Older adults who have high blood levels of omega-3 fatty acids — found almost exclusively in fatty seafood — may be able to lower their overall mortality risk by as much as 27 percent and their mortality risk from heart disease by about 35 percent, according to a new study from Harvard School of Public Health (HSPH) and the University of Washington. Researchers found that older adults who had the highest blood levels of the fatty acids lived, on average, 2.2 years longer than those with lower levels.

“Although eating fish has long been considered part of a healthy diet, few studies have assessed blood omega-3 levels and total deaths in older adults,” said lead author Dariush Mozaffarian, associate professor in the Department of Epidemiology at HSPH. “Our findings support the importance of adequate blood omega-3 levels for cardiovascular health, and suggest that later in life these benefits could actually extend the years of remaining life.”

The study — the first to look at how objectively measured blood biomarkers of fish consumption related to total mortality and specific causes of mortality in a general population — appeared online today in Annals of Internal Medicine.

Previous studies have found that fish, which is rich in protein and heart-healthy fatty acids, reduces the risk of dying from heart disease. But the effect on other causes of death or on total mortality had been unclear. With this study, the researchers sought to paint a clearer picture by examining biomarkers in the blood of adults not taking fish oil supplements, to provide the best assessments of the potential effects of dietary consumption of fish on multiple causes of death.

The researchers examined 16 years of data from about 2,700 Americans aged 65 or older who participated in the Cardiovascular Health Study (CHS), a long-term study supported by the National Heart, Lung, and Blood Institute. Participants came from four communities in North Carolina, California, Maryland, and Pennsylvania, and all were generally healthy at baseline. At baseline and regularly during follow-up, participants had blood drawn, underwent physical examinations and diagnostic testing, and were questioned about their health, medical history, and lifestyle.

The researchers analyzed the total proportion of blood omega-3 fatty acids, including three specific ones, in participants’ blood samples at baseline. After adjusting for demographic, cardiovascular, lifestyle, and dietary factors, they found that the three fatty acids — both individually and combined — were associated with a significantly lower risk of mortality. One type in particular, docosahexaenoic acid, or DHA, was most strongly related to lower risk of death from coronary heart disease (CHD) (40 percent lower risk), especially CHD death due to arrhythmia (an electrical disturbance of the heart rhythm) (45 percent lower risk). Of the other blood fatty acids measured, eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA), DPA was most strongly associated with a lower risk of stroke death, and EPA most strongly linked to a lower risk of nonfatal heart attack. None of these fatty acids were strongly related to other, non-cardiovascular causes of death.

Overall, the study participants with the highest levels of all three types of fatty acids had a 27 percent lower risk of total mortality due to all causes.

When the researchers looked at how dietary intake of omega-3 fatty acids related to blood levels, the steepest rise in blood levels occurred when intake increased from very low to about 400 mg per day; blood levels rose much more gradually thereafter. “The findings suggest that the biggest bang for your buck is for going from no intake to modest intake, or about two servings of fatty fish per week,” said Mozaffarian.

Support for the study came from the National Heart, Lung, and Blood Institute and the Office of Dietary Supplements of the National Institutes of Health.