Size of the exposed body surface area, skin erythema and body mass index predict skin production of vitamin D

Background: Cholecalciferol (vitamin D-3), produced in the skin by UVB irradiation (290-315 nm) of 7-dehydrocholesterol, is metabolized in the liver into 25-hydroxyvitamin D [25(OH)D] which is a major circulating metabolite. Aim: To examine changes in serum concentrations of cholecalciferol and its metabolites after UVB exposure of different skin areas. Methods: 21 healthy Caucasians (skin type II and III, aged 23-47 years) were exposed to broadband UVB (290-320 nm) and randomized to either exposure to one minimal erythema dose given as a single dose, or a suberythemic dose given for 3 subsequent days. The following areas were exposed: face and back of hands, upper half of the body and the whole body, respectively. Serum cholecalciferol and 25(OH)D were measured immediately before start and 24 h after the 1st and last exposure, respectively. Results: Subjects with whole body exposure had an average S-cholecalciferol increase per dose unit of 0.18 ng m1(-1) mJ(-1) cm(2), 0.95 CI: (0.16, 0.20), upper body treatment 0.13 ng ml(-1) mJ(-1) cm(2), 0.95 CI: (0.10, 0.15) and face and hands exposure 0.013 ng ml(-1) mJ(-1) cm(2), 0.95 CI: (-0.012, 0.037). The increase in cholecalciferol correlated positively to the UVB dose and skin erythema and negatively to body mass index (BMI) when controlling for other factors. Exposure of face and hands induces smaller cholecalciferol production in comparison with exposure of larger skin areas. Conclusion: Size of the exposed skin area, UVB dose, skin erythema and BMI were the major determinants for serum levels of skin synthesized cholecalciferol. Exposure of hands and face induces smaller cholecalciferol production in comparison with exposure of larger skin areas. (C) 2015 Elsevier B.V. All rights reserved.