Why High Vitamin D Prescriptions?

Vitamin D, which is actually a steroid hormone, is found in fish, eggs and fortified foods. It can also be made by the skin upon exposure to ultraviolet radiation. Early in the 20th century, scientists discovered vitamin D's usefulness in treating rickets, a bone disorder. In subsequent decades, researchers discovered other uses for the "sunshine vitamin," some of which require the administration of very high doses under the supervision of a physician.

Vitamin D Basics

Vitamin D has two forms: ergocalciferol, or D-2, which is synthesized by plants, and cholecalciferol, or D-3, which is synthesized by the human body. Vitamin D regulates the balance of calcium and phosphorus in the body and helps maintain strong bones. According to MayoClinic.com, this nutrient may offer protection against cancer and certain autoimmune diseases. The recommended dietary allowance or RDA is 600 IU for persons between the ages of 1 and 70. Persons older than 70 need 800 IU.

Cautions

Regarding vitamin D safety, MayoClinic.com experts advise people with liver disease to be especially careful with this supplement because it is metabolized by the liver. People taking medication for diabetes should also exercise caution because a vitamin D supplement lowers blood sugar levels. Perhaps the most serious side effect of too much vitamin D is hypercalcemia, a potentially life-threatening condition caused by too much calcium in the bloodstream. Because of the possible risk, anyone taking more than the RDA for this nutrient should consult a physician.

Gastric Bypass Surgery

Even though high doses of vitamin D are usually contraindicated, there are some conditions that call for high doses of this nutrient. As reported in a May 18, 2011, article in "Journal of Obesity," a woman who had undergone a gastric bypass five years earlier developed a severe vitamin D deficiency, probably due to problems with absorption caused by the surgery. She was prescribed 16,000 IU per day, a dose that is more than twice the RDA.

Cancer

A review paper published on July 15, 2010, in the "Journal of Cancer" reports on the beneficial effects of vitamin D for cancer patients. This supplement increases the death of cancer cells, disrupts their life cycle and inhibits their ability to invade normal cells. Vitamin D also increases the effectiveness of many common chemotherapy drugs, gamma radiation and certain antioxidants. Current research indicates that high but intermittent doses of vitamin D are safe and well tolerated by cancer patients. The authors caution, however, that further research using well-designed clinical trials is necessary.

Kidney Transplant

Vitamin D deficiency is common among persons with kidney disease and transplant patients. A study published in the October 2010 issue of "Transplantation Proceedings" found that of 110 transplant recipients, only four had fully normal vitamin D levels. The others had either insufficient or deficient levels. To treat this condition, subjects were given an average of 1,150 IU of vitamin D per day, an amount that exceeds the RDA of 800 IU for older patients by over 40 percent. In these patients, this dose did not lead to hypercalcemia or other side effects.