Introduction : Narrow band UVB (311-313 nm) is commonly used in the treatment of many skin diseases, including psoriasis vulgaris. Under skin exposure to UVB synthesis of vitamin D occurs.

Aim : The aim of the study was to assess the serum concentration of vitamin D in psoriasis vulgaris as well as the changes in 25-hydroxycholecalciferol (25(OH)D) and parathormone (PTH) serum level under a series of UVB exposures. Additionally, we checked the correlation between the final vitamin D concentration and cumulative NB-UVB dose.

Material and methods : The study group included 47 patients with psoriasis vulgaris in the age range 20-65 years old. The patients were treated with 20 NB-UVB exposures. In each patient, 25(OH)D (RIA – radioimmunoassay) and PTH (immunochemiluminescence assay) serum concentration was checked 3 times: before therapy, and after 10 and 20 exposures.

Results : Baseline vitamin D concentration was 26.5 ng/ml. After the first 10 NB-UVB exposures vitamin D serum concentration statistically increased to the value of 38 ng/ml (p < 0.001), and after the next 10 irradiations 25(OH)D level increased (43 ng/ml), although it did not significantly differ compared to the second measurement (p > 0.05). A PTH serum concentration did not statistically change during the whole therapy. A positive correlation between the cumulative NB-UVB dose and the final 25(OH)D serum concentration was observed (p < 0.05).

Conclusions : Deficiency of vitamin D serum level is observed in psoriatic patients. NB-UVB significantly increases 25(OH)D synthesis dependently on cumulative dose, with no effect on PTH serum level. The lower increase in the vitamin D level in the course of phototherapy testifies to the photoadaptation phenomenon.