Vitamin D is a group of fat-soluble pro-hormones, the two major forms of which are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol).
Vitamin D performs a wide range of critical functions in the body including helping to maintain normal blood levels of calcium and phosphorus, aiding in the absorption of calcium from food, promoting bone mineralization, and reducing loss of calcium from the body. In addition, vitamin D is necessary for healthy bones and teeth, and may help reduce the risk of many cancers.
Vitamin D is found in food sources including milk, liver, fish oil, tuna, eggs, sardines, salmon. However, it is absorbed and utilized best through regular, moderate exposure to the sun. About 15 minutes per day will give you adequate vitamin D.