A study published in PLOS Medicine by Guillaume Butler-Laporte and Tomoko Nakanishi at McGill University in Quebec, Canada suggests that increased Vitamin D levels may protect against Covid-19. The study, however, remains inconclusive and is possibly subject to confounding. Vitamin D's ability to protect against severe Covid-19 illness has long been discussed by public health experts. Unfortunately, it lacks supporting evidence.
Researchers conducted a Mendelian randomization study using genetic variants strongly associated with increased Vitamin D levels to assess its relationship with Covid-19 susceptibility.
The scientists analyzed genetic variants of 4,134 individuals with Covid-19 and 1,284,876 without Covid-19, from 11 countries to determine whether genetic predisposition for higher Vitamin D levels was associated with less-severe disease outcomes in people with Covid-19.
The results showed no evidence for an association between genetically predicted vitamin D levels and Covid-19 susceptibility, hospitalization, or severe disease, suggesting that raising circulating vitamin D levels through supplementation may not improve Covid-19 outcomes in the general population. The study however, had its important limitations, including that the research did not include individuals with Vitamin D deficiency, and it remains possible that truly deficient patients may benefit from supplementation for Covid-19 related protection and outcomes.
The authors said, “Vitamin D supplementation as a public health measure to improve outcomes is not supported by this study. Most importantly, our results suggest that investment in other therapeutic or preventative avenues should be prioritized for Covid-19 randomized clinical trials.”
According to Dr Butler-Laporte, most vitamin D studies are very difficult to interpret since they cannot adjust for the known risk factors for severe Covid-19 (e.g. older age, institutionalization, having chronic diseases) which are also predictors of low vitamin D.