Background: Ultraviolet B (UVB) radiation increases the serum level of 25-hydroxyvitamin D [25(OH)D]. However, the impact of UVA on vitamin D synthesis by UVB is poorly understood clinically.
Objective: To examine how different combinations of UVA and UVB radiation affect S-25(OH)D for the same vitamin D-weighted exposure.
Materials and methods: Healthy participants were recruited and subsequently divided into four comparable groups regarding initial 25(OH)D value. The different radiations given were whole-body UVB (n = 23), UVAB (n = 23) and UVA (n = 10). The controls (n = 19) had no intervention. The exposure times were chosen to give the same calculated vitamin D effective dose (suberythemal exposures ≤1 standard erythema dose). Blood samples were collected before the first irradiation (t0), immediately after the last (fifth) irradiation (t1) and then after another 2 days after the last (fifth) irradiation (t2).
Results: UVB and UVAB radiation significantly increased 25(OH)D levels. In the UVA group the increase was less with the same vitamin D-weighted radiation dose.
Conclusions: Short sessions of UVB or UVAB radiation with the same vitamin D-weighted exposure increased 25(OH)D levels. The UVA dose does not influence 25(OH)D levels under short exposure times. However, there was a significantly lower increase of 25(OH)D levels during longer UVA irradiation (≥9 min).
Keywords: 25(OH)D; UVA; UVB; sunbeds; vitamin D.
© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.