Omega-3: The Well-Oiled Heart

It's hard to miss the raves about oily fish and the beneficial omega-3 fatty acids they contain. But what to make of claims that fatty acids reduce heart attacks and strokes? Two research reports, both reviewing many studies on the subject, came to differing conclusions about the benefits of omega-3s for cardiovascular conditions.

One report found that fish and fish oil had no effect at all in reducing cardiovascular deaths or events among the general population or those at increased risk of heart disease. The other showed that even though seafood is often contaminated with mercury and PCBs, its benefits overwhelmingly outweigh the risks. What's going on?

The first review was done for the Cochrane Collaboration, an organization that reviews studies in order to compile a library of evidence-based medicine. It pooled data from 89 studies and found "no strong evidence" of reductions in overall mortality or declines in heart attacks or strokes.

One of the authors of the review, Lee Hooper, a lecturer in research synthesis and nutrition at the University of East Anglia in Norwich, England, says that the research doesn't show that fish oil doesn't work, but "it introduces a note of caution before we go all out for it." Any substance powerful enough to help some conditions could worsen others. Omega-3s may reduce the risk of one type of stroke but increase the risk of another.

The review does show that people who have already suffered a heart attack have reduced mortality if they take fish oil supplements. In Europe, in fact, a strong supplement called Omacor is routinely prescribed in such cases, and is newly available in the U.S. But because so many of the component studies looked at people with heart disease, their already-elevated risk of heart attack makes it hard to discern whether fish oil can help prevent cardiovascular disease in the first place.

The sunnier review, published in the Journal of the American Medical Association included three more studies not considered in the Cochrane report. It found that eating one to two weekly servings of oily fish, such as salmon, trout, or mackerel, reduces the risk of heart-related death by 36 percent and the overall death rate by 17 percent.

"There is overwhelming evidence for a benefit
in reducing deaths from heart attacks," says Dariush Mozaffarian, an instructor in medicine at Harvard. "The evidence is stronger than for any other dietary factor we know of." He cites the three additional studies as strong enough to show a significant effect that did not emerge in the Cochrane results, though the difference could also result from stricter standards applied to the inclusion of studies in the Cochrane research.

Mozaffarian was surprised that his study yielded only weak evidence of harm to adults from mercury contaminants found in fatty fish. Some constituent studies actually indicated the metal, a known neurotoxin, had positive effects on the brain. "There was no consistent evidence," he said, which is why the risk-benefit calculation so clearly favored eating fish.

Bottom Line: One to two servings a week of oily fish or daily fish-oil supplements are heart-healthy, but it's not yet known whether higher doses pose risks for some people.