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

In a study involving 73 redhaired and 130 non-redhaired European individuals, researchers found that redhaired individuals had higher levels of the vitamin D precursor calcidiol in their blood serum, regardless of sun exposure or suntan intensity, suggesting a physiological difference rather than behavioral. The study also observed that folic acid levels were similar between redhaired and non-redhaired subjects, but increased with age and baldness intensity, and decreased with more frequent visits to tanning salons. The correlation between hair redness and calcidiol levels, measured by spectrophotometric methods and assessments by participants and observers, led to the suggestion that redheadedness may be an evolutionary adaptation to synthesize sufficient vitamin D in regions with lower UV-B radiation, such as central and northern Europe.