Vitamin D Metabolism and Function in the Skin

The keratinocytes in the skin were identified as the primary source of vitamin D for the body and possessed the necessary enzymes to convert vitamin D to its active form, 1,25(OH)(2)D. These cells also expressed the vitamin D receptor (VDR), allowing them to respond to the active metabolite they produced. The active form of vitamin D and its receptor regulated several skin functions, including inhibiting proliferation, stimulating differentiation, forming the permeability barrier, promoting innate immunity, and supporting the hair follicle cycle. The regulation of these actions involved various coregulators such as DRIP, SRC, hairless (Hr), and β-catenin. The review focused on the regulation of vitamin D production and metabolism in the skin and the functions controlled by 1,25(OH)(2)D and its receptor.