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 One patient with photo aggravated psoriasis was withdrawn from the study.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 51 [rather than 59, as given in the originally published article] (32-112) ng/mL at the end of NB–UV-B treatment compared with no change in the control group [corrected]. 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.