I have also my own example of N(1) where supplementing vit-D made me healthier and I am nerd sitting most of the time hidden from the sun.

Pre-Covid after start of supplementation I noticed less infections, easier hangovers overall better health.

That said I mostly sit inside by the screen and live in countries where is not that much sun so it is easy for me to get positive outcome of supplementation.

I think there is a lot of people like that and that is why there is so much positive reaction for D supplementation.