While previous research early in the pandemic suggested that vitamin D cuts the risk of contracting Covid-19, a new study finds there is no genetic evidence that it works as a protective measure against the coronavirus. According to the researchers, including Guillaume Butler-Laporte from McGill University, vitamin D supplementation as a public health measure to improve outcomes is not supported by this study. Most importantly, the results suggest that investment in other therapeutic or preventative avenues should be prioritised for Covid-19 randomised clinical trials. "Most vitamin D studies are very difficult to interpret since they cannot adjust for the known risk factors for severe Covid-19 such as older age or having chronic diseases, which are also predictors of low vitamin D," said Butler-Laporte. For the study, published in the journal PLOS Medicine, the researchers conducted a Mendelian randomisation study using genetic variants strongly associated with increased vitamin D levels. They looked at genetic variants of 14,134 individuals with Covid-19 and over 1.2 million individuals without the disease from 11 countries. The researchers found that among people who did develop the disease, there was no difference between vitamin D levels and a likelihood of being hospitalized or falling severely ill.