The omega-3 fatty acid is called EPA (eicosapentaenoic acid). It's found in fish such as salmon and mackerel, along with another fatty acid called DHA (docosahexaenoic acid).
Study participants were followed for more than four years, on average. During that time, they all took cholesterol-lowering statin drugs.
The researchers assigned half the participants to also take pills containing highly purified EPA. For comparison, the other participants only took their statins, with no EPA pills.
Then the researchers tracked major coronary events, such as sudden cardiac death, fatal or nonfatal heart attack, or other nonfatal heart problems, in both groups for 4.6 years, on average.
During the study, the vast majority of patients had no major heart problems.
However, 2.8% of those taking EPA along with statins experienced a major coronary event, compared with 3.5% of those only taking statins.
That's a 19% difference, note the researchers, who included Mitsuhiro Yokoyama, MD, of Kobe University in Kobe, Japan.
EPA pills weren't linked to any difference in fatal heart attacks or sudden cardiac death.
When Yokoyama's team took a closer look at the data, they found the EPA advantage only applied to patients with a known history of coronary artery disease.
Patients with high cholesterol but no history of coronary artery disease may also get some heart protection from EPA, but that's not certain, since so few of them had major heart problems during the study.
The researchers conclude that EPA is a "promising treatment" for the prevention of heart problems in Japanese patients with high cholesterol.
Fish is a staple of the traditional Japanese diet. That may partly explain why EPA pills didn't seem to curb fatal heart events. "Our patients could possibly all have had intakes of fish that were above the threshold for prevention of fatal coronary events or sudden cardiac death," write Yokoyama and colleagues.
The researchers didn't ask patients about their diets.
Yokoyama's team also warns that the findings might not apply to people who don't eat lots of fish. "EPA might affect risk only at very high levels of fish intake, such as those common in Japan," they write.
Lastly, the researchers note that they only tested EPA pills, not fish or fish oil. The pills were made in Japan by Mochida Pharmaceutical Co., which funded the study.
Curbing Heart Problems
The study appears in The Lancet, along with an editorial by Dariush Mozaffarian, MD, MPH, DrPH, of the Harvard School of Public Health.
Mozaffarian points out that the study didn't include a group taking an inactive pill (placebo) along with their statins.
Still, the drop in nonfatal heart events in those taking EPA and statins "should not necessarily be discounted," writes Mozaffarian.
He commends the Japanese researchers for their work and calls for further studies.
Mozaffarian takes a back-to-basics approach to preventing heart problems. For instance, he notes in his editorial that modest dietary changes are less risky, less costly, and more accessible than drugs, invasive procedures, or devices.
"We must curb our infatuation with downstream risk factors and treatments, and focus on the fundamental risk factors for cardiovascular disease: dietary habits, smoking, and physical activity," writes Mozaffarian.