Comment by alicorn

I am lazy and did not read the study, sorry. But nowhere in the comments I see discussion related to whether it somehow accounts for dietary variance in vitamin D intake via fortified products. In Sweden, for example, because we are so far north, milk is routinely fortified with vitamin D. So even if a person has a genetic variance for low vitamin D, they will still be supplemented without actively doing anything, as long as they drink milk. On the other hand it stands to reason that if foodstuff fortification had a significant effect on vitD levels in population AND vitD had significant effect on immunity / severity of covid-19 then Sweden would have statistically significantly lower covid-19 infection and mortality rates than countries where food fortification with vitD is not practiced. Afaik that is not the case, otoh there is an insane amount of confounding variables so it might not be possible to assess such an effect in any scientifically valid manner.