Annual average exposure to erythema-inducing UV radiation at ground level. Source: Jablonski & Chaplin, 2000. At high northern latitudes, vitamin D can be obtained only from one’s diet, notably fatty fish. Yet many northern native peoples consume little fish. Have they evolved a different vitamin D metabolism?
I’ve just published an article on population differences in vitamin D metabolism, specifically about northern native peoples. Comments are welcome.
Abstract
Vitamin-D deficiency seems to be common among northern native peoples, notably Inuit and Amerindians. It has usually been attributed to: 1) higher latitudes that prevent vitamin-D synthesis most of the year; 2) darker skin that blocks solar UVB; and 3) fewer dietary sources of vitamin D. Although vitamin-D levels are clearly lower among northern natives, it is less clear that these lower levels indicate a deficiency. The above factors predate European contact, yet pre-Columbian skeletons show few signs of rickets—the most visible sign of vitamin-D deficiency. Furthermore, because northern natives have long inhabited high latitudes, natural selection should have progressively reduced their vitamin-D requirements. There is in fact evidence that the Inuit have compensated for decreased production of vitamin D through increased conversion to its most active form and through receptors that bind more effectively. Thus, when diagnosing vitamin-D deficiency in these populations, we should not use norms that were originally developed for European-descended populations who produce this vitamin more easily and have adapted accordingly.
References
Frost, P. (2011). Vitamin D deficiency among northern Native Peoples: A real or apparent problem? International Journal of Circumpolar Health, early view
http://www.ijch.fi/aheadofprint.php
Jablonski, N.G. and G. Chaplin (2000). The evolution of human skin coloration, Journal of Human Evolution, 39, 57-106.
I’ve just published an article on population differences in vitamin D metabolism, specifically about northern native peoples. Comments are welcome.
Abstract
Vitamin-D deficiency seems to be common among northern native peoples, notably Inuit and Amerindians. It has usually been attributed to: 1) higher latitudes that prevent vitamin-D synthesis most of the year; 2) darker skin that blocks solar UVB; and 3) fewer dietary sources of vitamin D. Although vitamin-D levels are clearly lower among northern natives, it is less clear that these lower levels indicate a deficiency. The above factors predate European contact, yet pre-Columbian skeletons show few signs of rickets—the most visible sign of vitamin-D deficiency. Furthermore, because northern natives have long inhabited high latitudes, natural selection should have progressively reduced their vitamin-D requirements. There is in fact evidence that the Inuit have compensated for decreased production of vitamin D through increased conversion to its most active form and through receptors that bind more effectively. Thus, when diagnosing vitamin-D deficiency in these populations, we should not use norms that were originally developed for European-descended populations who produce this vitamin more easily and have adapted accordingly.
References
Frost, P. (2011). Vitamin D deficiency among northern Native Peoples: A real or apparent problem? International Journal of Circumpolar Health, early view
http://www.ijch.fi/aheadofprint.php
Jablonski, N.G. and G. Chaplin (2000). The evolution of human skin coloration, Journal of Human Evolution, 39, 57-106.