N=1 but I've felt that I always sleep better when I've spent an hour in the sun that day. Considering how the sun has been a constant during much of human evolution, it just makes sense that our biological processes, both known and unknown, should revolve around it.
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The obvious thing is that white people are white because they lost natural sunscreen living far from the equator. For that to have occurred the selection pressure must have been fairly strong.
Of course we do know that very heavy sun exposure and especially sunburn can cause cancer. It’s probably a case of moderation being good for you— not too little and not too much.
While I largely agree and I think it's pretty heavily sun related: there are plenty of other plausible mechanisms, I don't think it's quite that obvious or clear-cut.
E.g. it snows more as you go towards the poles. There are a lot of pale creatures in climates with snow, for the even more obvious natural selection pressure of "can hide better".
I think the big question is does it matter outside of vitamin d deficiency.
Severe vit d deficiency obviously is strongly negatively selective. So that by itself explains the evolution of white skin in northern climates. I dont think evolution can be used as evidence for other benefits, since vit d deficiency would cause that just by itself.