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. Studies to investigate these possible benefits of vitamin D are under way.
Most foods have little or no vitamin D, and few foods besides milk are fortified with it.
Actually, our bodies can manufacture vitamin D for us when the skin is exposed to adequate sunlight. To ensure that this important process occurs, you need to expose your hands, face and arms to the sun for 10-15 minutes, two or three times a week, between 8 a.m. and 4 p.m. Using sunscreen during this brief period may interfere with the process. Margarine is fortified with 20 IU per teaspoon. Some fatty fish are sources, but unless you eat them often you will not get enough.