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.

Researchers from Harvard School of Public Health (HSPH) and the University of Washington 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.

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.

Mackerel, herring, salmon and sardines are all considered oily fish.