The idea that fish oil is good for the heart has been around for decades, and most people now treat it as common knowledge. Coverage usually stops there too: "it's good for your heart, eat fish twice a week" and nothing more. Over the past few years, though, two separate research threads pushed the question past heart health and straight into the pace of aging itself.
The first is a randomized trial using epigenetic age clocks: does omega-3 supplementation change the DNA methylation pattern that these clocks read as "biological age"? The second is a cohort analysis built on decades of stored blood samples: does the omega-3 level measured in someone's blood track with how long they actually live? These are different questions with different limitations, and we treat them separately below.
In a substudy of the Swiss DO-HEALTH trial, which enrolled 2,157 people in total, a team led by Heike Bischoff-Ferrari followed 777 participants for three years across eight arms: vitamin D (2,000 IU/day), omega-3 (1 gram EPA+DHA/day) and a home exercise program, alone or in combination. The results were published in 2025 in Nature Aging.
The researchers measured four DNA methylation age clocks: PhenoAge, GrimAge, GrimAge2 and DunedinPACE. These are lab tests that try to estimate how "old" a person's cells look, independent of chronological age.
A three-to-four-month difference is small for a three-year trial, but it isn't nothing โ and importantly, it comes from a randomized controlled trial, which gets closer to causation than an observational study can. Even so, the researchers themselves describe the effect as small, and note that three years is a short window for a question about lifelong aging.
The second strand of evidence comes from a much older and much larger cohort. An analysis by Dariush Mozaffarian and colleagues, published in 2013 in Annals of Internal Medicine, followed 2,692 U.S. adults with an average age of 74 who had no history of coronary heart disease, stroke or heart failure at baseline. Plasma phospholipid omega-3 levels were measured in 1992, and participants were tracked through 2008.
This is an observational study, not a randomized one. People with higher blood omega-3 levels likely eat fish more regularly, may follow a different overall diet, and could have better access to healthcare. The researchers tried to statistically adjust for such confounders, but an observational design can never fully rule them out. A similar pattern showed up separately in a 2021 analysis of the Framingham Offspring cohort (2,240 people, 11-year follow-up): the omega-3 index was among the strongest predictors of all-cause mortality out of 28 fatty-acid metrics measured. We're not repeating the "equivalent to smoking" framing that circulated in press coverage of that second study, because that comparison comes from news articles, not from the paper itself.
The two studies measure different things, and neither hands you a complete prescription on its own. DO-HEALTH shows that a daily 1-gram EPA+DHA supplement has a measurable but small effect over three years โ the most reliable kind of evidence, since it's randomized. The Cardiovascular Health Study and Framingham show that higher blood levels (mostly reflecting regular fish intake) track with longer life, without proving the mechanism is causal.
The most commonly cited dietary benchmark is two servings a week of oily fish (salmon, sardines, mackerel, anchovies). For anyone considering a supplement, DO-HEALTH used 1 gram of EPA+DHA daily, which is roughly in line with many over-the-counter fish oil capsules โ though products vary widely, so check the label. Anyone on blood thinners, facing upcoming surgery, or considering a high dose (above 2-3 grams a day) should talk to a doctor first; high-dose omega-3 can raise bleeding risk and, in some people, LDL cholesterol.
In the DO-HEALTH trial, published in Nature Aging in 2025, 777 people who took 1 gram of omega-3 daily showed three epigenetic age clocks (PhenoAge, GrimAge2, DunedinPACE) slow by an average of 3-4 months over three years. That is a small but consistent effect; vitamin D alone showed no significant effect. Because the trial ran for three years, what happens over a longer period is unknown.
In a 2013 Annals of Internal Medicine analysis of 2,692 people from the Cardiovascular Health Study, the fifth of participants with the highest blood omega-3 levels had a 27% lower risk of death from any cause than the lowest fifth, and lived an average of 2.2 years longer. This is an observational study, so it cannot fully rule out that higher omega-3 levels simply travel alongside other healthy habits.
The two studies measured different things: the DO-HEALTH effect came from a daily 1-gram EPA+DHA supplement, while the Cardiovascular Health Study association came from measured blood phospholipid levels, which largely reflect fish intake. Two servings a week of oily fish (salmon, sardines, mackerel) is a well-established way to raise blood levels. Anyone on blood thinners or considering a high-dose supplement should talk to a doctor first.
"Omega-3's effect on epigenetic age is small but comes from a randomized trial; its link to life expectancy is large but observational. The two shouldn't be confused with each other."
โ The Vivelong Longevity Science Team