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Free Radicals

What are Free Radicals?


Updated March 01, 2012

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Free radicals are unstable molecules produced when your body breaks down food, or when your body is exposed to radiation or contaminants (such as tobacco smoke). Overproduction of free radicals can result in oxidative stress, a destructive process known to harm certain cell structures, such as cell membranes and DNA.

Free Radicals and Disease

Free radicals and oxidative stress have been found to play a role in the development of many diseases, including the following:

Antioxidants and Free Radicals

Laboratory research suggests that natural substances known as antioxidants can neutralize free radicals and protect against oxidative stress. Examples of antioxidants include:

While they are available in supplement form, antioxidants are also found in a number of foods and natural remedies, such as:

Should You Take Antioxidant Supplements to Fight Free Radicals?

To date, there is little scientific support for the theory that taking antioxidant supplements can fight free radicals and prevent disease. In fact, some studies suggest that consuming antioxidants in high doses -- especially beta-carotene and vitamin E -- may actually harm health. What's more, the National Center for Complementary and Alternative Medicine cautions that the synthetic antioxidants found in some supplements may not offer the same benefits as antioxidants found naturally in foods.

Some studies, however, show that people who eat more antioxidant-rich foods may have a lower risk of certain chronic diseases, possibly due to the antioxidants' effects on free radicals.


National Cancer Institute. "Antioxidants and Cancer Prevention: Fact Sheet". July 2004.

National Center for Complementary and Alternative Medicine. "Antioxidant Supplements for Health: An Introduction". NCCAM Publication No. D450. May 2010.

National Institutes of Health. "Antioxidants: MedlinePlus". September 2010.

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