Cutaneous vitamin D3 formation in progressive systemic sclerosis

Progressive systemic sclerosis (PSS) is a predominantly dermal disorder which may be associated with epidermal atrophy. We investigated epidermal function in 8 patients with PSS and their healthy controls matched for age, sex and racial group. We measured the vitamin D3 photosynthetic response to whole body irradiation with ultraviolet light B (UVB). There were no significant differences in basal serum vitamin D3 levels (mean ± SEM: PSS 1.2 ± 0.2 ng/ml; controls 0.8 ± 0.1 ng/ml; p > 0.1) or post UVB blood values (PSS 5.2 ± 1.4 ng/ml; controls 6.9 ± 1.1 ng/ml; p > 0.1); although the increases post-UVB were significant in both groups (p < 0.01). In an additional group of 19 patients with PSS and their corresponding matched healthy controls, we performed determination of random levels of the active vitamin D metabolites, 25-hydroxyvitamin D (25-OH-D) and 1,25-dihydroxyvitamin D [1,25-(OH)2-D]. Similar levels were observed in both groups: 25-OH-D PSS 28 ± 3 ng/ml, controls 29 ± 3 ng/ml; 1,25-(OH)2-D PSS 27 ± 2 pg/ml, controls 31 ± 2 pg/ml (p > 0.1). None of the correlations between skin area involved and vitamin D3 formation or active circulating metabolites reached statistical significance (p > 0.1). We conclude that global epidermal synthesis of vitamin D is retained in PSS and, that the hepatic and renal vitamin D hydroxylating mechanisms function normally in that condition.