EVOLUTIONARY ADAPTATIONS: THE IMPACT OF LIGHTER SKIN:
It would take someone with dark skin of African or South Asian ancestry about 60 minutes at the same time of day to make the amount of vitamin D that a person of European ancestry would make in about 10 minutes, estimates Reinhold Vieth, one of Canada's top vitamin D experts and a professor in the department of nutritional sciences at the University of Toronto.
You probably know of Vitamin D deficiency for rickets, but I think more common ailments might have a major fitness impact:
VDR ligands have also been shown to increase the activity of natural killer cells, and enhance the phagocytic activity of macrophages...Active vitamin D hormone also increases the production of cathelicidin, an antimicrobial peptide that is produced in macrophages triggered by bacteria, viruses, and fungi...Vitamin D deficiency tends to increase the risk of infections, such as influenza and tuberculosis. In a 1997 study, Ethiopian children with rickets were 13 times more likely to get pneumonia than children without rickets
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Interesting, I was born with Rickets, and had bowed legs as a toddler, almost died of pneumonia at ages 2 and 12 and had infleunza every year till my late teens, and colds most of the time - I guess vitamin D is implicated.