Differential health gain of summer sunlight exposure in people of different skin types

Public health policy advises limiting summer sunlight exposure, but provides no specific advice for darker-skinned people. This study assessed the relative vitamin D gain on following UK sunlight exposure recommendations in White Caucasians and South Asians. During wintertime (negligible ambient UVB), 86 volunteers (n=70 skin-type II, 16 skin-type V), 20-60y, Manchester, UK, received a simulated summer’s sunlight exposures, comprising 1.3SED, 3 x weekly for 6wks, wearing T-shirt and UV-opaque shorts. Circulating 25(OH)D was evaluated by HPLC (n=60 x II, 10 x V). A 10 x 10 cm2 area of one buttock was left exposed (n=10 x II, 6 x V) and underwent spectrophotometric measurements. At course end, exposed and unexposed skin received an acute 2 x MED challenge, with 24 h measurements. Vitamin D status improved post-course, with significant difference in 25(OH)D gain between types II (mean 10.2, SD 7.5ng/ml) and V (4.6, 1.9), p<0.05. Baseline L* (white-black differentiation) differed between groups, reflecting higher pigmentation of V, p<0.01. The exposures darkened the skin, decreasing L* by 6.2(5.3), p<0.001, with 6% and 24% reduction in II and V respectively, and with strong negative correlation between L* decrease and 25(OH)D gain (R2= 0.94, 0.92; p<0.001). The simulated summer conveyed photoprotection, UV-treated skin demonstrating lower A* values (erythema) than UV protected skin after challenge with 2 x MED, p<0.05, with 14% erythema protection in II and 50% in V. Thus, the same summer exposure conditions cause approximately half the 25(OH)D gain in darker than fair skin-types, with greater pigmentation gain contributing to this. More specific advice on sunlight exposure may be required for people of skin type V living at higher latitude.