A diet heavy in fish and seafood may lower overall mortality risk by as much as 27 percent, according to researchers at Harvard University and University of Washington.

The researchers found that older adults who have higher blood levels of the omega-3 fatty acids found almost exclusively in fish and seafood lived an average of 2.2 years longer than older adults with lower omega-3 levels.

A diet high in omega-3 fatty acids also cut mortality risk from heart disease by about 35 percent, the researchers reported.

"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 Harvard School of Public Health. "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 consumption of unsaturated fats in fish has long been linked to lowered risk of dying of heart disease.

But Harvard reports the study was the first of its kind to look at how objectively measured blood biomarkers of fish consumption relate to total mortality and specific causes of mortality in a general population.

The researchers examined 16 years of data from about 2,700 U.S. adults aged 65 or older in four communities across America. All of the adults were considered "generally healthy at baseline."

Three fatty acids were associated with significantly lower risk of mortality. Docosahexaenoic acid, or DHA- was most strongly related to lower risk of coronary heart disease (40 percent lower risk). Among the other two fatty acids, eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA)-DPA was most strongly associated with lower risk of stroke death, and EPA most strongly linked with lower risk of nonfatal heart attack. None of these fatty acids were strongly related to other, noncardiovascular causes of death, Harvard reported.

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

The paper "Plasma Phospholipid Long-Chain Omega-3 Fatty Acids and Total and Cause-Specific Mortality in Older Adults," appears online April 1, 2013 in Annals of Internal Medicine.