antioxidant, substance that prevents or slows the breakdown of another substance by oxygen. Synthetic and natural antioxidants are used to slow the deterioration of gasoline and rubber, and such antioxidants as vitamin C (ascorbic acid), butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA) are added to foods (see food additives) to prevent them from becoming rancid or from discoloring.

In the body, nutrients such as beta-carotene (a vitamin A precursor), vitamin C, vitamin E, and selenium have been found to act as antioxidants. They act by scavenging free radicals, molecules with one or more unpaired electrons, which rapidly react with other molecules, starting chain reactions in a process called oxidation. Free radicals are a normal product of metabolism; the body produces its own antioxidants (e.g., the enzyme superoxide dismutase) to keep them in balance. However, stress, aging, and environmental sources such as polluted air and cigarette smoke can add to the number of free radicals in the body, creating an imbalance. The highly reactive free radicals can damage healthy DNA and have been linked to changes that accompany aging (such as age-related macular degeneration, a leading cause of blindness in older people) and with disease processes that lead to cancer, heart disease, and stroke.

Studies have suggested that the antioxidants that occur naturally in fresh fruits and vegetables have a protective effect. For example, vitamin E and beta-carotene appear to protect cell membranes; vitamin C removes free radicals from inside the cell. There is still some question as to whether antioxidants in the form of dietary supplements counteract the effects of increased numbers of free radicals in the body. Some scientists believe that regular consumption of such supplements interferes with the body's own production of antioxidants.

The Columbia Encyclopedia, 6th ed. Copyright© 2014, The Columbia University Press.

Selected full-text books and articles on this topic

Beyond the 120-Year Diet: How to Double Your Vital Years
Roy L. Walford.
Four Walls Eight Windows, 2000 (Revised edition)
Librarian’s tip: "Antioxidants" begins on p. 170
Controversies in Food and Nutrition
Myrna Chandler Goldstein; Mark A. Goldstein.
Greenwood Press, 2002
Librarian’s tip: Chap. 11 "Antioxidants"
Antioxidant Supplementation Prevents Oxidation and Inflammatory Responses Induced by Sidestream Cigarette Smoke in Old Mice. (Articles)
Zhang, Jin; Jiang, Shuguang; Watson, Ronald R.
Environmental Health Perspectives, Vol. 109, No. 10, October 2001
Association of Blood Arsenic Levels with Increased Reactive Oxidants and Decreased Antioxidant Capacity in a Human Population of Northeastern Taiwan
Wu, Meei-Maan; Chiou, Hung-Yi; Wang, Tsung-Wei; Hsueh, Yu-Mei; Wang, Iuan-Horng; Chen, Chien-Jen; Lee, Te-Chang.
Environmental Health Perspectives, Vol. 109, No. 10, October 2001
Breathe Easy: Antioxidants May Be an Effective and Inexpensive Way to Maintain Healthy Lungs and Lower the Risk of Chronic Disease
Ulrich, Clare.
Human Ecology, Vol. 30, No. 1, March 2002
Rapid Increases in the Steady-State Concentration of Reactive Oxygen Species in the Lungs and Heart after Particulate Air Pollution Inhalation. (Articles)
Gurgueira, Sonia A.; Lawrence, Joy; Coull, Brent; Murthy, G. G. Krishna; Gonzalez-Flecha, Beatriz.
Environmental Health Perspectives, Vol. 110, No. 8, August 2002
Chromium(III)-Induced 8-Hydroxydeoxyguanosine in DNA and Its Reduction by Antioxidants: Comparative Effects of Melatonin, Ascorbate, and Vitamin E
Qi, Wenbo; Reiter, Russel J.; Tan, Dun-Xian; Garcia, Joaquin J.; Manchester, Lucien C.; Karbownik, Malgorzata; Calvo, Juan R.
Environmental Health Perspectives, Vol. 108, No. 5, May 2000
Oxidative Stress-Related Mechanisms Are Associated with Xenobiotics Exerting Excess Toxicity to Fanconi Anemia Cells
Pagano, Giovanni; Manini, Paola; Bagchi, Debasis.
Environmental Health Perspectives, Vol. 111, No. 14, November 2003
Vitamin E-How Much Is Enough?
Emanoil, Pamela.
Human Ecology, Vol. 28, No. 2, Spring 2000
Food and You: A Guide to Healthy Habits for Teens
Marjolijn Bijlefeld; Sharon K. Zoumbaris.
Greenwood Press, 2001
Librarian’s tip: "Antioxidants and the Role They Play" begins on p. 26
Bad Medicine: Misconceptions and Misuses Revealed, from Distance Healing to Vitamin O
Christopher Wanjek.
Wiley, 2003
Librarian’s tip: Chap. 21 "Learning Your Alpha-Beta-Carotenes: Antioxidants, Pro and Con"
Coffee, Tea, Chocolate, and the Brain
Astrid Nehlig.
CRC Press, 2004
Librarian’s tip: "Antioxidant Effects of Coffee" begins on p. 191
How Science Works: Evaluating Evidence in Biology and Medicine
Stephen H. Jenkins.
Oxford University Press, 2004
Librarian’s tip: Chap. 2 "Do Vitamin C and Other Antioxidants Benefit Health? Using Observational and Experimental Studies to Test Medical Hypotheses"
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