Omega-3 Fatty Acids and Cancer

Eating fish and other foods high in omega-3 fatty acids doesn't have the wondrous effect on preventing malignancies that it seems to have in warding off heart disease.

As a cancer preventive strategy, omega-3 was left high and dry, reported Catherine H. MacLean, M.D., Ph.D., and colleagues at Rand Health in the Jan. 25 issue of the Journal of the American Medical Association.

The authors noted that their results seem to conflict with laboratory and animal studies suggesting that omega-3 fatty acids may have a protective effect against cancer, but they chalked up this discrepancy to the inadequacies of cancer models, and to differences between omega-3 forms found in foods and in dietary supplements.

In a review of 38 articles describing the effects of omega-3 consumption (either from foods or from dietary supplements) on cancer, Dr. MacLean and colleagues found that "omega-3 fatty acids appear not to affect a mechanism of cancer development that is common across the different types of cancers evaluated in this report. Likewise, there is little to suggest that omega-3 fatty acids reduce the risk of any single type of cancer."

The authors found that among 65 estimates of the association between omega-3 fatty acid consumption and cancer, only eight were statistically significant, and there was conflicting evidence for an association with cancer risk across many of the studies.

For example, they found one study indicating that for breast cancer there was an increased risk for cancer associated with omega-3 (incidence risk ratio 1.47; 95% confidence interval, 1.10-1.98), but three other suggesting a decreased risk (RR, 0.68-0.72). Still seven other estimates showed no significant association between breast cancer risk and omega-3 consumption.

"A large body of literature spanning numerous cohorts from many countries and with different demographic characteristics does not provide evidence to suggest a significant association between omega-3 fatty acids and cancer incidence," Dr. MacLean and colleagues wrote. "Dietary supplementation with omega-3 fatty acids is unlikely to prevent cancer," they concluded.

Source reference: MacLean CH et al. Effects of Omega-3 Fatty Acids on Cancer Risk. A Systematic Review. JAMA. 2006;295:403-415