Vitamin D levels depend on many variables, including sun exposure, age, ethnicity, body mass index, use of medications and supplements. A much higher oral vitamin D intake than the current guidelines is necessary to maintain adequate circulating 25(OH)D levels in the absence of UVB radiation of the skin. In addition to the traditional known metabolic activities, vitamin D has been shown to modulate the immune system, and its deficiency has been linked to the development of several autoimmune disorders including type 1 diabetes and multiple sclerosis. Experimental use of vitamin D has revealed a novel role in the immunopathogenesis of autoimmune diseases. Disorders such as systemic lupus erythematosus, rheumatoid arthritis, Behçet's, polymyositis/dermatomyositis and systemic scleroderma have all been associated to some extent to vitamin D deficiency. If vitamin D deficiency occurs at a higher rate in patients with autoimmune disorders, then appropriate supplementation may be indicated.
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