Megavitamin therapy is the use of large doses of vitamins, often many times greater than the recommended dietary allowance (RDA) in the attempt to prevent or treat diseases. It is typically used in complementary and alternative medicine by practitioners who call their approach "orthomolecular medicine", but also used in mainstream medicine for "exceedingly rare" genetic conditions that respond to megadoses of vitamins. In 2002, a review of these conditions identified about 50 that respond to "high-dose vitamin therapy". Further understanding of these conditions is expected to play a part in the emerging field of nutrigenomics.
Nutrients may be useful in preventing and treating some illnesses, but the conclusions of medical research are that the broad claims of disease treatment by advocates of megavitamin therapy are unsubstantiated by the available evidence. It is generally accepted that doses of any vitamin greatly in excess of nutritional requirements, will result either in toxicity or in the excess simply being metabolised - evidence in favour of vitamin supplementation supports only doses in the normal range. Critics have described some aspects of orthomolecular medicine as food faddism or even quackery. Research on nutrient supplementation in general suggests that some nutritional supplements might be beneficial, and that others might be harmful; several specific nutritional therapies are associated with an increased likelihood of the condition they are meant to prevent.
Megavitamin therapy must be distinguished from the usual 'vitamin supplementation' approach of traditional multivitamin pills. Megavitamin doses are far higher than the levels of vitamins ordinarily available through western diets. Multivitamin supplementation has been demonstrated to have negligible effect in treating cancer. A study of 161,000 individuals (post-menopausal women) provided, in the words of the authors, "convincing evidence that multivitamin use has little or no influence on the risk of common cancers, cardiovascular disease, or total mortality in postmenopausal women".
In the 1930s and 1940s, some scientific and clinical evidence suggested that there might be beneficial uses of vitamins C, E, and B3 in large doses. Beginning in the 1930s, the Shutes in Canada developed a megadose vitamin E therapy for cardiovascular and circulatory complaints, naming it the "Shute protocol". Tentative experiments in the 1930s with larger doses of vitamin C were superseded by Fred R. Klenner's development of megadose intravenous vitamin C treatments in the 1940s. William Kaufman published articles in the 1940s that detailed his treatment of arthritis with frequent, high doses of niacinamide.
In 1954, R. Altschul and Abram Hoffer applied large doses of the immediate release form of niacin (Vitamin B3) to treat hypercholesterolemia. In a 1956 publication entitled Biochemical Individuality, Roger J. Williams introduced concepts for individualized megavitamins and nutrients. Megavitamin therapies were also publicly advocated by Linus Pauling in the late 1960s. In 1956, experimental results suggested niacin could be useful in the treatment of high cholesterol, results that were confirmed in 1986.
Usage of therapy
An American cottage industry in the late 20th century, evolving megavitamin therapies are integrated with orthomolecular and naturopathic medicine. Although megavitamin therapies still largely remain outside of the structure of evidence-based medicine, they are increasingly used by patients, with or without the approval of their treating physicians.
In 2008, researchers established that higher vitamin C intake reduces serum uric acid levels and may be useful in the prevention of gout.
The proposed efficacy of various megavitamin therapies has been contradicted by results of one clinical trial. A review of clinical trials in the treatment of colds with small and large doses of Vitamin C has established that there is no evidence for its efficacy. After 33 years of research, it is still not established whether vitamin C can be used as a treatment for cancer.
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