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Many people take large doses of antioxidant vitamin pills, even though there is little evidence that large doses of antioxidant pills prevent disease, and there is some evidence that they may cause disease.

Does it bother you that taking large doses of beta carotene, which is vitamin A, increases risk for heart attacks in men and increase risk for lung cancer in smokers? Does it bother you that large doses of vitamin C do not prevent colon cancer, and do not prolong life in people with cancer? Other studies show that large doses of vitamin E do not prevent lung cancer, heart disease or stroke, or that large doses of selenium do not prevent cancer.

Last year, Barry Haliwell of the National University of Singapore wrote an article in the British medical journal, Lancet, explaining why large doses of antioxidant vitamins sometimes prevent cancer and sometimes cause it. Every chemical reaction in the body releases chemicals called free radicals that damage tissue, which releases certain metals into the cell fluid. Antioxidants convert these free metals, which are harmless, to powerful oxidants that cause further cell damage. So sometimes antioxidants protect cells and other times, they damage them. For example, paraquat is a powerful cancer-causing chemical. If you give vitamin C to animals before giving them paraquat, the vitamin C prevents cells damage and helps protect them from cancer, but if you give these same animals vitamin C after they take paraquat, the vitamin C spreads the cancer. The paraquat causes cells to release large amounts of minerals and the vitamin C then causes these minerals to damage cells and spread the cancer. For this reason and others, the American Cancer Society advises patients not to take large doses of vitamins A, E, C and selenium.

Another reason not to take large doses of antioxidant vitamins is that free radicals kill cancer cells. Rapidly multiplying cancer cells take up antioxidants and use them to protect the cancer cells from being destroyed by oxidants. So antioxidant vitamins can protect preexisting cancer cells from being damaged by oxidants, to spread the cancer. If you think we know all about antioxidants, you do not understand the tremendous controversy going on right now. You should get all the vitamins that you need from the food that you eat. If you want to take recommended dietary allowances of vitamins, go ahead, there is little evidence that you will harm yourself. However when you take large doses of any vitamin, you don't have the foggiest idea whether you are harming yourself and I do not recommend large doses of vitamins to anyone.

Checked 1/7/04

June 1st, 2013
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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