How 'safe' are antioxidant vitamins?

Interest in a putative disease-preventive role for the so-called antioxidant nutrients derives from a large body of evidence suggesting that oxidative damage is a contributing cause of many life-shortening diseases. Since their use is an otherwise healthy population, it is important that such agents be virtually free of toxicity. The agents of most interest are alpha-tocopherol (vitamin E), ascorbic acid (vitamin C) and beta-carotene. When used for disease prevention, the doses given are several-fold greater the Recommended Dietary Allowance (RDA), the latter being based on amounts necessary for the prevention of classic deficiency conditions recognised decades ago. alpha-Tocopherol, ascorbic acid and beta-carotene are remarkably well tolerated and free from toxicity. Consequently, they are well suited for testing as preventive agents, since their use does not require any toxicity monitoring except in unusual circumstances. An example of the latter would be in patients who are vitamin K deficient, perhaps through anticoagulation with drugs such as warfarin, in which case use of high doses of alpha-tocopherol may increase the bleeding tendency.