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"Evolutionary Argument for Optimal Vitamin D Level"
The Institute of Medicine’s target vitamin D blood level corresponds with what one finds out in the general population.
Normal people getting about an hour of sun a day have about 20 to 30 (ng/ml). This is in nmol/l, 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, however, interpret this data differently, suggesting that the vitamin D "levels in the lifeguards are normal and the "normals" are actually vitamin D deficient."
We did, after all, apparently live as naked creatures in the East African tropics for about a million years before we began using 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 allies of smog ridden cities did rickets rear it’s ugly head and we had to start fortifying our foods supply with D.
So instead of a blood level of 20, maybe we should shoot for what farmers in Puerto Rico, or lifeguards in Israel and St. Louis.
Just because those levels might really be more normal for our species, though, doesn’t necessarily mean that they’re the best.
There’s a reason people tan: that’s your body producing melanin to protect itself; there’s a reason we as a species 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.