Vitamin D and autoimmunity: what happens in autoimmune polyendocrine syndromes?

Purpose To evaluate the Vitamin D status of patients with a single autoimmune disease and of patients with several autoimmune diseases. Methods We enrolled 35 patients with isolated type 1 diabetes mellitus (T1DM), 60 with autoimmune polyendocrine syndromes (APS) including T1DM and 72 control subjects. Among patients with APS, 10 were classified as type 2 (Addison's disease + T1DM), whereas the other 50 as type 3 (autoimmune thyroid disease + T1DM + other autoimmune diseases). Vitamin D (25-OHD) levels were assessed by a chemiluminescent immunoassay in all patients and controls on samples drawn in the morning of the same months. Results Both groups of APS and T1DM patients showed 25-OHD levels significantly lower than healthy controls (p < 0.001 for both vs controls), without any significant difference between the two groups (p = 0.80). The highest prevalence of vitamin D deficiency (values < 20 ng/ml) was observed in APS type 3 subgroup (8 out of 50 patients, 16 %). Conclusions Patients with APS present reduced vitamin D circulating levels, but the vitamin D status is not different between patients with single or multiple autoimmune diseases. The kind of autoimmune disease, rather than the association of several autoimmune diseases, may influence negatively the levels of vitamin D. Further prospective studies are needed to clarify if impaired vitamin D level is a causal factor in the pathogenesis of autoimmune diseases or a consequence of them.