Vitamin D, a fat-soluble vitamin that has properties of both a vitamin and a hormone, is required for the absorption and utilization of calcium and phosphorus. It is necessary for growth, and is especially important for the normal growth and teeth in children. It protects against muscle weakness and is involved in regulation of the heartbeat. It is also important in the prevention and treatment of breast and colon cancer, osteoarthritis, osteoporosis, and hypocalcemia; enhances immunity; and is necessary for thyroid function and normal blood clotting.
There are several forms of vitamin, including vitaminD2 (ergocalciferol), which comes from food sources; vitaminD3 (cholecalciferol) which is synthesized in the skin in response to exposure to the sun’s ultraviolet rays; and a synthetic form identified as vitamin D5 (sometimes also D2), of the three, vitamin D3 is considered the natural form of vitamin D and was thought to be the most active. Newer data shows that D2 is as effective as D3 in maintaining vitamin D levels in the blood.
The form of vitamin D that we get from food or supplements is not fully active. It requires conversion by the liver, and then by the kidneys, before it becomes fully active. This is why people with liver or kidney disorders are at a higher risk for osteoporosis. When the skin is exposed to the sun’s ultraviolet rays, a cholesterol compound is the skin is transformed into a precursor of vitamin D. Exposing the face and arms to the sun for fifteen minutes three times a week is an effective way ensure adequate amounts of vitamin D in the body,
Vitamin D has been the ignored vitamin until recently. Studies have shown that at least 40 percent of the people have less-than-optimal levels of vitamin D in their blood. As much as 70 to 80 percent of Hispanic-Americans and African-Americans may be deficient in vitamin D. Those with more coloring in the skin have a harder time absorbing vitamin D from sunlight. In addition, those who live above the 37th latitude obtain virtually no vitamin D from sunlight between November and March.
Not getting enough vitamin D in the diet or from direct sunlight has been linked to the development of several diseases including heart disease, osteoporosis, diabetes, and cancers such as breast and colon. As baby boomers age, the risk of osteoporosis increases. Taking more than 400IU of vitamin D has been shown to reduce the risk of fractures by 20 percent in those over sixty-five years of age. But how much is needed to optimize health is still open for debate.
Cod liver oil, fatty saltwater fish (especially mackerel), dairy products and eggs all contain vitamin D. It is also found in butter, dandelion greens, egg yolks, Cod, halibut, liver, shiitake and chanterelle mushrooms, oatmeal, oysters, salmon, sardines, sweet potatoes, tuna, and vegetable oils. Herbs that contain vitamin D include alfalfa, nettle and parsley.
Vitamin D is also formed by the body in response to the action of sunlight on the skin. Of all the nutrients, this is one of a few that is difficult to reach, the DRI from food alone and supplementation may be needed. It may make sense to take serial blood tests each year with a physical examination to see if you are getting enough vitamin D to maintain healthy levels.