Vitamin D is a fat-soluble vitamin chemically related to steroids. It is essential for the normal formation of bones and teeth and for the absorption of calcium and phosphorus in the gastrointestinal tract. Vitamin D is also called cholecalciferol and is available from both natural and synthetic sources.
Small amounts of vitamin D are present in natural foods, especially milk and dairy products. Other natural foods containing vitamin D include saltwater fish, especially salmon, sardines, and herring; organ meats; fish-liver oils; and egg yolks. Vitamin D is also obtained through exposure to sunlight. Ultraviolet rays activate a form of cholesterol in an oil of the skin and convert it to a type of vitamin D, which is then absorbed. In some cases, vitamin D cannot be absorbed without the presence of other foods such as fat.
Ten micrograms per day, or 400 International Units (IU), is the recommended amount of vitamin D to ensure normal development in babies. When a normal diet does not supply sufficient vitamin D, supplements are often recommended.
Vitamin D deficiency can result in osteoporosis and osteodystrophy. Lack of vitamin D may also lead to rickets, especially in children, weakening bones and teeth. In adults, a vitamin D deficiency may cause osteomalacia, in which calcium is lost from bones, causing chronic pain in the ribs, lower spine, pelvis, and legs.
Like vitamin A, vitamin D can accumulate in the body, causing such serious side effects as kidney failure and kidney stones. Symptoms that indicate a person has consumed too much vitamin D include nausea, weakness, and widespread aches, usually followed by more serious problems, such as high blood pressure and irregular heartbeat.
Vitamin D and Disease Prevention
Vitamin D analogs may offer a potential endocrine therapy for breast cancer. In a study reported in the September 23, 1991, issue of Cancer Weekly, patients with advanced breast cancer were treated daily with one gram of calcitrol ointment for six weeks; 21% subsequently showed partial slowing of the spread of cancer. Several other studies have shown that colon cancer is less common in people who have high levels of vitamin D in their blood. One study, conducted over a 19-year period, reported that a daily intake of more than 3.75 micrograms of vitamin D reduced the incidence of colon cancer by 50%. A daily intake of at least 1,200 mg of calcium was reported to reduce the risk of colon cancer by 75%. Based on the results of these studies, daily intakes of 1,500 mg of calcium for women and 1,800 mg of calcium for men, as well as at least 5 mcg of vitamin D, are recommended to reduce the risk of colon cancer, according to an article by Frank Garland in the July 1991 American Journal of Clinical Nutrition.
