Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals and chain reactions that may damage the cells of organisms. Antioxidants such as thiols or ascorbic acid (vitamin C) may act to inhibit these reactions. To balance oxidative stress, plants and animals maintain complex systems of overlapping antioxidants, such as glutathione.

The only dietary antioxidants are vitamins A, C, and E. The term antioxidant is also used for industrial chemicals added during manufacturing to prevent oxidation in synthetic rubber, plastics, and fuels, or as preservatives in food and cosmetics.

Dietary supplements marketed as antioxidants have not been shown to improve health or prevent disease in humans. Supplements of beta-carotene, vitamin A, and vitamin E have no positive effect on mortality rate or cancer risk. Additionally, supplementation with selenium or vitamin E does not reduce the risk of cardiovascular disease.

 

Note:   The above text is excerpted from the Wikipedia article Antioxidant, which has been released under the GNU Free Documentation License.