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Eating fish or seafood twice a week may be the secret to longer life, a new study reveals.

Researchers found that older adults who had the highest blood levels of fatty acids found in fish and seafood 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," lead author Dariush Mozaffarian, associate professor in the Department of Epidemiology at Harvard School of Public Health (HSPH) said in a statement. "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 published April 1 in the Annals of Internal Medicine looked at how blood biomarkers of fish consumption relate to total mortality and specific causes of mortality in a general population.

Past studies revealed that fish, which is rich in protein and heat-healthy fatty acids reduces the risk of dying from heart disease.  However, researchers said that fish consumption's effect on other causes of death or on total mortality has been unclear.

To find out the impact of fish consumption on total mortality, Mozaffarian and his team examined biomarkers in the blood of adults not taking fish oil supplements.

Researchers looked at 16 years of data from about 2,700 U.S. adults aged 65 or older who were part of the Cardiovascular Health Study (CHS), a long-term study supported by the National Heart, Lung, and Blood Institute.  Researchers said participants were from four U.S. communities in North Carolina, California, Maryland, and Pennsylvania, and were all generally healthy at the start of the study. Participants gave blood samples, underwent physical examinations and diagnostic testing and were asked about their health status, medical history and lifestyle.

Researcher they analyzed the total proportions of blood omega-3 fatty acids, including DHA, EPA and DPA in the blood samples at the start of the study.

Even after accounting for demographic, cardiovascular, lifestyle and dietary factors, researchers found that levels of the three fatty acids, both individually and combined, were associated with significantly lower risk of mortality.

However, researchers found that DHA (docosahexaenoic acid) was most strongly related to lower risk of coronary heart disease.  DPA (docosapentaenoic acid) was most strongly associated with lower risk of stroke death, and EPA (eicosapentaenoic acid) was most strongly associated with lower risk of nonfatal heart attack.

Overall, researchers found that participants who ate the most fatty fish and seafood as measured by their blood samples, had a 27 percent lower risk of all cause mortality and 35 percent lower risk of dying from heart disease.

But just how much fish should you eat? Researchers looked at how dietary intake of omega-3 fatty acids related to blood levels and found that the steepest rise in blood levels occurred when going from very low intake to about 400 mg per day.  Researchers said 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," Mozaffarian concluded.