Should the vitamin D levels found in lifeguards be considered the norm for our species given the fact that we evolved running around naked all day in equatorial Africa?
Images thanks to the US National Library of Medicine and daryl_mitchell.
The Institute of Medicine’s target vitamin D blood level corresponds well with what one finds out in the general population. Normal people getting about an hour a sun a day have about 20 to 30 (ng/ml). This is in nanomoles per liter, which corresponds to about 27 ng/ml, whereas lifeguards who spend more like 8 hours in the sun every day have abnormally high levels, like over 60. Others interpret this data differently, suggesting that the vitamin D levels in the lifeguards are the ones that are normal and the quote unquote "normals” are actually vitamin D deficient.
We did, after all, live as naked creatures in the East African tropics for about a million years before we began to use animal skins as capes to cover our shoulders. But tailored clothing, something like we know it today, was not devised until about 40 000 years ago when needles first appear in the archaeological record. The invention of tailored clothing may have been an important factor enabling the first modern human beings to settle permanently in Europe with its cold winters about 30 000 years ago. In Africa there was plenty of sunshine and plenty of vitamin D. Not so in Europe, where there were long winters and people were covered in clothing. This must have been when our species first began to evolve a lighter skin as an adaptation to the shortage of sunshine and vitamin D." It wasn’t until we started living in the sunless alleys of the smog ridden cities did rickets rear it’s ugly head and we had to start fortifying our food supply with D.
So instead of a blood level of 20, maybe we should shoot for what farmers in Puerto Rico get, or lifeguards from Israel or St. Louie.
Just because those levels might really be normal for our species, doesn’t necessarily mean, though, that they’re the best. There’s a reason people tan, that’s our body producing more melanin to protect itself; there’s a reason we evolved with a built-in SPF-15 in our beautiful black African skin. So while maybe normal now is too low; maybe normal then was too high.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by veganmontreal.
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Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. This is the second video in a nine day series on vitamin D. Be sure to check out yesterday's video-of-the-day Vitamin D recommendations changed.
For some context, please check out my associated blog posts: Vitamin D: Shedding Some Light on the New Recommendations and Vitamin D from Mushrooms, Sun, or Supplements?