Genetic evidence does not support vitamin D as a protective measure against Covid-19, say researchers.

The team from McGill University in Quebec, Canada, 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 were associated with less-severe disease outcomes in people with Covid-19.

The results, published in PLOS Medicine, showed no evidence for an association between genetically predicted vitamin D levels and Covid-19 susceptibility, hospitalisation, or severe disease. This suggests that raising circulating vitamin D levels through supplementation may not improve Covid-19 outcomes in the general population.

Increased vitamin D levels, as reflected by 25-hydroxy vitamin D measurements, have been proposed to protect against Covid-19 based on in vitro, observational, and ecological studies.

But, "Vitamin D supplementation as a public health measure to improve outcomes is not supported by this study," said researchers including Guillaume Butler-Laporte and Tomoko Nakanishi from the varsity.

However, the team noted several 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.

Additionally, the genetic variants were obtained only from individuals of European ancestry, so future studies will be needed to determine the relationship with Covid-19 outcomes in other populations.

A previous study also showed similar results. Scientists from the University of Sao Paulo conducted a clinical trial in Brazil with 240 patients who were given 200,000 IU of vitamin D3 on admission to hospital.

The supplementation did not reduce length of stay or affect the proportion requiring intensive care, according to the study published in the Journal of the American Medical Association (JAMA).