Vitamin D and Autoimmune Thyroid Diseases - a Review

The essential biological action of vitamin D is regulation of calcium and phosphorus metabolism and preserving bone health. In recent years there have been reports about the extraskeletal actions of vitamin D and its role in the regulation of immune system. Vitamin D supplementation appears to reduce the incidence of cardiovascular diseases, cancer, and infections and be able to reduce all-cause mortality. Deficiency of vitamin D has been found to correlate with the increased incidence of autoimmune diseases, including type 1 diabetes mellitus, rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis. Autoimmune thyroid diseases (AITD), including Graves' disease, Hashimoto's thyroiditis are relatively common autoimmune disorders affecting more than 5% of general population. It has been shown that vitamin D receptors (VDR) and 1-alpha hydroxylase are expressed in papillary thyroid cancer and normal thyroid tissue, suggesting local synthesis of 1,25(OH)2D in the thyroid. While VDR gene polymorphism has been found in much research to be associated with AITDs, very few studies have examined the impact of vitamin D deficiency on the incidence of AITDs in humans with conflicting results. This review focuses on the association between vitamin D and autoimmune thyroid diseases and summarizes the results of vitamin D supplementation studies in patients with AITD.