Impact of skin pigmentation on rate of rise of serum 25OHD following simulated sunlight exposures to habitually exposed skin sites

Exposure of skin to UVB in sunlight increases serum 25-hydroxyvitamin D (25OHD) concentration in people of both light and dark skin types. However, human intervention studies of impact of pigmentation on the vitamin D biosynthetic pathway have employed various skin sites, UVR emission and protocols, with conflicting results. Thus, the influence of skin pigmentation remains unclear. We performed an intervention study in healthy volunteers (aged 20-60 yrs) of different skin colour. A total of 109 white Caucasians (skin type I-IV) and 15 South Asians (type V) received simulated summer sunlight exposures, 1.3 SED 3-times weekly (95% UVA, 5% UVB). Irradiations were in a whole body irradiation cabinet with subjects wearing T-shirt and shorts to reveal commonly exposed skin sites (approx. 35% surface area). Blood samples were taken weekly for serum 25OHD assay and data for 3 weeks of irradiations were analysed by repeated measures analysis of variance. Serum 25OHD levels increased in the white Caucasian group from mean (SD) 17.6 (7.6) ng/mL at baseline to 25.4 (6.3) ng/mL at 3-weeks and in the S. Asian group from 6.4 (1.9) ng/mL at baseline to 9.7 (2.8) ng/mL. Analysis revealed the increase in serum 25OHD over the course of exposures was significant (p