Fish, fish, it’s good for the heart. Yeah, you know that. But here’s a fact about fish you probably haven’t heard—eating it may add 2.2 years to your life. And the biggest surprise is how little you actually have to consume to lengthen your life, according to a new Harvard study.

Fish is rich in omega-3 fatty acids that protect against heart disease, inflammation, Alzheimer’s disease, depression and many other serious problems, previous studies have shown. What makes the new research so compelling? Rather than relying just on participants’ own subjective (and potentially inaccurate) reports of how much fish they eat, researchers also used an objective biomarker—blood tests that measured how much omega-3 people actually had circulating in their blood. Then they cross-referenced those measurements against the participants’ reported food intake data.

The study included almost 2,700 men and women age 65 or older. At the start of the study, all participants were generally healthy and none were taking fish oil pills. Their blood was tested for levels of three specific omega-3 fatty acids—eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). Such blood levels reflect a person’s omega-3 consumption over the previous four months or so. (For more info on omega-3 blood testing, read “Omega-3 Blood Test Reveals Deficiency.”) Participants were then followed for 16 years or until they died. Researchers obtained death certificates or other medical records that listed cause of death, then performed a detailed analysis, adjusting for various risk factors (demographics, age, lifestyle, etc.).

What the researchers found: Participants with the highest total omega-3 blood levels lived, on average, 2.2 years longer than those with the lowest levels. In addition to being 35% less likely to die from cardiovascular disease, these participants were 27% less likely to die from any cause during the study period.

Looking at the specific effects of the various types of omega-3s, researchers found that higher levels of DHA were linked to a 45% reduction in death from heart rhythm disorders…DPA was associated with a 47% drop in the risk of dying from stroke…and EPA was linked with a 28% lower risk for nonfatal heart attack.

Fish is a very important dietary source of omega-3s, but it’s not the only one—other good sources include flax seeds, walnuts, soybeans and grass-fed beef.

You don’t have to gorge on fish or other omega-3-rich foods to reap the longevity benefits. In the study, blood levels of omega-3s showed the most pronounced increase when comparing participants who consumed little or no omega-3s with those who had an average omega-3 intake of approximately 400 mg per day (that’s about 2,800 mg per week)—about the amount you would get from eating two servings of fatty fish (such as salmon, sardines or tuna) every week. At higher levels of omega-3 consumption, blood levels continued to rise but they did so much more gradually. This suggests that the biggest “bang for your buck” occurs when a person goes from eating little or no fish to regularly eating modest amounts of fish.

Because this study focused on people who did not take fish oil pills, it is not known whether using supplements would produce similar benefits—but other studies that have looked at the effects of omega-3 supplementation have shown mixed results. So if you rely on fish oil supplements because you’re not fond of the taste of seafood, try the tasty recipes in “How to Make Good-for-You Fish Taste Good, Too“—you’ll never want to go another week without fish.