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Reply to W.B. Grant ‘Re: Vitamin D deficiency among northern Native Peoples’

Authors
Journal
International Journal of Circumpolar Health
1239-9736
Publisher
Co-Action Publishing
Publication Date
Volume
71
Identifiers
DOI: 10.3402/ijch.v71i0.18435
Keywords
  • Letter To The Editor
Disciplines
  • Anthropology
  • Medicine

Abstract

doi:10.3402/ijch.v71i0.18435 Reply to W.B. Grant ‘Re: Vitamin D deficiency among northern Native Peoples’ Peter Frost* a/s Bernard Saladin d’Anglure, De´partement d’anthropologie, Pavillon DeKoninck, Universite´ Laval, Que´bec, QC, Canada Dear Editor: Dr. Grant seems to assume that all humans share the same vitamin D metabolism, an assumption that is doubtful even on theoretical grounds (1). We know that natural selection can alter the way the human body synthesises, transports and uses this vitamin. We also know that the relevant selection pressures (from solar UV and skin color) vary from one human population to the next. So it is not necessarily unhealthy for a population to have low blood levels of vitamin D. The underlying metabolism may simply be different. Vitamin D levels are normally low not only in northern Natives but also in other darker-skinned humans, even those who still live in the tropics and are routinely exposed to strong solar UV (2). Indeed, if we look at the human species as a whole, the outlier actually appears to be lighter-skinned humans and their relatively high levels. This outlier, however, also tends to decide what is medically normal and what is not. Therein lies part of the problem. Why do these differences in metabolism exist? At present, we can only speculate. Lighter-skinned humans can more easily synthesise vitamin D on their own and may thus use it less efficiently. Conversely, darker-skinned humans may have had to ration its use and develop alternate metabolic pathways. This has been especially true at high northern latitudes, where solar UV is too weak for synthesis in the skin. An alternative is to consume fatty ocean fish, but this food source was formerly available only in coastal regions. The interior of Alaska and northern Canada had few natural sources of vitamin D. Over time, northern Natives should have adapted to this situation through natural selection. And they had time: so

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