[nextos]

There are serious clinical trials with randomization and placebo that have repeatedly shown vitamin D supplementation reduces autoimmune disease rate. For example [1].

Obviously, the effect of a compound that does not require prescription and has few side effects is modest. But we are talking about a two digit % reduction in incidence, which is pretty respectable. At individual level, it is of course hard to see any effect. And if you are in trouble already, you will typically need, something stronger, a drug.

[1] https://www.bmj.com/content/376/bmj-2021-066452.full

[Aurornis]

That's one of the weaker study outcomes I've seen. The Vitamin D arm just baaarely reached their definition of being significant. If the numbers had differed by only a single patient they would have had to call it "not significant"

Whenever studies test multiple things in parallel and single in on one of them as significant with a p-value of 0.05, it's not really a bulletproof conclusion.

[crackedbassoon]

That study actually did NOT find that Vit D reduced autoimmune disease rate. P=.05 means not significant (it needs to be <.05). Pretty gigantic blunder by the researchers to be honest.