Increased calcidiol level in redhaired people: Could redheadedness be an adaptation to temperate climate?

Abstract

About 1-2% of European population are redhaired, meaning they synthesize more 19 pheomelanin than eumelanin, the main melanin pigment. Several mutations could be 20 responsible for this phenotype. It has been suggested that corresponding mutations spread in 21 Europe due to a founder effect shaped either by a relaxation of selection for dark, UV-22 protective phenotypes or by sexual selection in favor of rare phenotypes. In our study, we 23 investigated the levels of vitamin D precursor calcidiol and folic acid in the blood serum of 24 73 redhaired and 130 non-redhaired individuals. In redhaired individuals, we found higher 25 calcidiol concentrations and approximately the same folic acid concentrations as in non-26 redhaired subjects. Calcidiol concentrations correlated with the intensity of hair redness 27 measured by two spectrophotometric methods and estimated by participants themselves and 28 by independent observers. In non-redhaired individuals, calcidiol levels covaried with the 29 amount of sun exposure and intensity of suntan while in redhaired individuals, this was not 30the case. It suggests that increased calcidiol levels in redhaired individuals are due to 31 differences in physiology rather than in behavior. We also found that folic acid levels 32 increased with age and the intensity of baldness and decreased with the frequency of visiting 33 tanning salons. Our results suggest that the redhaired phenotype could be an evolutionary 34 adaptation for sufficient photosynthesis of provitamin D in conditions of low intensity of UV-35 B radiation in central and northern parts of Europe.36