Omega-3s May Not Prevent Cancer

SANTA MONICA, Calif.--Omega-3 fatty acid intake is not associated with reduced risk of cancer, according to a systematic review supported by the Agency for Healthcare Research and Quality (AHRQ) and the National Institutes of Health's (NIH) Office of Dietary Supplements (ODS), and published in the Journal of the American Medical Association (JAMA) (295, 4:403-15, 2006).

Researchers from the Southern California Evidence-Based Practice Center, the Greater Los Angeles VA Healthcare System, the University of California Los Angeles School of Public Health and Wright State University School of Medicine searched MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials and other databases for relevant articles published from 1966 through October 2005. Unpublished research gathered from "experts in the nutraceutical industry" was also considered. The researchers selected 38 articles based on descriptions of effects of omega-3 essential fatty acid (EFA) consumption on tumor incidence, prospective cohort study design, human study population and effect of omega-3 fatty acids on test groups with different levels of exposure. Two reviewers independently abstracted data concerning cancer incidence, test group characteristics, details on the exposure to omega-3 EFAs, elapsed time between intervention and outcome measurements, and information concerning methodological quality of the studies reviewed.

Analyzing 20 cohorts from seven countries involving 11 different types of cancer and using up to six different ways to categorize omega-3 EFA consumption, 65 estimates of the association between omega-3 fatty acid consumption and cancer risk were reported. Among these, only eight were statistically significant. The researchers elected to forgo pooling of data, as there was a high degree of heterogeneity across the studies. For breast cancer, one significant estimate was for increased risk; seven other estimates did not find a significant association. For colorectal cancer, there was one estimate of decreased risk and 17 estimates without association. For lung cancer, there was one significant association for increased risk, one for decreased risk and four other estimates were not significant. For prostate cancer, one estimate was for decreased risk, one estimate was for increased risk of advanced prostate cancer and 15 other estimates found no significant association. One study for skin cancer found an increased risk. No significant associations for found for aerodigestive cancer, bladder cancer, lymphoma, ovarian cancer, cancer of the pancreas or stomach cancer.

The researchers concluded a large body of literature spanning numerous cohorts from many countries with different demographic characteristics does not provide evidence to suggest a significant association between omega-3 fatty acids and cancer incidence, and noted dietary supplementation with omega-3 fatty acids is unlikely to prevent cancer.

"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 Carolyn Clancy, M.D., director of AHRQ. "This information will help them make informed, evidence-based decisions about their health and heath care."

Clancy added the new study is part of a larger project supported by AHRQ and the Office of ODS, which reviewed scientific evidence supporting the health benefits of omega-3 fatty acids and found consumption of 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 ODS. "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."

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