Association Between Vitamin D and COVID-19-Related Outcomes: An Umbrella Review of Meta-Analyses.
Level 1 - systematic review of randomized trials
Systematic umbrella review synthesizing multiple meta-analyses
PubMed 39907316 · doi:10.1093/nutrit/nuae225
What was done
An umbrella review searched PubMed, Embase, Web of Science, Scopus, and the Cochrane Database of Systematic Reviews from January 1, 2020, to June 15, 2024. Two reviewers independently extracted data and evaluated study quality to synthesize meta-analytic evidence regarding vitamin D status, supplementation, and COVID-19 clinical outcomes.
What was found
Low vitamin D levels were associated with an increased risk of infection by 1.26- to 2.18-fold, severe illness by 1.50- to 5.57-fold, ICU admission by over 2-fold, and death by 1.22- to 4.15-fold, with an average increase in hospital length of stay of 0.54 days. Significant mean differences (MD) in vitamin D levels were reported between COVID-19-positive and negative individuals (MD = -3.22 ng/mL; 95% CI, -5.18 to -1.25), severe and mild cases (MD = -4.60 ng/mL; 95% CI, -5.49 to -3.71), and nonsurvivors and survivors (MD = -6.59 ng/mL; 95% CI, -8.94 to -4.24). Vitamin D supplementation had a nonsignificant effect on infection and mortality rates, though it was associated with reduced severity (ICU admission, mechanical ventilation) and shorter hospital stays.
Why it matters
This review distinguishes between observational correlations of vitamin D deficiency and interventional trial findings, highlighting that while low serum vitamin D consistently tracks with worse disease, evidence that supplementation reduces mortality or prevents infection remains unproven.
Limits
The abstract explicitly notes that the methodological quality of most included meta-analyses and the level of evidence for most outcomes are very low. The total number of included meta-analyses and individual participants is not reported in the abstract. Observational associations remain prone to residual confounding and reverse causation.
Cited by
- supports Research during the COVID-19 pandemic demonstrated that people who were vitamin D deficient had higher mortality from COVID-19.