Vitamin D - Vitamins

Vitamin D

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 .

Vitamin D and the Elderly.     Food and sunlight are primary sources of vitamin D, and because many elderly people do not get enough of either one, they are often vitamin D-deficient. Older people also manufacture vitamin D more slowly, and the resulting deficiency can cause their bones to weaken and grow brittle. As a result, researchers have urged that the RDA for vitamin D be raised for this age group. Some preliminary findings suggest that taking vitamin D supplements may delay bone mass loss.

The importance of vitamin D in the bone formation of infants and bone preservation in the elderly is directly related to its role in controlling the body's ability to absorb phosphorous and calcium. Apparently, the human requirement for calcium changes dramatically throughout the life cycle. The need for calcium rises during growth in childhood, pregnancy, lactation, and menopause, and is lower between the ages of 25 and 51–thus the daily dietary requirement ranges from 5–10 mcg.

Vitamin D Supplements.     Dihydrotachysterol, a form of vitamin D, is used to treat hypoglycemia, which occurs when there is insufficient calcium in the blood or when calcium is not used properly by the body. Calcitrol, another form of vitamin D available only by prescription, is used to treat hypoglycemia and certain types of bone disease that occur in patients who are undergoing renal dialysis for kidney disease. A third form of vitamin D, calciportiol, has been shown to be an effective topical treatment for psoriasis, according to L. May in Drug Information , published in 1993.