Antioxidant Supplements Don't Protect Against Prostate Cancer

But vitamin E may be of some help to smokers, study finds

TUESDAY, Feb. 14, 2006 (HealthDay News) -- A study of nearly 30,000 men finds that long-term use of popular antioxidant supplements does not protect most nonsmoking men from developing prostate cancer.

However, men who smoke do appear to gain some protective benefit from vitamin E supplements, the study found.

"Vitamin E supplementation was related to reduced risk for prostate risk in people who were smokers -- but not everyone in general," said lead researcher Richard B. Hayes, senior investigator in the division of cancer epidemiology and genetics at the U.S. National Cancer Institute.

Prostate cancer remains one of the most common cancers in men -- the American Cancer Society estimates about 234,460 new cases will be diagnosed this year. When caught early, the malignancy is highly treatable. Nevertheless, the cancer society estimates that 27,350 American men will die of the disease in the coming year.

But could antioxidants, which fight disease by lowering levels of dangerous free radical molecules in cells, help reduce the risk?

"There has been definite interest in their use, based on a few earlier studies that have been done," Hayes said. "I wouldn't say there's been a consensus on the issue, though."

Reporting in the Feb. 15 issue of the Journal of the National Cancer Institute, Hayes' team calculated the risk of prostate cancer for 29,361 men aged 55 to 74, all of whom were participants in the Prostate, Lung, Colorectal and Ovarian (PLCO) Screening Trial.

Part of the data included the participants' daily intake of popular antioxidant supplements such as beta carotene, vitamin E and vitamin C.

This observational trial followed the men for an average of slightly more than four years. However, Hayes stressed that "many of these people had been taking these supplements for many [more] years" prior to the study.

Over the total eight-year span of the study, 1,338 of the men developed prostate cancer.

According to the researchers, long-term use of antioxidant supplements had no impact on the risk for prostate malignancy for most nonsmokers. A small subgroup of men with very low levels of dietary beta carotene did appear to derive some protective benefit from beta carotene supplements, the researchers noted.

In keeping with the results of previous trials, smokers gained some protection against prostate cancer from long-term use of vitamin E, the researchers reported.

The exact reasons for that benefit remain puzzling. "Smoking itself isn't strongly related to prostate cancer," Hayes said, "but our study and a number of others have shown that vitamin E supplementation tends to be much more effective in smokers."

Andrew Shao is vice president for scientific and regulatory affairs at the Washington-based Council for Responsible Nutrition, which represents the supplements industry. He noted that "smokers tend to be lower in their antioxidant status -- their blood levels are significantly lower than non-smokers." Vitamin E supplement may help redress that deficiency, he said.

Hayes agreed. "That seems like a reasonable possibility," he said.

Shao said the study was well-designed, but because it is observational -- comparing random, self-reported use of antioxidants against disease incidence -- it is necessarily flawed.

"There are a number of confounders," Shao said, "and people rarely report accurately what they eat or what they use in supplements." So it's possible, he said, that more study might yield positive results for nonsmokers, as well.

As for smokers, no one is advocating that they use vitamin E as an excuse to keep puffing away.

"The best thing people can do is to stop smoking," Shao said. "It's sad, though, because some people do use this kind of justification -- pop a supplement to counteract all the bad effects of smoking. It won't work."

More information

For more on prostate cancer, visit the U.S. National Cancer Institute.

SOURCES: Richard B. Hayes, Ph.D., senior investigator, division of cancer epidemiology and genetics, U.S. National Cancer Institute, Bethesda, Md; Andrew Shao, Ph.D., vice president, scientific and regulatory affairs, Council for Responsible Nutrition, Washington, D.C.; Feb. 15, 2006, Journal of the National Cancer Institute
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