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Byline: Hima. Gopinath, Kaliaperumal. Karthikeyan, Valeti. Meghana Humans have been anointing their skin with natural colorants since antiquity. Before the advent of modern cosmetics, tattoos and hair dyes, the spectacular [...]

This study investigates the relationship between maternal skin tone and low birth weight among Puerto Ricans, a group with a complex ancestry and skin tones that range from very light to very dark. Using data from a representative sample of Puerto Rican mothers, we assess whether skin tone has different implications for low birth weight in three geographic areas (Puerto Rico; New York City; other eastern states). The analysis shows that skin tone is unrelated to low birth weight in Puerto Rico and New York City. However, in the other eastern states in our sample, mothers with dark skin have a high risk of bearing a low birth-weight infant, relative to mothers with light skin. We interpret our findings in light of differences in the social meaning of phenotypic differences across locales. Keywords: Infant health; Skin tone; Puerto Rico; USA

Since vitamin D nutrition reflects only environment and culture, not food supply, accurate estimates of prehistoric vitamin D nutrition are possible, and their implications can be extrapolated from what we know of certain modern humans. Serum 25(OH)D reflects vitamin D nutritional status; a concentration [is less than] 40 will contribute to osteoporosis. Modern people in sun-rich environments who regularly expose most of their skin surface to the sun are a paradigm for Paleolithic human vitamin D status. Lifeguards, and farmers in the Caribbean consistently exhibit 25(OH)D concentrations exceeding 100 nmol/L. Since the yield of vitamin D within UV-exposed skin attains a self-limiting chemical equilibrium, skin color does not play a role in protecting against vitamin D toxicity. Very black skin requires six times longer than white skin to attain the equilibrium. At least four studies show that full-body exposure to sunlight causes the equivalent of 250 [micro] g vitamin D (10 000 IU) to enter the body. The current adult RDA is 5 [micro] g (200 IU). Beyond 40 [degrees] latitude, the angle of the sun is so low that wintertime UV intensity is insufficient for vitamin D production, and it is much diminished in spring and fall. Dark skin is the natural, default color for humans, because it protects both the skin and circulating nutrients from photodegradation (Jablonski NG, Chaplin G. J Hum.Evol. 2000;39:57-106). The evolution of lighter skin, and the consequent correlation between human skin color and latitude was the result of natural selection for enough vitamin D synthesis to permit human reproduction. In its most severe form, selection pressure was due to rickets. Less severe vitamin D deficiency caused osteomalacia, which progressed, with each pregnancy, causing deformation of the pelvis and miscarriages. The most moderate form of vitamin D insufficiency is now recognized as a cause of senile osteoporosis, which occurs beyond age 60 y. Since senile osteoporosis could not have contributed to natural selection and adaptation, I conclude that osteoporosis in ancient populations was a consequence of environment and culture, and not simply inadequate calcium nutrition.