EFFECT OF UVB PHOTOTHERAPY AND ORAL CALCITRIOL (1,25-DIHYDROXYVITAMIN-D-3) ON VITAMIN-D PHOTOSYNTHESIS IN PATIENTS WITH PSORIASIS

Background: Phototherapy and activated forms of vitamin D help clear p soriasis. Objective: The influence of UVB phototherapy and oral calcit riol (1,25-dihydroxyvitamin D-3) On vitamin D photosynthesis was asses sed in 16 patients. Methods: Patients were randomly selected to receiv e orally either placebo or calcitriol (0.5 to 2 mu g daily) for the du ration of the 8-week study; all patients received approximately 21 UVB treatments. Before and after treatment, serum levels of 25-hydroxyvit amin D and calcitriol were measured by high-pressure liquid chromatogr aphy. Results: Although calcitriol had no additive effect on photother apy as a treatment modality, a significant increase in serum 25-hydrox yvitamin D levels occurred in both groups; in three patients extraordi narily high levels developed (>120 ng/ml). Oral calcitriol significant ly increased calcitriol serum levels. Increased serum calcitriol did n ot inhibit cutaneous synthesis of vitamin D or its hepatic conversion to serum 25-hydroxyvitamin D. Conclusion: UVB induces high levels of v itamin D photosynthesis. Because oral or topical calcitriol alone help s clear psoriasis, studies to explore the possible influence of UVB ph ototherapy on its production should be considered. If UVB phototherapy induces cutaneous calcitriol synthesis this could explain the lack of added benefit to treatment when oral calcitriol is administered with phototherapy.