That isn't what that paper says. From "limitations of the evidence": >All 5 studies were assessed as being at high risk of bias What is not here is any study

That isn't what that paper says. From "limitations of the evidence": >All 5 studies were assessed as being at high risk of bias What is not here is any study controlling for the factors you mention and finding a zero correlation as you claim. The conclusion, which I assume you are referring to, states: >There is no evidence to support taking vitamin D supplements to specifically prevent or treat COVID-19. However, all people should continue to follow UK Government advice on daily vitamin D supplementation to maintain bone and muscle health during the COVID-19 pandemic. Since vitamin D supplements are already advised for the general population, it is extremely unlikely they would be recommended for specifically COVID-19 without very high-quality evidence. Unless dosing recommendations can be given with good reason to believe those recommendations would be beneficial, the only effect that could come of a positive conclusion is risk compensation, i.e. increased risky behaviors, which is bad.