Increased 25(OH)D3 Level in Redheaded People: Could Redheadedness Be an Adaptation to Temperate Climate?

In a study involving 73 redheaded and 130 non-redheaded individuals, researchers found that redheaded participants had higher levels of the vitamin D precursor 25(OH)D3 (calcidiol) in their blood serum, while maintaining similar folic acid levels compared to non-redheads. The study also observed that 25(OH)D3 concentrations in redheads correlated with the intensity of their hair color, as measured by spectrophotometric methods and assessments by both the participants and independent observers. Unlike non-redheads, whose 25(OH)D3 levels varied with sun exposure and suntan intensity, redheads' levels appeared to be influenced by physiological differences rather than behavior. Additionally, folic acid levels were found to increase with age and baldness intensity, but decrease with the frequency of visiting tanning salons. These findings suggest that the redheaded phenotype may be an evolutionary adaptation that allows for efficient synthesis of vitamin D in regions with lower UVB radiation, such as central and northern Europe.