A New Endorsement for Fish
Scientists have turned up ample evidence that consumption of seafood high in omega-3 fatty acids may help protect against cardiovascular disease. But the data have usually been indirect, gleaned from food questionnaires used to estimate consumption.
But now a new analysis relying on blood tests and years of clinical exams confirms that higher blood levels of omega-3 fatty acids may reduce the risk for heart disease and death in people over age 65.
The blood tests were used to track the levels of three different types of omega-3 in 2,692 randomly selected people, average age 74 at the start of the study, for 14 years. All were generally healthy and without previous heart disease. None used fish oil supplements.
The study was published online Monday in Annals of Internal Medicine.
There were 1,625 deaths over the 14-year study period. The highest blood levels of the three kinds of omega-3, individually and combined, were associated with the lowest total mortality, and there was a dose-response relationship — that is, as blood levels of omega-3 went up, the risk for death declined.
After adjustment for a number of variables, those in the highest 20 percent in omega-3 blood levels were 27 percent less likely to die of any cause than those in the lowest fifth. Those with blood levels in the highest fifth were also 40 percent less likely to die of coronary heart disease, and 48 percent less likely to die of an arrhythmia than those in the lowest fifth.
There were fewer deaths from stroke in those with the highest levels of omega-3s, but the difference was not statistically significant. Over all, the researchers calculated that those with the highest omega-3 blood levels lived an average of 2.22 more years than those with lowest.
The lead author, Dr. Dariush Mozaffarian, an associate professor of medicine at Harvard, said that the most beneficial levels could be achieved by consuming an average of 400 milligrams of omega-3s a day — the equivalent of weekly consumption of about 3.5 ounces of farmed salmon, 5 ounces of anchovies or herring, or 15 to 18 ounces of cod or catfish.
While greater amounts may have some additional benefits, he said, “The most bang for the buck is going from zero to some.”
Controlled trials have shown that omega-3 fatty acids have various beneficial physiological effects, among them reduced heart rate, lower blood pressure and lower triglyceride production. These effects are modest, the researchers say, but combined they could reduce mortality.
Dr. Kenneth J. Mukamal, an assistant professor of medicine at Harvard, who was not involved in the study, said the work confirmed “older clinical trials showing just this — that omega-3 oil prevented sudden cardiac death.”
The finding that omega-3 levels were associated with lowered risk for death by specific causes, Dr. Mozaffarian said, is novel and important.
“The specificity for heart disease and arrhythmias is very compelling for this being a cause-and-effect relationship,” he said, rather than an association based on general good health or other lifestyle factors.
Still, the authors acknowledge that there may be other variables they were unable to account for.
Would omega-3 supplements work just as well as eating fish? “Some previous trials of supplements showed benefits,” Dr. Mozaffarian said. “Some more recent have not. So I think it’s a little uncertain what’s going on.”
In any case, he said, supplements may be the answer for some people: “If you don’t eat fish, take supplements, and if you want to take supplements in addition to eating fish, no harm in doing that.”
A version of this article appeared in print on 04/02/2013, on page D4 of the NewYork edition with the headline: A New Endorsement for Fish.