Early winter afternoon in Tromso, Norway (source). There is little or no solar UV for vitamin D synthesis at high northern latitudes. Humans have had to adapt accordingly.
I’ve published another article on vitamin D metabolism and northern Native peoples. It’s actually a reply to a letter criticizing my initial article.
A few extracts:
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.
[…] 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: some 15,000 years in Arctic North America and longer still if we include their remote ancestors in Beringia and northern Eurasia. Natural selection also had many possible ways to make their bodies less dependent on vitamin D: receptors that bind this molecule more strongly; greater storage in the body and better transport in the bloodstream to target tissues; increased uptake of calcium and phosphorus through alternate metabolic pathways, etc. Indeed, the Inuit show high uptake of calcium despite low levels of vitamin D.
Comments are welcome.
Frost, P. (2012). Reply to W.B. Grant ‘Re: Vitamin D deficiency among northern Native Peoples’International Journal of Circumpolar Health,71, 18435 - DOI: 10.3402/ijch.v71i0.18435 http://www.circumpolarhealthjournal.net/index.php/ijch/article/view/18435/pdf_1