NEW YORK (Reuters Health) - Taking antioxidant supplements won't reduce cancer risk, according to a new analysis of a dozen studies including more than 100,000 patients. In fact, the researchers found, smokers who take beta carotene supplements could be increasing their risk of smoking-related cancer and death.

While antioxidants have been touted for cancer prevention, different antioxidants have different effects, and their effects may also vary depending on the part of the body involved, Dr. Aditya Bardia of the Mayo Clinic in Rochester, Minnesota and colleagues note in their report.

To investigate, the researchers looked at 12 trials that compared antioxidant supplements with placebo on cancer incidence and mortality.

Overall, the researchers found, antioxidant supplements didn't 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, Bardia and colleagues did find that 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, the researchers note. While future studies of beta carotene and vitamin E for cancer prevention are "very unlikely" to show effectiveness, they add, such studies of selenium "could be warranted."

SOURCE: Mayo Clinic Proceedings, January 2008.