A free radical is an atom in the body that is damaged and missing one or more electrons, making it unstable. Free radicals are produced in body cells as a normal part of metabolism, for example, as a by-product of fat oxidation. They are also created in the body by exposure to sunlight, x-rays, and pollutants such as tobacco smoke, car exhaust and ozone.

Free radicals attack body cells in a number of ways. They can damage mitochondria (the cells’ own energy powerhouses), rupture cell membranes, and damage, DNA thereby altering or destroying cell function.

The body can normally cope with low levels of free radicals but high levels may initiate or contribute to premature aging, atherosclerosis and heart disease, cancer, cataracts, arthritis, infertility in men, and other degenerative diseases.

Antioxidants are substances that combat or neutralize free radicals before excessive damage occurs to our body cells. Research into antioxidants is in early stages, and much of what is known is speculative. Nevertheless, antioxidants show promise as agents that can prevent or delay many disease processes.

Antioxidants may also help to stop damage occurring to the blood vessel walls by preventing the oxidization of cholesterol within the body. Oxidization of "bad" LDL cholesterol in the bloodstream is thought to play a key role in the development of fatty streaks and atherosclerosis in artery walls – and the accompanying increased risk of angina, heart attack and stroke.

You can make sure you are getting antioxidants by eating a wide variety of foods, particularly plant foods. Dietary antioxidants that you will get from food include vitamins, minerals and phytochemicals (including carotenoids). Vitamins E, C and beta-carotene are the most studied antioxidants for which important roles have been proposed.

Selenium, zinc, manganese and copper also have important roles as do various enzymes such as SOD, Co-Q10 and glutathione peroxidase.