several countries, including Spain, Brazil, Switzerland, Mexico, Egypt, Russia, France, Argentina, Belgium, Iran, and Croatia.

The risk of bias in these studies was thoroughly assessed, and four were found to have a high risk of bias, while the others showed relatively low risk. This risk assessment was crucial for ensuring the reliability of the meta-analysis results.

The analysis of the effect of Vitamin D3 supplementation revealed mixed results. While there was no significant difference in the length of hospitalization for COVID-19 patients between the supplementation and control groups, the supplementation did show a 27% reduction in ICU admissions. However, it did not significantly affect the length of ICU stays.

Regarding respiratory support, Vitamin D3 supplementation did not significantly alter the number of cases requiring supplemental oxygenation or the duration of such oxygenation.

In terms of mortality, the supplementation did not significantly affect overall mortality rates. Still, it was associated with a 44% reduction in deaths related to COVID-19, suggesting a potential benefit in the most severe cases.

Finally, the publication bias analysis using funnel plots and regression tests generally indicated an absence of bias across most outcomes. However, there was a notable exception for the number of ICU admissions, where publication bias was detected. 


To summarize, the meta-analysis of 13 randomized clinical trials found that Vitamin D3 potentially reduces ICU admissions and COVID-19-related mortality but does not significantly impact hospitalization length, ICU stay, supplemental oxygen requirements, or overall mortality.

These results align with some studies highlighting Vitamin D’s benefits against severe COVID-19, though others report no substantial effects. The analysis revealed publication bias, suggesting the underrepresentation of smaller studies with negative outcomes. 

Journal reference:
Vijay Kumar Malesu

Written by

Vijay Kumar Malesu

Vijay holds a Ph.D. in Biotechnology and possesses a deep passion for microbiology. His academic journey has allowed him to delve deeper into understanding the intricate world of microorganisms. Through his research and studies, he has gained expertise in various aspects of microbiology, which includes microbial genetics, microbial physiology, and microbial ecology. Vijay has six years of scientific research experience at renowned research institutes such as the Indian Council for Agricultural Research and KIIT University. He has worked on diverse projects in microbiology, biopolymers, and drug delivery. His contributions to these areas have provided him with a comprehensive understanding of the subject matter and the ability to tackle complex research challenges.    


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  1. Doug Foley Doug Foley Canada says:

    Very disappointing not knowing the dose of D-3 supplementation given, especially in light of the RDA being only 10% of what is required, ie, according to recent findings, D-3 RDA recommendations were based on flawed methodology and incorrect mathematics.

  2. Will MacPheat Will MacPheat United States says:

    It does not mention the amount of vitamin D3 given to the patients and of course it excludes previous studies that aren't in English which is very convenient. In 2021 there was a German study that looked at death rates for people with covid and it looked at there blood levels of vitamin d. It specifically looked at people who had known levels of vitamin d prior to getting covid to exclude the possibility that covid somehow affected their blood levels. And what the data showed was that at 50 nanograms per milliliter you reach 0 deaths. Of course the study didn't say that there would be no deaths because there's always going to be some unusual case where somebody dies but they also went on to say that you needed to take 5,000 IU's per day of vitamin D3 to reach that level of 50 nanograms per milliliter. Nobody seems to want to report this information.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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