The importance of vitamin D levels in autoimmune diseases.

In addition to its role in calcium homeostasis, it is believed that the active form of vitamin D has immunomodulatory effects on cells of the immune system, particularly T lymphocytes, as well as on the production and action of several cytokines. The interaction of vitamin D with the immune system has been the target of a growing number of publications in recent years. Current studies have linked the deficiency of vitamin D with different autoimmune diseases, including insulin-dependent diabetes mellitus (IDDM), multiple sclerosis (MS), inflammatory bowel disease (IBD), systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA). This article reviews the physiology and immunomodulatory role of vitamin D, emphasizing its involvement in rheumatic diseases such as SLE and RA.