Is the effect of phototherapy in psoriasis partly due to an impact on vitamin D metabolism?

Abstract

To elucidate the effect of phototherapy on vitamin D metabolism in psoriatics, the serum concentrations of the major vitamin D metabolites (25-hydroxy-vitamin D (25(OH)D), 1,25-dihydroxy-vitamin D (1,25(OH)2D), and 24,25-dihydroxy-vitamin D (24,25(OH)2D)) were studied in 10 patients with disseminated psoriasis, both before and after phototherapy. Some 3-4 weeks of Goeckerman therapy induced significantly increased serum levels of 25(OH)D (mean: 24.6 ng/ml versus 54.4 ng/ml; (p less than 0.001] and 24,25(OH)2D (mean: 2.01 ng/ml versus 3.49 ng/ml; (p less than 0.001)). After phototherapy the mean serum level of 1,25(OH)2D increased nearly to the level found in healthy controls (mean: 23.8 vs. 32.2 pg/ml). However, this increase was not significant. It is shown that conventional phototherapy does have an impact on vitamin D metabolism in psoriatics. Since previous investigations have indicated an abnormal vitamin D metabolism in patients with psoriasis, it is possible that the beneficial effect of phototherapy in this disease might be due partly to an impact on vitamin D metabolism.