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.
References
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
7 comments:
Reference 7 in your excellent letter is Plasma vitamin D and mortality in older men: a community-based prospective cohort study It says: "Greatly increased enterohepatic cancer death rates were observed with both low and high plasma vitamin D concentrations. [...]Secondary bile acids are formed in the intestine but enter the bile after enterohepatic circulation (19, 34). In contrast, high concentrations of vitamin D suppress the farnesoid X receptor that detoxifies carcinogenic bile acids (12, 20, 21), suggesting a mechanism for increased cancer risk with high vitamin D concentrations. In addition, vitamin D induces osteocalcin (6), which is expressed in pancreatic cancer cells and increases their growth, proliferation, and invasion (35). Also intriguing is the fact that the synthesis and excretion of bile acids were observed to be dramatically elevated in Klotho-deficient mice (36) that ex- hibit altered mineral homeostasis due to high vitamin D activity (11)"
International Journal of Circumpolar Vol 71 (2012).
Occurrence of pancreatic, biliary tract, and gallbladder cancers in Alaska Native people, 1973-2007
. "Conclusions: Pancreaticobiliary cancers, particularly biliary tract and gallbladder cancers, in both AN men and women and pancreatic cancer in women occur at an increased rate in Alaska Native people."
Your critic Grant collaborated with the Garland brothers
October 19, 2010 New clinical trial explores role of vitamin D in preventing esophageal cancer
."researchers are examining if Vitamin D intake is linked to an increase in a protein called 15-prostaglandin dehydrogenase... and cancer"
It seems there may indeed be a connection
Frank C. Garland, Epidemiologist
Who Connected Vitamin D Deficiency and Cancer, Dies "The cause was cancer of the esophageal junction."(He had been ill for a year. Garland advocated, and presumably practiced, supplementation of vitamin D to reach a blood level of 100-150 nmol/L)
Sean,
A lot of people are going overboard on vitamin D in the naïve belief that there is no risk of overdosing. In twenty years time, we'll be reaping a grim harvest. People will be comparing vitamin D therapy to thalidomide.
A not-so-minor point. The vitamin D lobby is getting a lot of money, mainly from the tanning salon industry but also from companies that sell vitamin-enriched products for children and expectant mothers.
Is there any evidences of some sort of synergy between sexual preferences and all sort of makeup and body paintings ?
In some cases, body paints are perfect match for the known sexual preferences and the standard of beauty of their users. It's obvious in China and Japan with the white makeup and the avoidance of sun rays. I don't know about northern Inuits, but all other native amerindians use body paints.
In Africa, same thing, which suggests that body painting or 'enhancement' is a very old human behavior. Havn't we found dyes associated with Neandertal tools? It's not a big stretch to suggest they also used body paintings.
Maybe these behaviors did more than just 'reveal' a taste for a particular physical trait, maybe they have also reinforced the sexual preferences of early humans and therefore have acted in synergy with sexual selection. Not to mention that painting a face white and avoiding the sun is not very good for vitD synthesis. How evolutionarist explain these counterintuitive behaviors?
My bet is that these body enhancements, including more extreme body modifications, such as neck elongation in Africa or the shortening of the feet in Japan, reveal ancient preferences for neotenic/pedomorphic traits that have been exagerated in some cases.
But maybe it's too big a topic to be discussed here.
The trouble is that people have this idea of north latitudes, where solar UV is too weak for solar synthesis of vitamin D, as being inhabited by Inuit who lived on marine food rich in vitamin D. The existence of Amerindians who lived at similar high latitude while consuming meat, but no foods of marine origin, is unknown to most.
Ignoring the fact that Europe is within the zone where UV-B mediated skin synthesis of massive amounts of fat soluble (storable) vitamin D occurs for months of the year, we are told that the dark skinned European hunter gatherers of the stone age got their vitamin D from meat; it is claimed that "there is plenty of vitamin D in fresh meat" But did the meat of prey animals provide vitamin D for European hunter gatherers?
Circumpolar Health (2012) Level of selected nutrients in meat, liver, tallow and bone marrow from semi-domesticated reindeer (Rangifer t. tarandus L.) "Vitamins D2 and D3 were neither detected in meat nor in any of the studied tissues"
Ben,
Body paint can be used for different uses. It can be used to enhance sexual attractiveness, but it can also be used to present a more intimidating, even terrifying appearance.
Richard Russell has found that female cosmetics seek to increase the contrast in luminosity between facial skin and the lips and eyes. This is a universal tendency that probably corresponds to an innate algorithm for sex recognition. I suspect that most cases of body painting are attempts to hyperstimulate a mental algorithm of one sort or another.
Red ochre seems to have been commonly used by early modern humans. It may have been used to make men look more masculine (male skin has more hemoglobin than female skin). Or there may have been some other reason.
Sean,
There's a lot of interest now in the subject of vitamin D and northern Natives. I'm discovering that I'm not the only one who is worried about attempts to "correct" the low vitamin D levels of these peoples.
RS, the dates for white skin genes cited by Peter show European hunter foragers did not have white skin. So they had no need for extra vitamin D. Hunter gatherers don't get diseases of civilization. OK, but as as the post above shows populations adapted to extremely high latitude hunter gathering have adaptations to LOW vitamin D levels. lack of circulatory disease is likely due to foragers being active and not getting fat.
So improving your health, by having a level of vitamin D like a hunter gatherer, does not entail raising your blood level of vitamin D level to double the average (for people of your your ethnic background). And to seal the deal, advice from the massive report by the Institute of Medicine's 14 experts is not to take vitamin D supplements.
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