Vitamin D uncorrelated with Covid severity in those of European descent
Note that this study was not a placebo controlled trial, and it was not even based on data about actual vitamin D levels. Instead, it was retrospective analysis using instrumental variables. I'm not saying its conclusions are wrong, I'm just saying that IMHO it's not a definitive study.Quoting the study:"Although we will need well-powered and carefully executed randomised trials and a subsequent meta-analysis of the different studies to provide an accurate estimate of the effect of vitamin D on COVID-19 prevention and severity, we can anticipate the results of such studies by comparing individuals who are genetically predisposed to lower vitamin D levels with those who are not, based on the Mendelian randomisation (MR) paradigm. In a randomised controlled trial, we would minimise the effect of confounding factors by randomly assigning participants to a treatment group receiving vitamin D supplements or to a control group receiving a placebo and thus estimate the true effect of the intervention. In the natural experiment of MR, genetic variants predisposing the individual to higher levels of vitamin D are assigned randomly at conception, based on the genetic polymorphisms of their parents, in relation to other possible confounding traits. As genetic polymorphisms remain constant throughout life and the individual does not change their vitamin D intake according to their genotype, the use of this information can provide indirect evidence of causality.18 Here, using data from genome-wide association (GWA) studies for vitamin D levels, vitamin D deficiency and COVID-19 incidence and severity, we test whether genetically increased vitamin D levels are associated with SARS-CoV-2 infection risk and COVID-19 severity."