Inflammation and vitamin D

Calcitriol, or 1,25-dihydroxyvitamin D3 is a well-known endocrine regulator of calcium homeostasis. More recently, local calcitriol production by immune cells was shown to exert autocrine or paracrine immunomodulating effects. Immune cells that produce calcitriol also express the vitamin D receptor and the enzymes required to metabolize vitamin D3 (1α-, 25- and 24-hydroxylases). These immunomodulating effects, shown in animal models and cell culture experiments, are both direct and indirect and involve T cells, B cells, and antigen presenting cells (dendritic cells and macrophages), affecting both innate and adaptative immunity. The overall effect is a switch from a Th1/Th17 to a Th2/Treg profile. These immunomodulating properties could explain the epidemiological associations, suggested by observational studies, between vitamin D serum levels and many autoimmune and inflammatory diseases such as rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel diseases, type 1 diabetes, but also infections, cancer, transplant rejection and cardiovascular diseases. Furthermore, vitamin D supplementation showed therapeutic effects in animal models for these diseases. Thus, vitamin D is a key focus for public health efforts and may hold promise for the treatment of dysimmune diseases.