The Effect of Narrow-Band Ultraviolet B Phototherapy on Free and Total Vitamin D Serum Levels in Mild to Severe Plaque Psoriasis.

Vitamin D plays an important role in skin inflammation in psoriasis. The beneficial effects of ultraviolet light B (UVB) phototherapy in psoriasis are partly attributed to UVB-induced increase of vitamin D levels. In clinical practice, total 25-hydroxy vitamin D (25(OH)D) levels are measured to assess sufficiency, but it might be more accurate to measure free 25(OH)D levels. The aim of this study was to measure free serum 25(OH)D levels in psoriasis patients before and after phototherapy and to investigate if free 25(OH)D correlates stronger to disease severity than total 25(OH)D. Twenty adults (>18 years) with psoriasis were included for treatment with narrow-band UVB (NB-UVB) phototherapy for 10-12 weeks. Psoriasis Area and Severity Index (PASI) and Visual Analogue Scale (VAS) were used to assess disease severity. Serum levels of total 25(OH)D, free 25(OH)D, and 1,25(OH)D were measured before and after NB-UVB. Total 25(OH)D, free 25(OH)D, 1,25(OH)D and the percentage of free 25(OH)D increased after NB-UVB, and PASI and VAS improved. The increase in total and free 25(OH)D remained significant when stratifying for vitamin D confounders. No correlations between disease severity and vitamin D levels were found. Total and free 25(OH)D levels were positively correlated before and after NB-UVB. NB-UVB is an effective treatment for mild to severe plaque psoriasis and increases not only total but also free 25(OH)D levels, as well as the percentage of free 25(OH)D, suggesting an increased bioavailability of skin-produced vitamin D.