Richard G. Petty, MD

Antioxidants May Raise Cancer Risk?

Regular readers will know that I have for some years now been raising a red flag the wholesale promotion of antioxidants.

The trouble is this: antioxidants are supposed to help rid us of some of the free radicals that have been implicated in a small number of diseases, and may also play a role in some of the physical aspects of aging. However, free radicals are also some of the major cancer killers in the body, so eradicating them – even if it were possible – hardly seems like a good idea.

According to an analysis of a dozen studies including more than 100,000 patients in the Mayo Clinic Proceedings taking antioxidant supplements do not reduce cancer risk.

In fact smokers who take beta carotene supplements could be increasing their risk of smoking-related cancer and death.

Different antioxidants have different effects, and their effects may also vary depending on the part of the body involved.

The researchers looked at 12 trials that compared antioxidant supplements with placebo on cancer incidence and mortality. Antioxidant supplements did not reduce the risk of cancer. When they looked separately at beta carotene, they found the nutrient actually increased cancer risk by 10 percent among smokers. There was also a trend toward a greater risk of dying from cancer with beta carotene supplementation.

Selenium supplements reduced cancer risk by 23 percent among men, the researchers found, but had no effect on women. While vitamin E had no anti-cancer effect overall, supplementation with the nutrient was tied to a 13 percent lower prostate cancer risk.

A large study looking at vitamin E supplementation for prostate cancer is currently underway. While future studies of beta carotene and vitamin E for cancer prevention are very unlikely to show effectiveness, it would be worth doing further studies on selenium.

The moral of the story: we should be going for a balanced diet and a balanced life in general rather than putting our hopes in an over-simplified nutritional message.

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