The endocrine vitamin D system in the gut

The active vitamin D metabolite 1 alpha,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3) has important regulatory actions in the gut through endocrine and probably also intracrine, autocrine and paracrine mechanisms. By activating the vitamin D receptor (VDR), which is expressed at a high level in the small intestine and colon, 1,25(OH)(2)D-3 regulates numerous genes that control gut physiology and homeostasis. 1,25(OH)(2)D-3 is a major responsible for epithelial barrier function and calcium and phosphate absorption, and the host's defense against pathogens and the inflammatory response by several types of secretory and immune cells. Moreover, recent data suggest that 1,25(OH)(2)D-3 has a regulatory effect on the gut microbiota and stromal fibroblasts. Many studies have linked vitamin D deficiency to inflammatory bowel diseases (ulcerative colitis and Crohn's disease) and to an increased risk of colorectal cancer, and the possible use of VDR agonists to prevent or treat these diseases is receiving increasing interest. (C) 2016 Elsevier Ireland Ltd. All rights reserved.