Vitamin D is a fat-soluble vitamin.
Our bodies can manufacture it when our skin is exposed to sunlight. The most important thing vitamin D does is to maintain blood levels of calcium within normal limits. It does this by regulating the way the intestines absorb calcium and phosphorus from food. Without vitamin D, a deficiency of dietary calcium will cause the body to rob the bones of calcium to maintain appropriate calcium blood levels. Vitamin D also may reduce the risk of colon cancer, breast cancer and arthritis.