An antioxidant is any molecule that slows down or prevents oxidation reactions. Originally, oxidation reactions were defined as chemical reactions with oxygen. More recently, oxidation reactions have been described as reactions in which an atom or molecule loses an electron.

Oxidation is a natural part of life. Excessively high antioxidant levels are detrimental to health. Some people have suggested that oxidation reactions contribute to heart disease, declines in cognitive abilities, and cancer.

“Vitamin C, vitamin E, and beta-carotene have been shown to be antioxidants in a test tube, and it is often claimed that they and many other substances are able to function as antioxidants in the body. However, whether any molecule can act as an antioxidant depends on its environment, and it is not clear which of these can be counted on to work in your body. Further, even if they act as antioxidants in the body, it is not clear that they will have any effect on heart disease or cancer,” says Gerda Endemann, biochemist and author of Fat is Not the Enemy (Endemann, 2002).

In a five-year study, male smokers with angina (chest pain due to heart disease) were given vitamin E, beta-carotene, both, or a placebo. There was no benefit realized from any of these treatments in terms of severe angina or heart attacks. Beta-carotene and vitamin E were actually associated with increased death from heart disease. Male smokers who had previously suffered a heart attack and were taking beta-carotene in this study were 1.75 times as likely to die as were those taking a placebo (Endemann, 2002).

In another large study of 18,314 smokers, former smokers, and asbestos-exposed workers, the combination of beta-carotene and vitamin A was shown to be harmful rather than protective (Omenn, et al., 1996). The researchers concluded “the combination of beta carotene and vitamin A had no benefit and may have had an adverse effect on the incidence of lung cancer and on the risk of death from lung cancer, cardiovascular disease, and any cause in smokers and workers exposed to asbestos.”

In another study, beta-carotene (50 mg) or a placebo was given to 22,000 physicians on alternate days for an average of 12 years. There was no difference between the groups in the incidence of heart attacks or deaths from cardiovascular disease (Endemann, 2002).

Another study found vitamin E was probably effective in reducing the chances of restenosis–the rapid narrowing and hardening of the arteries that can happen immediately following surgical procedures carried out to open up clogged arteries (Endemann, 2002). Kang and colleagues (Kang, et al., 2006) concluded that the long-term use of vitamin E supplements did not provide cognitive benefits among generally healthy older women.

Grodstein and colleagues (Grodstein, et al., 2003) investigated the relation of high-dose antioxidant supplements on cognition. Information on the use of specific supplements containing vitamins E and C was collected biannually via mailed questionnaires beginning in 1980 from 14,968 community-dwelling women who participated in the Nurses’ Health Study. After looking at the data, the researchers concluded that the use of specific vitamin E supplements, but not specific vitamin C supplements, might be related to modest cognitive benefits in older women.

Antioxidants in moderation are good for your health. If you’re following a balanced diet that includes fruits, vegetables, whole grains, nuts, and seeds, your antioxidant levels are probably fine. If your diet is lacking in antioxidants an antioxidant supplement will do.

Don’t go overboard with supplements; unnaturally high doses can be harmful to your health. Oxidation is a natural chemical process that occurs in the body and is required for life.