I've spoken about Vitamin D a fair amount on this blog before. Not only have I presented it as a major selective pressure for light skin in the northern latitudes after the switch to agricultural lifestyles (and the concomitant nutrient deprivations due to reliance on a predominantly starch diet), but I recently found that I myself suffered from a lack. Though I eat a salad most days, and try to eat meats and fish, the fact that I have dark skin and live at a relatively high latitude and in a region characterized by cloudy winters was a combination which naturally led to low levels of synthesis. I'm taking supplements now, and plan on taking them for a long time. After I found out about my own deficiency I looked up some side effects. You all know about Rickets, but it turned out there were a host of global low level ailments that might be correlated with a lack of this nutrient. Now more evidence, Vitamin D Supplements Appear To Be Associated With Lower Risk Of Death:
Past studies have suggested that deficiencies in vitamin D might be associated with a higher risk of death from cancer, heart disease and diabetes--illnesses that account for 60 percent to 70 percent of deaths in high-income nations, according to background information in the article. "If the associations made between vitamin D and these conditions were consistent, then interventions effectively strengthening vitamin D status should result in reduced total mortality," the authors write. ... Over an average follow-up period of 5.7 years, 4,777 of the participants died. Individuals who took vitamin D had a 7 percent lower risk of death than those who did not. In the nine trials that collected blood samples, those who took supplements had an average 1.4- to 5.2-fold higher blood level of vitamin D than those who did not.
Of course, many of the diseases above hit late in life; evolutionarily they might not have been particularly salient (though I doubt that matters to do you if you are 65 and looking at a few extra healthy years). But I suspect that increased morbidity is simply the margin here, it probably has a non-trivial effect on basal physiological fitness.
