After years of swimming in suspicions that fish confer health benefits, a new study by researchers at the Harvard School of Public Health and University of Washington found conclusive evidence that omega-3 fatty acids corresponded to a reduced risk of death in the elderly, especially from cardiovascular disease. In older adults, higher blood levels of these fatty acids may even increase lifespan.

The study, published online in the Annals of Internal Medicine, looked at data across 16 years on 2,700 participants aged 65 or older, who were surveyed in the National Heart, Lung, and Blood Institute’s Cardiovascular Health Study.

Those with the highest bloods levels of omega-3s lived an average of 2.2 years longer than their counterparts with lower levels and faced a 27 percent lower risk of mortality.

In order to avoid the error and potential bias of self-reported estimates of fish intake, researchers used blood biomarkers to measure omega-3 levels. Unlike previous studies using such biomarkers, the researchers expanded the focus of study beyond heart health alone.

“Ours is the first study to assess how objectively measured omega-3 levels relate to total deaths, and deaths from multiple causes, in a general population,” wrote Dariush Mozaffarian, lead author of the paper and associate professor of epidemiology at HSPH, in an email.

Mozaffarian and his colleagues identified three fatty acids that appeared most responsible for observed reductions in mortality. Each was linked to a different ailment: coronary heart disease, nonfatal heart attack, or stroke.

“The higher levels of omega-3s in our study would correspond to about 3.5 oz. of farmed salmon, 5 oz. of anchovies or herring, or 15-18 oz. of cod or catfish per week,” wrote Mozaffarian. “The biggest bang-for-your-buck appears to be going from no intake to some.”

Mozaffarian suggested 400 milligrams—or two servings—of fatty or oily fish per week as a healthy option and added that fish oil supplements do not seem to be as effective.

Although dietary fat traditionally has a bad reputation, the HSPH study indicates that fat can actually be beneficial.

“Vegetable oil fats and fats from seafood are healthy,” wrote Mozaffarian. “Guidance should not be simply, ‘If you must eat fat, eat these fats,’ but ‘Increase the intakes of healthy fat, especially as a replacement for refined carbohydrates, starches, and sugars or unhealthy fats.’”

Existing studies have provided clues into the cellular and subcellular functions of omega-3s, but future research is needed to identify the specific genetic and molecular pathways affected by omega-3 fatty acids to better understand how they benefit human health.