Oktawia Borecka, John Dutton, Jonathan Tang, William D. Fraser, Lesley E. Rhodes

British Journal of Dermatology · 2023

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Abstract

Abstract Skin exposure to ultraviolet radiation (UVR) triggers conversion of precursor 7-dehydrocholesterol (7DHC) to vitamin D3, which then enters the bloodstream. The aim of this study was to assess if skin 7DHC concentration differs between younger and older adults, and to explore the impact of solar-simulated UVR (SSR) on 7DHC (in skin) and vitamin D3 (cholecalciferol; in serum) in these age groups. Younger (n = 10, 18–40 years) and older (n = 11; 65–89 years) adults of skin phototype I–III were exposed to a suberythemal dose of SSR (95% UVA, 5% UVB, 1.3 standard erythemal dose) over 35% body surface area in the UK winter. Six 5-mm buttock skin punch biopsies were taken: two from unexposed skin, two immediately post-UVR and two at 24 h post-UVR. Blood was taken at baseline, 24 h and 7 days post-UVR. Skin and serum samples were assayed using high-performance liquid chromatography–tandem mass spectrometry. Baseline mean (SD) 7DHC concentrations were 0.22 (0.07) µg mg–1 and 0.25 (0.08) µg mg–1 in younger and older adults, respectively. Immediately post-UVR, 7DHC concentrations were 0.27 (0.10) µg mg–1 and 0.22 (0.08) µg mg–1 in younger and older adults, respectively, and 24 h post-UVR they were 0.27 (0.08) µg mg–1 and 0.28 (0.13) µg mg–1, respectively. Baseline serum vitamin D3 concentrations in younger adults were 1.5 (1.5) nmol L–1 vs. 1.5 (1.7) nmol L–1 in older adults; 24 h post-UVR they were 3.1 (2.0) nmol L–1 in younger adults vs. 2.5 (2.0) nmol L–1 in older adults and 7 days post-UVR they were 2.0 (2.1) vs. 1.7 (1.2) nmol L–1, respectively. No significant difference was seen in any parameter between age groups. Thus, in contrast to previous assumptions, skin 7DHC concentration is not a limiting factor for vitamin D3 synthesis in healthy older adults relative to younger adults. The early vitamin D3 biosynthetic pathway does not appear to differ between these age groups.