Vitamin pills might not block cancers

The analysis looked at antioxidant pills, not at antioxidant vitamins found in food.

A new analysis of published studies concludes that anti-oxidant supplements might not provide protection against several cancers - and could increase the risk of death.

While some experts say the report adds to the growing case against the use of antioxidant supplements, others question the researchers' methods and conclusions. They say the supplements have benefits not reflected in this report.

The findings, published in the October 2 issue of The Lancet, are based on an analysis of 14 randomised trials involving more than 170,000 patients taking antioxidant supplements or placebos. The trials reported on patients who developed oesophageal, gastric, colorectal, pancreatic or liver cancer.

There is "no convincing evidence that beta-carotene, vitamin A, vitamin C and vitamin E or their combinations may prevent gastrointestinal cancers. These antioxidant supplements may even increase mortality," study co-author Goran Bjelakovic, a professor in gastroenterology and hepatology at the University of Nis in Yugoslavia, said.

The analysis looked at antioxidant pills, not at antioxidant vitamins found in food. Nutrition experts remain in nearly universal agreement that antioxidants found in fresh fruit, vegetables and other whole foods have important benefits. Vitamin-rich whole foods should form the core of a healthy diet, they say.

Some experts said the report sheds new light on an existing concern.

"What it does is confirm what we're already learning about antioxidants and heart disease, and that is that they don't provide the protection that we once thought they would," said David Schardt, a nutritionist at the Center for Science in the Public Interest, a Washington-based advocacy group.

Paul Limburg, director of the Mayo Clinic's gastrointestinal neoplasia clinic, said "antioxidants have demonstrated lots of appeal" in other types of research, such as studies based on self-reports of previous supplement use.

But data derived from clinical trials - studies that follow over extended periods people who take either supplements or an inert placebo - "have been strikingly unremarkable," he said. Still, Limburg says, the study is not definitive.

Other experts caution against drawing broad conclusions. David Forman, a University of Leeds cancer epidemiologist said he "would be very reluctant to draw any conclusions regarding mortality from the evidence that's been presented."

The Council for Responsible Nutrition, a trade association representing dietary supplement suppliers and manufacturers, questioned the researchers' decision to do a meta-analysis of studies that investigated a variety of antioxidants, rather than analysing them as individual nutrients.

"They're violating one of the basic tenets (of meta-analysis) by combining things that shouldn't be combined," said John Hathcock, vice-president of scientific and international affairs at the council.

Some antioxidants are known to have opposing effects, so in a study population taking two supplements, the benefits of one may be masked by the negative effects of the second, he said.

In addition, participants in the studies took high doses of antioxidants, which the authors said might contribute to the negative findings.

Participants in the studied trials took doses considerably higher than those found in multivitamins and some antioxidant supplements.

For instance, every one to two days they took between 1,500 and 15,000 micrograms of vitamin A, compared with the recommended intake of 700 micrograms for most women and 900 micrograms for most men. Study participants took 30 to 600 milligrams of vitamin E, compared with a recommended intake of 15 milligrams daily for most adults.

Not all antioxidant supplements were found to be without benefit or potentially risky. Selenium appears to be an exception, Bjelakovic said, potentially leading to a reduction of gastrointestinal cancers.

Selenium has been found to offer other potential benefits, leading the National Cancer Institute to sponsor further study into its effects. NCI is funding a clinical trial to see if selenium and vitamin E reduce the risk of prostate cancer.

Two trials of beta-carotene included in the analysis drew criticism from some experts. The trials, which found that beta-carotene had harmful effects, included participants who were smokers or had been exposed to asbestos and were therefore at higher risk for cardiovascular disease and lung cancer.

"No one can tell what was responsible for their increased risk," said Jeffrey Blumberg, a nutrition professor at Tufts University. "Basically this (beta-carotene research) is driving the entire conclusion of this report."

But other previous reports conclude that antioxidant supplements are of limited value. A meta-analysis in the July issue of the Archives of Internal Medicine looked at seven trials involving vitamin E supplementation.

It found that the supplements did not help prevent cardiovascular disease and that patients' assumptions about unproven benefits may keep them from developing a healthy lifestyle.

© Los Angeles Times-Washington Post News Service