Nicholas Bakalar / New York Times News Service

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 older than 65.

The blood tests were used to track the levels of three 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 last week 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.