The most up-to-date review of data from 13 prior studies found daily omega-3 fish oil supplement use tied to a significant lowering of risk for heart attack, according to a team led by Dr. JoAnn Manson. She is a professor of epidemiology at Harvard's T.H. Chan School of Public Health, in Boston.
Daily use of the supplement -- typically about 840 milligrams per day -- was also linked to a lower overall risk of dying from heart disease, the review found.
In total, the 13 studies involved data on more than 120,000 adults, a sample size that is 64% larger than any other yet conducted, the researchers said.
Although the findings are encouraging, fish oil remains just one factor in heart health, Manson said in a school news release.
"Public health recommendations should focus on increasing fish consumption, having an overall heart-healthy diet, being physically active, and having other healthy lifestyle practices," she said. However, "this study suggests that omega-3 supplementation may have a role in appropriate patients."
Overall, Manson's team concluded that people who took a fish oil supplement on a daily basis had an 8% drop in their risk for heart attack or death due to coronary heart disease.
The study couldn't prove that fish oil supplements directly caused the improvements in heart health. After all, people who take the supplements might also be doing other things to boost their cardiovascular systems.
However, the researchers pointed out that there was a "dose-response" relationship in the findings: The more omega-3 fish oil a person took in each day, the greater their protection against heart disease.
As a practical matter, that could mean that "high-dose" supplementation -- a daily regimen that exceeds the 840 mg threshold that's the subject of most research -- could be of even greater benefit than lower doses.
There was one exception to these trends, however: No evidence was found to indicate that omega-3 fish oil also helped to decrease stroke risk, the researchers reported.
Two experts in heart health agreed that the supplement may help the heart, but shouldn't be viewed as a cure-all.
"Supplementation only mitigates the risk" for heart trouble, said Katrina Hartog, clinical nutritionist at Lenox Hill Hospital in New York City. "As always, addressing the main risk factors [for heart disease] may be of the greatest benefit to reduce risk of developing chronic disease."
But she said the new data should reassure Americans that fish oil does help.
Dr. Guy Mintz directs cardiovascular health at Northwell Health's Sandra Atlas Bass Heart Hospital in Manhasset, N.Y. Reviewing the new study, he said "there is nothing 'fishy' here: This study is enlightening and reinforces the need for supplemental treatment options for patients at increased risk for cardiovascular events."
Just how might fish oil be working its magic? According to Mintz, "the mechanism of benefit is unknown but may be due to an anti-inflammatory effect and or anti-arrhythmic effect."
He believes that the supplements may be most helpful for patients at known risk for heart disease.
Based on the new data review, "every physician should have a discussion with their patients at increased cardiovascular risk -- including diabetic patients, patients with heart disease, or patients with stents and a history of coronary bypass -- to see how the addition of omega-3 supplementation at an optimal dosage could further reduce their risk for future cardiac events," Mintz said.
The new study was funded by the National Institutes of Health and was published online Sept. 30 in the Journal of the American Heart Association.