Increased Calcidiol Level in Redhaired People: Could Redheadedness Be an Adaptation to Temperate Climate?

The study conducted in 2019 investigated the levels of vitamin D precursor calcidiol and folic acid in the blood serum of 73 redhaired and 130 non-redhaired individuals. The results showed that redhaired individuals had higher calcidiol concentrations, with levels correlating with the intensity of hair redness. These levels did not vary with sun exposure or suntan intensity, suggesting that the increased calcidiol levels in redhaired individuals are due to physiological differences rather than behavior. Folic acid concentrations were found to be approximately the same in both groups, but increased with age and the intensity of baldness, and decreased with the frequency of visiting tanning salons. The findings suggest that the redhaired phenotype could be an evolutionary adaptation for sufficient photosynthesis of vitamin D in conditions of low intensity of UV-B radiation in central and northern parts of Europe.