Vitamin D production after UVB exposure – A comparison of exposed skin regions

• Serum cholecalciferol and 25(OH)D3 increased after UVB irradiation of 3 different anatomic sites in the same individuals.
• UVB exposure of a larger skin area resulted in greater increases in serum cholecalciferol concentrations.
• Sporadic exposure of only face and hands was capable of a significant rise in serum concentrations of 25(OH)D3.

BackgroundCholecalciferol is an essential steroid produced in the skin by solar ultraviolet B radiation (UVB 290–315 nm). Skin production of cholecalciferol depends on factors affecting UVB flux, age and exposed skin area.PurposeSerum cholecalciferol and 25-hydroxyvitamin D3 [25(OH)D3] concentrations were measured after UVB irradiation of 3 different skin areas to compare the skin capacity to produce vitamin D in different anatomic sites in the same individuals.MethodTen voluntary Caucasians (skin photo type II & III, aged 48 ± 12 years (±SD)) were exposed to broadband UVB (280–320 nm) between February and April. Hands and face, upper body and whole body were exposed to a suberythemic dose of UVB (median 101 mJ/cm2 (min 66, max 143)) (for 3 subsequent days 24 h apart with a wash out period of about 3 weeks (median 18 days (min 11, max 25)) between the exposures of respective area. Serum concentrations of cholecalciferol and 25(OH)D3, were measured immediately before the first and 24 h after the last dose of radiation.ResultsThere was a significantly higher increase in serum cholecalciferol after UVB exposure of the two larger skin areas compared to face and hands, but no difference in increase was found between upper body and whole body exposures.ConclusionExposure of a larger skin area was superior to small areas and gave greater increase in both serum cholecalciferol and serum 25(OH)D3 concentrations. However, exposure of face and hands, i.e. only 5% of the body surface area, was capable of increasing serum concentrations of 25(OH)D3.