I do think skin color is a factor.

Normally darker skinned people, live in more tropical Southern countries. They don't cover up 100%... either.

In the US darker skinned people tend to have rickets risk more.
This is because the more pigment in the skin blocks some UV...but in their country of origin they are typically outside MORE, so that balances out.

In northern latitudes, darker pigmented people need longer sun exposure therefore.

The Amish are highly inbred too...so that if the original members from many decades ago, were inefficient Vit D synthesizers, that trait would be passed eventually to the whole community. The Amish are often quoted as having less autism for the same reasons, to illustrate that autism may be genetic.

But I do think the coming years will be exciting about Vit D.... and we all need to keep in mind that Vit D is NOT a vitamin...and I hope the name converts to D3 or CholeD3 or something like that. The general public and some older medical doctors think...diet/deficiency...and that is not what is happening.

I do think it is exciting... the new research. And in fact it may turn out to be a medical miracle and turning point in our world!
(won't Big Pharma be fit to be tied?)