The Vitamin D Hypothesis (VDH) purports to explain the range of skin colors observed between races/ethnies around the world. Since there are little UVR and even less vitamin-D-producing UVB in the northern hemisphere, other ways of producing/getting ample amounts of vitamin D were imperative for survival. Locations such as the far north were uninhabited up until 12,000 years ago—the explanation being that populations didn’t have the culture to survive such harsh conditions (see Goebel, 1999; Bergman et al, 2004). However, a more likely reason was that there were biological limits on the production of vitamin D due to the lack of UVB rays for most of the year. In this article, I will discuss the skin color of Arctic peoples and why it does not follow the simple gradient of UVB around the world.
To overcome the biological limitations of little to no UVB throughout the year, they needed to supplement with foods to get ample amounts of vitamin D—to cover what they did not get from the weak UVB rays. To overcome the limitation of their environment and vitamin D production, they had to consume fatty animals who had ample stores of vitamin D in their systems. The types of foods allowed peoples to live so far north, since there were little vitamin-D-producing UVB rays, lifestyle and culture is how we conquered the unforgiving far north.
Peoples like the Inuit and Saami eat a diet that is high in vitamin D. Inuits, for example, eat a diet high in vitamin D and n-3 fatty acids (Schaebel et al, 2015). Due to the high vitamin D intake from their diet, they were able to supplement what they did not get from the sun in their diet and thusly were able to live in the unforgiving cold north due to their diet high in vitamin D (Deng and Xu, 2018). Their dark skin color can be explained in a few ways: their diet (high in vitamin-D-rich marine mammals), UVB rays bouncing off ice, snow, and water, and they are recent migrants to those climes, which would explain their darker skin color compared to other populations that have evolved for a longer time in these climates (Jablonski and Chaplin, 2002).
When people look at Arctic people such as the Inuit, they look at their skin color and see the amount of UVB rays they receive during the year and presume that the VDH is wrong because, according to the VDH, Arctic peoples should have the lightest skin but have dark skin—compared to others who evolved recently in those latitudes—but they have dark-ish skin for that latitude. The answer is simple: they were able to consume enough vitamin D in their diet—a lack of vitamin D production/consumption was one barrier to living in the far north which was then overcome with culture and the foods peoples eat.
The environment of the Arctic is dim and dark for most of the year, though during the summer, of course—when they are most active—they are bathed in solar radiation which is then reflected by the snow, ice, and water. Fresh white snow reflects 94 percent UVA rays and 88 percent of UVB rays. Chadysiene and Girgzdys (2008; 87) write:
The average data of experimental measurements show that maximum albedo of UVA radiation (of about 94%) was at 1 p.m. in comparison with albedo of UVB radiation of about 88% at 2 p.m. The measurements of albedo were performed on fresh snow with big crystals.”
For example, Inuit populations in northern Greenland report spending up to 16 hours outdoors in the spring and summer months, and would be exposed to UV rays bouncing from ice, snow, and water (Andersen, Jakobsen, and Laurberg, 2012). Exposure to UV rays for this extended period of time—along with eating a diet high in vitamin D—is enough to explain their skin color.
Clearly, Arctic people get bathed in UVB and UVA rays from being reflected off the snow and ice, which gives them their darker skin color. They have the ability to tan (which is distinct from the American term “tanning”) and their tanning ability protects them from high doses of UVR that are reflected from the snow whereas their diet high in vitamin D gives them their darkish skin color and allows them to remain healthy in such a harsh, unforgiving environment.
Nina Jablonski has been writing about the VDH for about 30 years. Jablonski writes in her book Living Color: The Biological and Social Meaning of Skin Color (2012: 68):
Traditional cultures of the Inuit and the Saami center on harvesting vitamin-D-rich foods. The dietary focus for both groups has compensated for the vitamin D they cannot produce in their skin. Both peoples remain healthy when they stick to their traditional diets but suffer badly from vitamin D deficiencies when they switch to Western diets that are lower in vitamin D.
Here’s the thing: when these populations move away from their natural, vitamin-D-rich diet, they suffer from many deficiencies regarding vitamin D, even today many Inuit populations suffer from vitamin D deficiency, both children, and adults (Hayek, 2011). So the change in the Inuit diet is the cause of these deficiencies—their traditional diet was high in vitamin D, but their new diet (the Western diet) is low in vitamin D; since they have dark skin and the UVB is so variable throughout the year, they then suffer from vitamin D deficiencies (Sharma et al, 2011). Sharma et al (2011: 475) conclude that Arctic people are at-risk for vitamin D deficiency due to lack of UVB exposure, moving away from a traditional diet high in vitamin D to a Western diet low in vitamin D, combined with their dark skin.
Frost (2012) claims that while the explosion of rickets in Arctic populations is due to a change in diet (shifting away from a high meat diet) and “increased consumption of certain reactive substances: phytic acids in commercially processed cereals; sodium bicarbonate in baking soda; and aluminum hydroxide in antacids” (Frost, 2012). The dominant source of vitamin D for the Inuit is their diet (Schaebel et al, 2015), and so, due to their shift away from their natural diet high in fatty fish and vitamin D, once they began eating a diet not ancestral to them, then the maladies began. We can see this with every country/population that begins to eat a new diet full of processed foods.
Since the frequency of rickets has exploded in populations that eat a Western-like diet and not their traditional diet, this implies that the traditional diet provided enough vitamin D, and when they began eating a new diet with less vitamin D, then these problems such as rickets occurred.
To end these implications, the Inuit need to return to consuming a traditional diet, since their traditional diets have the adequate vitamins and minerals needed to survive in the environment they are currently in (Koladhooz et al, 2013). Higher BMI (body mass index), their skin color, and the latitude of where they live contribute to low vitamin D production. Inuits who consumed a low number of traditional food items were more likely to be deficient in vitamin D (Anderson et al, 2013) while this deficiency is seen even in Inuit school children (Hayek, Egeland, and Weiler, 2010; Singleton et al, 2015).
In sum, there is no anomaly regarding the skin color of Arctic peoples; the hypothesis is called “the vitamin D hypothesis”, and so they get ample vitamin D from the reflection of UV rays from the snow, ice, and water. Reasons for the darkness of their skin include the fact that they are recent migrants to those locations, they consume a diet high in vitamin D, and the reflection of UV rays from albedo surfaces.
The hypothesis that UVB exposure explains the observed skin gradients predicted a novel fact—that populations that migrated out of Africa would be seen to have light skin. This occurred multiple times through three different molecular pathways, in the Neanderthals (Lalueza-Fox et al, 2007) and Europeans and East Asians (different molecular mechanisms for them; Norton et al, 2007). This was a risky, successful and novel prediction made by Jablonski and Chaplin (2000). That this does not hold for Arctic people is not a blow to the hypothesis; it is perfectly explained by the bouncing of UVR off of albedo surfaces and a high vitamin D diet. Skin color is an adaptation to UV rays.