Well here’s what I think, it depends on where you are living. Where are your people from? If they are from Scotland and you live significantly further south from Scotland, theres a good chance you are getting too much sun, especially early in life.
As people age their Vit D drops and at that point the deficit in D might outweigh the risk of UV exposure. But whites in their 20s and 30s should have more than enough vit D.
Oh I also think weight is a factor here. Fat cells hoard vit D.
What I found interesting was the story of a Polish chemist who found children living in Warsaw around 1900 were developing rickets whereas rural children were not. I cannot imagine city-life keeping children so much indoors like it does today back then.
Your points make sense too.
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