The Effect of Narrowband UV-B Treatment for Psoriasis on Vitamin D Status During Wintertime in Ireland

Objectives: To determine whether narrowband UV-B (NB UV-B) may mediate its beneficial effect on psoriasis by increasing vitamin D levels, and to assess the effect of NB UV-B on vitamin D status in patients with psoriasis in wintertime. Design: A prospective controlled study from October 2008 to February 2009. Setting: A dermatology outpatient department at a university teaching hospital. Patients: Thirty consecutive patients with psoriasis treated with NB UV-B and 30 control patients with psoriasis were recruited. Control patients were recruited within 1 week of treated patients to control for seasonal variation of serum 25-hydroxyvitamin D [25(OH)D] levels. One patient with photoaggravated psoriasis was withdrawn from the study. Intervention: Narrowband UV-B was administered 3 times per week. Main Outcome Measure: Serum 25(OH)D was measured at baseline, after 4 weeks and at completion of treatment. Results: Levels of serum 25(OH)D increased significantly (P<.001) from a median (range) of 23 (9-46) ng/mL at baseline to 59 (32-112) ng/mL at the end of NB UV-B treatment compared with no change in the control group. The change in serum 25(OH)D level correlated with the number of exposures of NB UV-B (r=0.61; P<.001) and cumulative UV-B dose (r=0.47; P=.01) but not with treatment response. At the end of the study, all patients in the treatment group were vitamin D sufficient, but 75% of the control group had vitamin D insufficiency [serum 25 (OH)D level <20 ng/mL]. In a multiple regression model, prior phototherapy was the sole predictor of baseline serum 25(OH)D level (r(2)=0.13; P=.006), whereas the number of exposures of NB UV-B predicted change in serum 25(OH) D level (r(2)=0.38; P=.001). Conclusions: Narrowband UV-B effectively increases serum 25(OH)D level while clearing psoriasis. Up to 75% of Irish patients with psoriasis were shown to be vitamin D insufficient during wintertime.