Omega-3 fatty acids do not lower cancer risk

NEW YORK (Reuters Health) - Taking dietary supplements containing fish oil (omega-3 fatty acids) or regularly consuming fish does not appear to reduce a person's risk of developing cancer, according to a report in this week's issue of the Journal of the American Medical Association.

However, lead investigator Dr. Catherine H. MacLean said consumers should consider the other health benefits of omega-3 fatty acids before deciding whether to take dietary supplements containing omega-3 fatty acids or to eat more fish.

"There is solid evidence that omega-3 fatty acids reduce heart attacks and overall risk of death among people with heart disease," she explained.

Additionally, although omega-3 fatty acids do not alter levels of total cholesterol, "good" HDL cholesterol, or "bad" LDL cholesterol, evidence suggests that they can reduce levels of triglycerides -- a fat in the blood that may contribute to heart disease, she said.

Despite mixed results on the value of fish oil as a cancer preventive, a number of omega-3-packed dietary supplements claim to protect against the development of cancer.

To determine the validity of these claims, MacLean, of RAND Health, in Santa Monica, California and colleagues reviewed 38 studies published on the topic and calculated "estimates of association" between omega-3 fatty acid intake and 11 different types of cancer.

They failed to find any strong evidence to suggest that omega-3 fatty acids reduce the risk of any type of cancer.

A few studies showed significant associations between dietary omega-3 fatty acid and risk for cancer of the breast, lung, and prostate. But for each of these cancers, there were studies that showed significant associations for increased risk and decreased risk, and far more studies found no association.

No significant associations between fish oil and cancer incidence were evident for lymphoma or for cancer of the mouth, throat, esophagus, bladder, ovaries, pancreas, or stomach.

One study that assessed skin cancer showed an increased risk with omega-3 fatty acid consumption.

"I think the overall message is that omega-3 fatty acids are not a panacea and they do not reduce cancer risk, but they do have some important cardiovascular health benefits," MacLean concluded.

SOURCE: Journal of the American Medical Association, January 25, 2006.