Chapter 25 - Vitamin D

Abstract

Autoimmune diseases (AIDs) are triggered by a multitude of factors, and vitamin D is a hormone that might be involved in their development. Vitamin D acts in target tissues through signaling by an intranuclear receptor termed vitamin D receptor (VDR). The identification of VDRs in all cells of the immune system and the discovery that dendritic cells can produce the metabolically active form of vitamin D have led to the notion that vitamin D could act as an immunomodulator. In fact, vitamin D has been shown to be actively involved in the regulation of innate and adaptive immune responses. In this sense, vitamin D has been documented to be involved in several autoimmune disorders and its deficiency has been associated with the pathogenesis and severity of multiple sclerosis, type 1 diabetes mellitus, rheumatoid arthritis, systemic sclerosis, and systemic lupus erythematosus, among others. Nevertheless, low levels of vitamin D have often been reported in patients with different AIDs, although it is still unclear if this finding is a cause or consequence of the disease.Regarding vitamin D supplementation in AIDs, most of the published studies have been inconclusive. However, this fact may be linked to measuring the metabolite 25(OH)D instead of the active form calcitriol.