Pigment genes not skin pigmentation affect UVB-induced vitamin D

Skin pigmentation is believed to contribute to the generally low serum 25-hydroxyvitamin D (25(OH)D) concentrations observed in darker-skinned persons. The influence of measured skin pigmentation on UVB-induced 25(OH)D increase was investigated together with 9 demographic and 13 genetic parameters (pigment SNPs). Forty participants representing a wide range in measured skin pigmentation were exposed to identical UVB doses on identical body areas over nine weeks with weekly measurements of serum 25(OH)D. This study took place in Denmark during winter, a period with negligible ambient UVB, so variation in 25(OH)D synthesis was not influenced by latitude, season, sun and clothing habits. The increase in 25(OH)D concentration displayed considerable variation (range: 2.9 to 139 nmol L-1). Constitutive and facultative skin pigmentation exerted separate influence on the variation of the UVB-induced linear 25(OH)D increase. However, this influence was statistically non-significant in the presence of separate significant pigment SNPs. The variation in the 25(OH)D increase in the combined linear model was not explained by measured skin pigmentation but by sex, height, age and seven SNPs located in the ASIP, MTAP, MIR196A29 and Solute Carrier Family genes. This linear model including individual intercepts and the 10 parameters influencing the slope explained 77.4% of the variation. This study confirmed the influence of sex, age and height on 25(OH)D increase and found that pigment genes provided a better relation to UVB-induced 25(OH)D increase compared to the actual measured skin pigmentation. Therefore, only investigating skin pigmentation obscures other causal parameters for low 25(OH)D.