Evolutionary health aficionados of all varieties, ranging from Darwinian medical researchers to evolutionary nutritionists to organic fitness enthusiasts, have long recognized that sun exposure is critical in the context of health promotion/disease prevention, in large part because it brings about the generation and build-up of vitamin D inside our bodies, which is known to be involved in a number of physiological processes related to immune function, bone formation, and cognition.
But how much vitamin D do we really need: what’s the required or optimal dose?
Where should we direct our focus as we search for clues as to how much vitamin D we’ve evolved to require to function at our best?
Within the aforementioned evolution-oriented group, it’s widely recognized that the amount of 25-hydroxyvitamin D (also known as 25(OH)D or calcifediol) – a predominant circulating form of vitamin D that’s commonly used as an indicator of vitamin D status – that’s present in the bloodstream of the typical modern man is wholly inadequate to support optimal health and that this is part of the reason why a number of chronic diseases run rampant in contemporary human societies. The recommendations of melanoma-fearing sun-shunners who’ve been telling people to smear on sunscreen, cover up, and avoid the sun when possible are viewed with skepticism, in large part because they conflict with evolutionary logic.
Throughout our evolution, sunlight has been intrinsic to the human milieu, which up until quite recently consisted of trees, birds, and wild ungulates, as opposed to skyscrapers, supermarkets, and roads made of concrete. It has long stimulated the production of ample amounts of vitamin D3 in human skin, in addition to influencing a number of other important physiological processes. A vitamin D supplement or fatty fish certainly isn’t a fully satisfactory alternative to sunlight in this respect.
This is not so say that it’s good to bathe under the hot midday sun for many hours every day or that we shouldn’t try to avoid getting burned; however, there’s no doubt that we need a bit of sun to be our best selves and optimize our vitamin D levels. It’s not a straight-forward task to elucidate exactly how much vitamin D we’ve evolved to require though, in part because we vary with respects to our evolutionary legacy and health status, among other things. Whereas some people are northerners in their descent, others naturally belong to groups who’ve longed occupied temperate areas of the world.
With that being said, ultimately, we’re all of African descent: products of a long evolutionary process that largely took place near equator, under the hot African sun. In other words, it would certainly be interesting to know where Africans who still adhere to traditional diet and lifestyle practices stand with respects to their vitamin D status.
Clues from Africa
Some years back, a group of perceptive evolutionary thinkers – Martine F. Luxwolda, Remko S. Kuipers, Ido P. Kema, D. A. Janneke Dijck-Brouwer, and Frits A. J. Muskiet – took it upon themselves to measure the vitamin D concentrations of indigenous populations in East Africa. More precisely, they extracted blood samples from twenty-five Hadzabe hunter-gatherers and thirty-five pastoral Maasai and then proceeded to quantify the mean serum level of 25-hydroxyvitamin D.
The following quote from the introduction of the study encapsulates the authors’ rationale for conducting the investigation:
The sum of serum 25-hydroxyvitamin D2 and D3 (25(OH)D) concentrations [of traditionally living East Africans] might provide us with information on a favourable vitamin D status for overall health from a Darwinian perspective. (1)
Later on, they proceed to share the results of the study, which they summarize as follows:
The mean 25(OH)D values of these populations, i.e. Maasai and Hadzabe, were 119 and 109 nmol/l, respectively. None of these populations had values below 50 nmol/l. The highest values were 167 and 171 nmol/l, respectively, which are well below the estimated toxicity concentrations of 250 and >600 nmol/l. (1)
Also, of note, they then go on to compare their findings with those of other studies; a comparison that helps put the detected vitamin D values into perspective. Here’s this juxtaposition:
The presently encountered status is comparable with 25(OH)D concentrations above 100 nmol/l as measured in Caucasian lifeguards who had been working for at least 4 weeks at an open-air swimming pool in St Louis during May and June and Hawaiians receiving more than 3 h of sun exposure per d for more than 5 d/week during at least 3 months. (1)
Finally, before wrapping up, they get into a discussion about what may constitute ideality with respects to vitamin D status. At the end, they point out the following:
We conclude that people with traditional lifestyles, living in the cradle of mankind, have a mean circulating 25(OH)D concentration of about 115 nmol/l. Whether this concentration is optimal under the conditions of the current Western lifestyle is uncertain, but it may serve as a target for further research. Such investigations should preferably be conducted with concomitant appreciation of many other important factors in Ca homeostasis that we have changed since the industrial revolution. (1)
Why this information is important
There are a number of reasons why I think this study deserves more attention than it’s been getting. First of all, it helps draw attention to the fact that we evolved in the presence of sunlight, which has historically been our principal “source” of vitamin D, and hence, that it’s irrational, from a Darwinian point of view, to assume that we would do best to minimize our sun exposure.
Secondly, it provides clues as to what
With that being said, the mean vitamin D concentration of traditional Africans is indicative of the level that would have been typical throughout much of our evolution, and hence, the level that the human physiology would have grown accustomed to over millions of years. Hence, it’s not unreasonable to speculate that such a level may indeed represent optimality in many, if not most or even all, instances. As pointed out by the authors of a 2016 paper (5), this idea is invigorated by studies linking such a high vitamin D concentration with lowered disease risk. Here’s what they posit on the basis of recent research on the relation between different vitamin D levels and health:
This level [the vitamin D concentration of the Hadza and the Maasai] could serve as a target of optimal vitamin D status that was built during millennia of human evolution, controlled by natural selection rules. It seems that such optimal level was fixed during human migration out of the equatorial Africa (since ~100,000 years ago) that forced loss of skin pigmentation in populations living out of the tropics. Thus, lighter skin is a result of adaptation to low UVB intensity that allows the same vitamin D synthesis which previously occurred in the tropics. (5)
Other researchers have made similar suggestions, as highlighted by the quote below, pulled from a 2006 paper entitiled What is the optimal vitamin D status for health?
Human biology was probably optimized through natural selection for a sun-rich environment that maintained serum 25(OH)D higher than 100 nmol/L. (6)
Thirdly, when combined with other research, the study by Luxwolda et al. highlights that there’s a marked difference between the vitamin D concentrations of traditional populations who reside in what has been referred to as “the cradle of mankind” and people living in an industrialized milieu. In the U.S., it’s been shown that the mean total 25(OH)D concentration is about 68 nmol/L in children and adults (2, 3), which is obviously a lot
Last but not least, in combination with the above insights, the study by Luxwolda et al. may help us figure out what constitutes a prudent approach to sun exposure and vitamin D intake. The authors of the 2016 study mentioned above get into that issue and use the results from the study on the Hadzabe and Maasai as the basis for determining vitamin D3 effective daily doses for
Key takeaway points
Deep down, in our genes, we’re all Africans. Given that so much of our evolutionary journey took place in a natural environment close to