Background: Vitamin D insufficiency is common in winter in the Nordic countries.
Objectives: To examine whether a short course of narrowband ultraviolet B (NB-UVB) improves vitamin D balance.
Methods: Fifty-six healthy, white women (mean age 41 years) volunteered and 53 completed the study. NB-UVB exposures were given on seven consecutive days either on the whole body (n = 19), on the head and arms (n = 9) or on the abdomen (n = 14). Similarly, seven solar simulator exposures were given on the face and arms (n = 11). The cumulative UVB dose was 13 standard erythema doses in all regimens. Serum calcidiol (25-hydroxyvitamin D) concentration was measured by radioimmunoassay before and after the NB-UVB exposures. Follow-up samples were taken from the whole-body NB-UVB group at 2 months.
Results: At onset 41 women (77%) had vitamin D insufficiency (calcidiol < 50 nmol L(-1)) and six (11%) had vitamin D deficiency (calcidiol < 25 nmol L(-1)). Calcidiol concentration increased significantly, by a mean of 11.4 nmol L(-1) when NB-UVB was given on the whole body, by 11.0 nmol L(-1) when given on the head and arms and by 4.0 nmol L(-1) when given on the abdomen. Solar simulator exposures given on the face and arms increased calcidiol by 3.8 nmol L(-1). After 2 months serum calcidiol was still higher than initially in the group who received NB-UVB exposures on the whole body.
Conclusions: NB-UVB exposures given on seven consecutive days on different skin areas of healthy women significantly improved serum calcidiol concentration. A short low-dose NB-UVB course can improve vitamin D balance in winter.