Omega-3 fatty acids are one of the few nutritional interventions with randomised-trial evidence for slowing biological ageing as measured by epigenetic clocks. In the 2025 DO-HEALTH analysis, daily omega-3 slowed several markers of ageing modestly, and in combination with vitamin D and strength training the effect was larger still. The case for omega-3 and longevity is real but measured — here is what the evidence supports, and how to act on it.
The DO-HEALTH trial: omega-3 and the epigenetic clock
DO-HEALTH was a three-year randomised trial in more than 2,000 relatively healthy adults aged 70 and over across Europe. It used a factorial design testing eight combinations of three cheap, accessible interventions: vitamin D3 at 2,000 IU/day, marine-derived omega-3 at 1 g/day, and a simple home strength-training programme of about 30 minutes three times a week.
An analysis published in Nature Aging in February 2025, carried out with epigenetic-clock pioneer Steve Horvath, measured biological ageing using next-generation DNA-methylation clocks — including PhenoAge, GrimAge, GrimAge2 and the pace-of-ageing measure DunedinPACE. The finding: omega-3 supplementation slowed biological ageing across several of these clocks by up to around four months over the three years, with standardised effects roughly in the range of three to four months, regardless of sex, age or body-mass index. Combining omega-3 with vitamin D and exercise produced a larger effect on one of the clocks.
Four months over three years is a small effect, and it is fair to call it that. But it came from an inexpensive, low-risk intervention in a real randomised trial, and it is one of the first human trials to show any supplement moving validated epigenetic clocks at all. That is why it matters.
What omega-3 did — and did not — do for health outcomes
Honesty about the broader DO-HEALTH results is important. The trial’s primary clinical endpoints — blood pressure, non-vertebral fractures, physical performance, infection rate and cognition — did not reach statistical significance for any single intervention. In other words, omega-3 did not deliver a dramatic across-the-board win.
Secondary and follow-up analyses were more encouraging. Omega-3 was associated with roughly a 10% reduction in total falls and fewer injurious falls over three years, and with reduced rates of certain infections. These are the kinds of outcomes that compound into healthspan in older adults, but they emerged from secondary analyses and should be read as supportive signals rather than definitive proof. The epigenetic-ageing result sits alongside them as the most novel finding.
EPA, DHA and why the type matters
“Omega-3” is not one molecule. The two that matter for cardiovascular and ageing biology are the long-chain marine fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). ALA, the plant omega-3 found in flax and walnuts, converts to EPA and DHA only inefficiently in humans, so plant sources alone rarely raise marine omega-3 status much.
EPA and DHA are incorporated into cell membranes, where they influence membrane fluidity, generate anti-inflammatory signalling molecules called resolvins and protectins, and support cardiovascular and neural function. The anti-inflammatory action is the most plausible link to slower biological ageing, since chronic low-grade inflammation accelerates several hallmarks of ageing.
The Omega-3 Index: measuring your status
Unlike most supplements, omega-3 has a validated blood biomarker: the Omega-3 Index, which measures the combined EPA and DHA content of red blood cell membranes as a percentage of total fatty acids. It reflects long-term intake rather than what you ate yesterday.
The commonly cited target is an index of 8% or higher, which observational work associates with the greatest cardioprotection; an index below about 4% sits in the least-protected range, and 4–8% is intermediate. In analyses of the Framingham Offspring cohort, a higher omega-3 index was a strong predictor of lower all-cause mortality over follow-up. These are observational associations, not proof that raising your index to a number extends your life — but the Omega-3 Index is one of the more actionable biomarkers available, because it is directly modifiable through diet and dosing. It belongs on the shortlist of tests worth considering in a longevity workup; see our guide to which longevity tests actually matter.
Food first, then supplements
For most people the simplest route to a healthy Omega-3 Index is oily fish. Salmon, mackerel, sardines and anchovies are rich in EPA and DHA, and populations with high fish intake tend to have high omega-3 indices. The contrast is instructive: Japan, with a traditionally fish-heavy diet, has a population-average omega-3 index well above that of Western countries, and correspondingly higher longevity — one of many factors, but a telling one for readers across Asia where excellent seafood is abundant.
Two to three servings of oily fish a week will move the index substantially for many people. Supplements make sense when fish intake is low, when you follow a plant-based diet (algal oil provides EPA and DHA directly, without fish), or when a measured index is low despite reasonable fish consumption.
Sensible dosing
The DO-HEALTH ageing benefit came from just 1 g/day of marine omega-3, a modest dose. Typical longevity-oriented intakes range from roughly 1 to 2 g/day of combined EPA plus DHA, ideally guided by a measured Omega-3 Index and adjusted upward only if the index stays low. A few practical points:
- Check the label for actual EPA + DHA. A “1,000 mg fish oil” capsule may contain only 300 mg of EPA plus DHA; read the real numbers, not the headline weight.
- Quality and freshness matter. Oxidised (rancid) fish oil is counterproductive. Choose reputable brands with low oxidation and third-party testing.
- Mind the responsible-use notes. High doses can have a mild blood-thinning effect, which is relevant if you take anticoagulants or are approaching surgery — worth discussing with a clinician.
Omega-3 pairs naturally with the other two DO-HEALTH levers. Strength training is the one with the deepest independent evidence for healthy ageing — see why grip strength tracks so closely with longevity — and vitamin D’s effect on biological age is the subject of its own randomised signal. The DO-HEALTH message is that combining them beats any one alone.
Frequently asked questions
Does omega-3 really slow ageing?
In the DO-HEALTH trial, daily omega-3 slowed several epigenetic-clock measures of biological ageing by up to about four months over three years. That is a small but genuine randomised effect, and the combination with vitamin D and exercise was larger. It is slowing the pace of ageing modestly, not reversing it.
What is a good Omega-3 Index?
An index of 8% or higher is the commonly cited target associated with the greatest cardioprotection, while below about 4% is the least protected range. The index measures EPA and DHA in red blood cell membranes and reflects long-term intake, so it is a practical way to check whether your diet or supplement dose is working.
Can I get enough omega-3 from food?
Often, yes. Two to three servings a week of oily fish such as salmon, sardines or mackerel will raise most people’s Omega-3 Index substantially. Plant sources (flax, walnuts) provide ALA, which converts poorly to EPA and DHA, so vegetarians usually need an algal-oil supplement to reach a healthy index.
How much fish oil should I take?
The DO-HEALTH benefit used 1 g/day of marine omega-3. Many longevity-oriented regimens use 1–2 g/day of combined EPA plus DHA, guided by a measured Omega-3 Index. Check labels for the actual EPA and DHA content, choose a fresh, well-tested product, and discuss higher doses with a clinician if you take blood thinners.
The takeaway
Omega-3 is not a miracle, and the DO-HEALTH ageing effect was measured in months, not years. But it is one of the rare supplements with randomised evidence for moving validated biological-ageing clocks, a validated blood biomarker to track your status, and a food-first path to get there. For longevity-minded professionals across Asia, the sensible play is to eat oily fish regularly, check your Omega-3 Index, top up with a quality EPA/DHA or algal supplement if you fall short, and treat omega-3 as one lever among several — most powerful when paired with vitamin D and strength training.