Changes in serum 25-hydroxyvitamin D and cholecalciferol after one whole-body exposure in a commercial tanning bed: a randomized study.

We wanted to evaluate the cutaneous synthesis of 25OHD and cholecalciferol after one whole-body exposure to ultraviolet radiation type B (UVB) in a randomized setup. Healthy volunteers were randomized to one whole-body exposure in a commercial tanning bed with UVB emission (UVB/UVA ratio 1.8-2.0%) or an identical placebo tanning bed without UVB. The output in the 280-320 nm range was 450 µW/cm². Blood samples were analyzed for 25OHD and cholecalciferol at baseline and during 7 days after treatment. We included 20 volunteers, 11 to UVB and 9 to placebo treatment. During the first 6 h, no significant differences in 25OHD between the groups were found. At the end of the study, we found a mean increase of 25OHD in the UVB group of 4.5 nmol/l (SD 7 nmol/l) compared to a decline of -1.2 nmol/l (SD 7 nmol/l) in the placebo group (p = 0.1). A linear mixed model yielded an increase of 25OHD in the UVB group of 1.0 nmol/l per 24 h (p < 0.01). For cholecalciferol, we found a near significant increase of 1 pmol/l per hour in the UVB group compared to the placebo group during the first 6 h (p = 0.052). One tanning bed session had significant, but modest impact on the level of 25OHD during 7 days after exposure to UVB.