Serum vitamin D3 levels in patients with psoriasis and control subjects matched for age, sex, racial group, and UV-B irradiance. Blood was obtained 1 hour before, and 24 hours after ex¬ posure to UV-B in a photounit. Vitamin D3 concentration in¬ creased markedly following UV-B treatment. Both basal and post-UV-B levels are similar in control subjects and in patients with psoriasis. Vitamin D2 was not detected in any of the blood samples. surface. One patient had no active lesions. None of the individuals had received any treatment for the psoriasis for at least 2 months preceding the study. All had normal hepatic and renal function; none was taking vitamin D, anticonvulsant medications, or corticosteroids. Control subjects were healthy individuals matched by age (mean age, 36 years; range, 24 to 73 years), sex, and racial group.All subjects were exposed to a single dose of UV-B irradiation (UVR), delivered in a walk-in phototherapy unit. In seven patients and their controls, the UV-B dose was 24 mj/cm2, and in the remaining four psoriatic individuals and corresponding control subjects, the UV-B dose was 21 mj/cm2. In the same photounit the minimal erythema dose for whites ranges from 33 to 36 mJ/cm2. Blood samples were obtained twice, 1 hour before UV-B (basal de¬ termination) and 24 hours after UV-B irradiance, and analyzed as previously reported.2The significance of differences was evaluated by the Student t test.Results.-As seen in the Figure, basal vitamin D3 levels of psoriatic patients were similar to matched control sub¬ jects (2.78 ± 1.06 vs 3.53 ± 0.93 nmol/L, mean ± SEM; P > .1). Following UV-B irradiance, patients with psoriasis exhibited slight blunting of the vitamin D3 synthetic re¬ sponse, although the difference with control subjects was not significant (15.15 ± 3.61 vs 20.66 ± 2.54 nmol/L; P > .1). Compared with basal, the serum vitamin D3 in¬ creases were highly significant in both groups (P < .01).Levels of serum 25-OH-D were similar in patients with psoriasis and in control subjects (55.4 ± 7.5 vs 65.6 ± 8.0 nmol/L; P > .1); as were serum l,25-(OH)2-D (81.2 ± 10.8 vs 70.4 ± 5.8 pmol/L; P> .1) and vitamin D binding protein levels (6.16 ± 0.55 vs 5.72 ± 0.59 nmol/L; P > .1). The nor¬ mal range for 25-OH-D is 22.5 to 130 nmol/L; for 1,25-(OH)2-D, 72.1 to 180.3 pmol/L; and, for vitamin D binding protein, 4.83 to 6.89 nmol/L. Comment.-The present results indicate that UV-Bstimulated vitamin~D , synthesis is unimpaired in psoriatic individuals. Furthermore, the serum levels of the vitamin D metabolites 25-OH-D and l,25-(OH)2-D and of the hepatic vitamin D binding protein are similar in patients with pso¬ riasis and their appropriately matched controls, and well within the normal reference range. Nevertheless, adminis¬ tration of l,25-(OH)2-D is reportedly effective in psoriasis, although this action has been ascribed to its potent antiproliferative activity (in fibroblasts),4 and its stimulation of terminal differentiation in cultured keratinocytes.5 The beneficial effect of l,25-(OH)2-D would resul...