Vitamin D and ultraviolet phototherapy in Caucasians
•The relationship between UV dose and 25(OH)D increase was analyzed in 18 studies.•The UV dose–response curve for 25(OH)D increase is not linear and reaches a plateau.•The increments of serum 25(OH)D decrease with increasing its baseline level.•One month course with total UVB dose of 23 SEDs restores summer 25(OH)D values.
Ultraviolet B (UVB) radiation increases vitamin D level, but the influence of different UV sources (broadband and narrowband UVB lamps, solar simulators and sunbeds) and exposure durations have not been well characterized. In this study the influence of different UV sources on serum 25-hydroxyvitamin-D3 (25(OH)D3) levels in humans are reviewed. Serum 25(OH)D levels before and after UV exposure, and UV doses were extracted from 18 papers published in the past eight years. It was found that the UV dose–response curve for vitamin D generation in humans, as measured by the increments of serum 25(OH)D, is not linear with increasing UV doses and reaches a plateau at about 55 nmol/L after 4–5 weeks. About a half of this increase is equal to the difference between winter and summer 25(OH)D levels, and may be reached after 23 SEDs. The increments decrease with increasing baseline concentration of serum 25(OH)D, and the efficiency of only 0.7 nmol/L per SED is expected on the average when initial concentrations are higher than 50–60 nmol/L. A whole body exposure to 2 SEDs of UVB radiation 3 times per week is expected to rise serum 25(OH)D with an initial rate of 3.9 nmol/L per SED, bringing a winter level of serum 25(OH)D up to a summer level.
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 147, June 2015, Pages 69–74