Megavitamin therapy

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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. Megavitamin therapy is typically used in alternative medicine by practitioners who call their approach orthomolecular medicine.^[1] Vitamins are useful in preventing and treating illnesses specifically associated with dietary vitamin shortfalls, 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.^[2][3] It is generally accepted that doses of any vitamin greatly in excess of nutritional requirements will result either in toxicity (vitamins A and D) or in the excess simply being metabolised; thus evidence in favour of vitamin supplementation supports only doses in the normal range.^[4][5][6] Critics have described some aspects of orthomolecular medicine as food faddism or even quackery.^[7][8][9] Research on nutrient supplementation in general suggests that some nutritional supplements might be beneficial, and that others might be harmful;^[10][11][12] several specific nutritional therapies are associated with an increased likelihood of the condition they are meant to prevent.^[13]