Racial pigmentation and the cutaneous synthesis of vitamin D

• The varying epidermal melanin content that produces racial pigmentation determines the number of photons that reach the lower (malpighian) cellular layers, where vitamin D₃synthesis takes place. We investigated the effect of racial pigmentation on vitamin D₃formation, stimulating the process with a fixed dose of UVB radiation (wavelengths, 290 to 320 nm). Vitamin D nutritional status was further assessed measuring serum 25-hydroxyvitamin D and the most active serum metabolite, 1,25-dihydroxyvitamin D. Experimental subjects were young (third decade of life) and healthy, representing the white, Oriental (East Asian), Indian (South Asian), and black races. Basal serum vitamin D₃levels were similar among groups, ranging from 2.3±0.6 nmol/L (mean±SEM) for blacks to 3.4±1.0 nmol/L for Indians. Following whole-body exposure to 27 mJ/cm²of UVB, there was a significant racial group effect on serum vitamin D₃levels. Post-UVB levels were significantly higher in whites (31.4±4.4 nmol/L) than in Indians or blacks (12.8±2.9 and 9.1±2.1 nmol/L, respectively), while the levels in blacks Orientals (27.8±4.4 nmol/L) differed significantly from those in blacks and Indians but not in whites. Race had only a marginal effect on serum 25-hydroxyvitamin D, with higher levels in whites than in blacks (69.9±12.7 vs 29.7±6.2 nmol/L). Serum 1,25-dihydroxyvitamin D and vitamin D binding protein levels were similar in all groups. We conclude that while racial pigmentation has a effect, it does not prevent the generation of normal levels of active vitamin D metabolites.