Serum 25-OH vitamin D concentrations are linked with various clinical aspects in patients with systemic sclerosis: a retrospective cohort study and review of the literature.

Low vitamin D serum concentrations have been reported in several autoimmune conditions. The study's aim was to explore such a relationship in a large multinational population of patients with systemic sclerosis (SSc) and to pursue possible clinical and laboratory correlates with vitamin D concentrations. 327 sera samples of European patients with SSc and 141 samples of compatible healthy controls were studied for vitamin D concentrations using the commercial kit LIAISON 25-OH vitamin D assay (Diasorin). Additionally, clinical parameters including the Rodnan skin score, diffusing lung capacity for carbon monoxide (DLCO), systolic pulmonary artery pressure (sPAP), forced vital capacity (FVC), and nailfold video capillaroscopic, erythrocyte sedimentation rate (ESR), anti-nuclear antibodies (ANA and scl70), rheumatoid factor (RF) were investigated. Vitamin D serum concentration was 13.5 ± 9.0 ng/ml (mean ± standard deviation) in patients with SSc compared to 21.6 ± 9.7 ng/ml in a control group (p<0.001). A negative correlation between patients' age and vitamin D concentration (r = -0.2, p<0.05, n = 96) was observed. An inverse relationship was found between skin involvement and vitamin D serum concentrations; Patients with a Rodnan skin score of 10 or lower (n = 11) had a mean vitamin D concentration of 17.7 ± 10.4 ng/ml compared to patients with a score above 10 (n = 28) 8 ± 10.1 ng/ml (p=0.02, by the Mann-Whitney test). In conclusion, Patients with SSc have significantly lower serum vitamin D concentrations compared to healthy controls; moreover fibrosis of the cutaneous tissue is inversely related to the vitamin D concentration.