(4) Vitamin D manages calcium in blood, bones and gut and helps cells all over body to communicate properly. Vitamin D mainly comes from skin when it is exposed to sunlight. After that, body goes through a number of chemical processes to change it so that body can use it. Vitamin D is actually a hormone rather than a vitamin. The body makes most of the vitamin D it needs; only about 10%comes from our food. The action of sunlight on our skin produces a substance called cholecalciferol, which is converted by the liver to calcidiol. The biologically active form of vitamin D, Calcitriol is produced in kidney. Calcitriol action is similar to steroid hormones.