Vitamin D, part 1: back to basics
The author explains the following, regarding Vitamin D studies:> Most studies follow this pattern: Two sets of people are evaluated. One set has a certain disease (diabetes, for example). The other set does not have the disease. Vitamin D levels are measured in both groups. Vitamin D deficiency is found to be much more common in the group of diseased individuals.If this is true, I wonder if most studies aren’t falling short for failing to control for Vitamin D deficiency.  Couldn’t the studies be structured differently?Let’s say we want to know the effects of Vitamin D on Covid.  What if, instead of measuring Vitamin D deficiency in a group with the malady and a group without (analogous to what the author suggests most studies do):We had two groups made up of Vitamin D deficient people.  We gave the first group a Vitamin D supplement and the other a placebo. We then observed both groups out in the wild (ideally a place with a high R), measuring for infections.  If the supplement folks were infected at significantly lower rates than placebo folks, wouldn’t this be better at demonstrating causation?