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Fish Oil Won't Fight Cancer

But finding doesn't mean omega-3 fatty acids aren't heart-healthy, experts add

TUESDAY, Jan. 24, 2006 (HealthDay News) -- They may be great for the heart, but the omega-3 fatty acids found in fish and fish oil supplements do nothing to prevent cancer, a major analysis finds.

A new review of more than 38 studies on the subject finds no evidence that diets rich in fish fight any kind of malignancy.

Omega-3 fatty acids "definitely have health benefits, but they are not a panacea. Preventing cancer is not one of the things omega-3 fatty acids do," said lead researcher Dr. Catherine MacLean, a natural scientist at Rand Health and a rheumatologist at the Greater Los Angeles VA Healthcare System.

The study, supported by the U.S. Agency for Healthcare Research and Quality (AHRQ) and the National Institutes of Health, appears in the Jan. 25 issue of the Journal of the American Medical Association.

An earlier meta-analysis, also funded by AHRQ, found that diets rich in omega-3 fatty acids did have a beneficial effect on cardiovascular health.

But evidence of any protection against cancer has been more elusive.

"There was a plausible mechanism," MacLean said. "Omega-3s are integral to some of the inflammatory pathways that are also common to cancer, so the idea was that if you had more omega-3s maybe that would dampen this inflammatory process."

But proof for the theory was scanty.

"I think there were a lot of high hopes, but very little evidence," said AHRQ director Dr. Carolyn Clancy. While some research -- mostly animal studies -- suggested omega-3s might have an anti-cancer effect, other studies found no such link.

"So the office at the NIH that deals with dietary supplements asked AHRQ to do a very rigorous review of the studies that had been done," Clancy explained.

In the study, MacLean's group analyzed data from studies conducted over the past 40 years.

The vast majority showed no effect of even high-dose omega-3 fatty acids on the incidence of a wide range of cancers, including breast, colon, lung and prostate malignancies, the researchers found.

Colleen Doyle, director of nutrition and physical activity at the American Cancer Society (ACS), said the finding was "not surprising," since the evidence had always been slim that the nutrient might fight cancer.

But she added that the results would not change current ACS dietary guidelines. "We will still recommend that people include fish in their diets. It's a source of healthy fat, it's associated with a reduced risk for heart disease, and we'd rather see people eat fish with healthier fats than eat red meat with unhealthy fats," she said.

Doyle said healthy diets can discourage cancer by keeping obesity at bay. "Being overweight, especially, increases circulating hormones such as estrogen and insulin that we know are associated with cancer cells and tumor growth," she explained.

MacLean agreed, adding that fish-rich diets are proven to fight heart disease.

"The results of this study need to be taken in the context of the body of literature on omega-3 fatty acids," she said. "We know that for people with cardiovascular disease, omega-3s reduce the risk of having another heart attack and they reduce the risk of arrhythmias in people who have had heart attacks. They also reduce mortality in people with cardiovascular disease."

"Eating fish, as opposed to a hamburger with cheese and bacon, would be a great idea, in general," Clancy added. "And it is not going to hurt you."

More information

For more on how diet and exercise can fight cancer, head to the American Cancer Society.

SOURCES: Catherine MacLean, M.D., Ph.D., assistant professor, medicine, natural scientist, Rand Health, and rheumatologist, Greater Los Angeles VA Healthcare System, Santa Monica, Calif.; Carolyn Clancy, M.D., director, U.S. Agency for Healthcare Research and Quality, Rockville, Md.; Colleen Doyle, M.S., R.D., director, nutrition and physical activity, American Cancer Society; Jan. 25, 2006, Journal of the American Medical Association
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