I assume the lifeguards were caucasian? With a “built in” SPF of 15 what blood level of Vit D does the lifeguard of African descent attain? Perhaps that is a better clue for evolutionary “normal”.
CapeBreton / Originally Posted in Evolutionary argument for optimal vitamin D level
You’re absolutely right, CapeBreton. Considering the average vitamin D levels of clothed high latitude office workers “normal” for our species doesn’t make much sense and though lifeguards are at least outside all day and half naked, they were still both Caucasian and Missourian. A more representative normal level of the “sunshine vitamin” could be gleaned measuring levels in those with black skin who live scantily clad in equatorial Africa. The problem is that such a study has never been done–until now.
This month researchers published results from the Maasai and the Hadzaben and the title says it all: “Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l.” So lower than the pale St. Louisans, but still nearly twice the levels found in most Americans. No change to my recommendations, though, summarized in the culmination of my two week vitamin D series: Resolving the vitamin D-bate.
Image credit: Steve Slater (Wildlife Encounters) / Flickr