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Are Antioxidant Supplements Harmful?

Sep 4, 2011 | By Robert DiPardo
Are Antioxidant Supplements Harmful?
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Cellular processes such as oxidation produce harmful chemicals called free radicals. These radicals can damage cells and tissues throughout the body and are partly responsible for a variety of diseases. Antioxidants, chemical compounds that can neutralize free radicals and render them harmless, are produced by the body and contained in foods such as fruits and vegetables. Dietary supplements are another source of antioxidants, and these supplements are generally regarded as safe. Clinical studies, however, have shown that antioxidant supplements can produce certain harmful effects.

Nature of Antioxidants

Oxidative stress is the term scientists use to describe damage to cells caused by reactive chemicals called free radicals. These free radicals arise from normal cellular processes and from exposure to environmental hazards such as cigarette smoke and radiation. In order to combat the harmful effects of free radicals, the body produces chemicals called antioxidants. Two of the more important of these are alpha-lipoic acid and glutathione, small organic molecules synthesized in the body's cells. The body also makes use of antioxidants in foods and dietary supplements. These have a wide range of chemical structures.

Antioxidant Supplements and Mortality

In an article in the February 2007 issue of "The Journal of the American Medical Association," researchers presented the results of an analysis of 68 clinical trials concerning the effect of antioxidant supplements on the death rate, or mortality, of the study subjects. The clinical trials included supplements containing beta-carotene, vitamin A, vitamin C, vitamin E and selenium. Taking into account the low-bias trials covering 180,938 subjects, the researchers found that beta-carotene, vitamin A and vitamin E taken either alone or in combination increased mortality to a significant extent. In contrast, vitamin C and selenium did not appear to influence mortality. Low-bias trials are those that are relatively free of systematic errors in the design, conduct or analysis of the study.

Antioxidant Supplements and Skin Cancer

In the September 2007 issue of "The Journal of Nutrition," scientists reported on the results of a clinical trial to determine the effect of an antioxidant supplement on the occurrence of skin cancer. Trial participants — 7,876 women and 5,141 men — were given either a placebo or a once-daily capsule containing an antioxidant mixture consisting of vitamins C and E, beta-carotene, selenium and zinc. Analysis of study results after 7.5 years revealed that for women, the occurrence of skin cancer was higher in those who took antioxidants relative to those on placebo. For men, the researchers found no difference in skin cancer frequency between the antioxidant and placebo groups.

Harmful Effects in Rats

Using a rat model, researchers studied the effects of long-term administration of moderate to large amounts of the food-based antioxidants lycopene, quercetin and resveratrol given individually. They also studied the effects of administration of a mixture of lycopene and quercetin. Based on their observations, reported in the October 2003 issue of "Food and Chemical Toxicology," the scientists concluded that the antioxidant supplements caused precancerous sores in the rats' livers as well as damage to the DNA of certain cells of their immune system.

References

Article reviewed by Holland Hammond Last updated on: Sep 4, 2011

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