Diet High in Omega-3 Fatty Acids Unlikely to Reduce Risk of Cancer

Diet and Cancer

Taking dietary supplements containing omega-3 fatty acids or regularly consuming fish does not appear to reduce a person's risk of developing cancer, according to the findings of an in-depth analysis of large-scale U.S. and foreign population studies. The results of the analysis, which was supported by HHS' Agency for Healthcare Research and Quality (AHRQ) and the National Institutes of Health's Office of Dietary Supplements, are published in the January 25, 2006, issue of the Journal of the American Medical Association.

Although some lines of research had suggested that people who consume diets high in omega-3 fatty acids are less likely to develop some types of cancer, researchers from the AHRQ-supported Southern California Evidence-based Practice Center in Santa Monica found very little evidence that omega-3 fatty acids reduce any one of 11 different types of cancer. These researchers analyzed findings from a large body of literature spanning numerous groups from many countries and with different demographic characteristics for the effects of omega-3 fatty acids on 11 different types of cancer breast, colorectal, prostate, ovarian, lung, pancreatic, stomach, skin and bladder cancer, as well as aerodigestive cancer and lymphoma.

In addition, these researchers evaluated the literature on the possible effect of omega-3 fatty acids in cancer treatment but did not find a significant association between omega-3 fatty acids and clinical outcomes after tumor surgery.

"These findings will help health care professionals and the public understand what the science shows for the effects of omega-3 fatty acids on cancer risk," said AHRQ Director Carolyn M. Clancy, M.D. "This information will help them make informed, evidence-based decisions about their health and heath care."

Dr. Clancy added that the new study is part of a larger project supported by AHRQ and the Office of Dietary Supplements which reviewed the scientific evidence of the health benefits of omega-3 fatty acids and found that that taking these supplements or eating fish has been shown to help protect against heart disease.

"ODS continues to value the role of systematic reviews of the scientific literature on foods and dietary supplements," said Paul M. Coates, Ph.D., director of the Office of Dietary Supplements. "We have sponsored a series of reviews regarding the potential role of omega-3 fatty acids in the prevention of a variety of health conditions. In this case, there is insufficient evidence to support the preventive effect of omega-3 fatty acids in cancer. These findings, however, should serve as an important signal of the need for rigorous, well-designed preclinical and clinical studies in the field."

After analyzing data from prospective studies conducted in the United States and six other countries Norway, Sweden, Denmark, the Netherlands, Japan and China that involved more than 700,000 patients and in some cases lasted up to 30 years, the researchers found no evidence that omega-3 fatty acids reduce overall risk of cancer.

Fifty-five of the 65 analyses conducted found no effects at all. Only 10 studies yielded statistically significant results, and these were mixed. Omega-3 fatty acids appeared to increase risk for developing some cancer, particularly for breast, prostate and lung cancer, while in other types it appeared to reduce the risk.

However, the data are not sufficient to rule out with certainty the possibility of an association between consumption of omega-3 fatty acids and cancer incidence, according to RAND Health's Catherine H. MacLean, M.D., Ph.D., who led the systematic review. RAND Health is a part of the Southern California Evidence-based Practice Center.

Dr. MacLean also said that although a number of studies suggest that omega-3 fatty acids may play a role in inhibiting tumor growth in laboratory animals, it is not possible to form strong conclusions because of the quality of the studies.

For details, see "Effects of Omega-3 Fatty Acids on Cancer Risk: A Systematic Review," in the January 25, 2006, issue of the Journal of the American Medical Association.

Other reports in this series evaluated the effects of omega-3 fatty acids on cardiovascular outcomes, child and maternal health, cognitive function, asthma, and organ transplantation. All of the reports are available at www.ahrq.gov/clinic/epcix.htm.

The study was part of a larger project supported by AHRQ and the Office of Dietary Supplements that reviewed the scientific evidence of the health benefits of omega-3 fatty acids.