Omega-3, Vitamin D and Exercise: The DO-HEALTH Trial That Slowed Biological Aging in Older Adults

Long before anyone measured DNA, fishing families in northern Europe had a trusted remedy: a spoonful of cod liver oil. On Norway’s Lofoten Islands, the old center of the cod fishery, fishermen made the oil themselves by letting cod livers break down and then heating what was left. By the 1840s European doctors were writing about it, and in 1922 scientists identified its vitamin D. Later research showed the oil is also rich in omega-3 fats.

Halfway around the world, Japan offers a similar lesson. Fish has long been a daily food there, and the Japanese have higher omega-3 intakes and blood levels than people in most countries. They are also among the longest-lived people on Earth. One doesn’t prove the other, but the overlap is hard to ignore.

In February 2025, a large Swiss study added a modern chapter to this story. In Nature Aging, Professor Heike Bischoff-Ferrari and her colleagues reported that older adults who took a daily omega-3 supplement for three years showed slower “biological aging” on several epigenetic clocks. Adding vitamin D and a simple home strength routine boosted the benefit on one clock. Here is what the trial found, what it didn’t, and how to bring these habits into your week.

Key Takeaways

• In the DO-HEALTH trial, 777 Swiss adults aged 70 and older who took 1 gram of algae-based omega-3 daily showed slower aging on three of four epigenetic clocks over three years. The difference worked out to roughly three to four months.
• On one clock, called PhenoAge, omega-3, vitamin D (2,000 IU a day) and 30 minutes of home strength exercise three times a week added up. Together they worked better than any one of them alone.
• Vitamin D and exercise alone did not change any clock; they helped only in combination.
• Fatty fish, algae, flax, chia and walnuts, along with sensible sun exposure and regular strength work, are the food and lifestyle versions of these three habits.
• These are early, encouraging results. They measure biological aging markers, not lifespan or disease.

What Is “Biological Age,” and How Do You Measure It?

Your birth certificate gives your chronological age, but your cells keep their own record. As we age, chemical tags called methyl groups build up on DNA or fall away in predictable patterns. This is DNA methylation, and it helps switch genes on and off. “Epigenetic clocks” read these patterns from a blood sample to estimate how old your body seems at the cellular level.

Newer clocks were trained on health markers and the risk of illness and death, not just birthdays. DO-HEALTH used four of the best-validated: PhenoAge, GrimAge, GrimAge2 and DunedinPACE. DunedinPACE works like a speedometer, estimating how fast you are aging right now. As Bischoff-Ferrari notes, there is still no gold standard for measuring biological age, so the clocks are useful tools rather than the final word.

Inside the DO-HEALTH Trial

DO-HEALTH is one of Europe’s largest healthy-aging trials. It enrolled 2,157 people aged 70 and older in Switzerland, Germany, France, Austria and Portugal. All were reasonably healthy at the start. They were randomly placed into eight groups testing three habits, alone and in every combination:

• Omega-3: 1 gram a day from marine algae, about 330 mg EPA and 660 mg DHA
• Vitamin D3: 2,000 IU a day, well above the usual 800 IU recommendation for this age group
• Home strength exercise: about 30 minutes, three times a week, compared with a gentle flexibility routine

For the epigenetic study, the researchers analyzed blood samples from 777 Swiss participants. Their average age was about 75, and about 60% were women.

What They Found

Omega-3 was the standout. People taking it showed slower aging on three of the four clocks: PhenoAge, GrimAge2 and DunedinPACE. The researchers estimated the benefit at roughly 2.9 to 3.8 months of aging saved over three years. On DunedinPACE, the speedometer clock, omega-3 slowed the pace of aging by about 1%. The effect held regardless of sex, age or body weight. An exploratory analysis hinted that people who started with lower omega-3 levels may have benefited more.

The most interesting result was teamwork. On the PhenoAge clock, the three habits had additive benefits. Combinations that included omega-3 showed larger effects, and combining all three was more effective still, even though vitamin D or exercise alone did not move any clock. The authors suggest the three work through complementary pathways, which fits a whole-body view of health.

An Honest Look at the Limits

The epigenetic results come from a follow-up analysis that wasn’t planned at the start, with blood tested at only two time points. The Swiss volunteers were healthier and more active than many people their age. The main 2020 trial also found no significant benefit on its main clinical outcomes. Longer studies are needed to learn whether slower clocks mean fewer illnesses and longer lives, though the authors argue these limits would more likely hide a real effect than create a false one.

Omega-3s From Food: Fish, Algae, Flax and Walnuts

The omega-3 in DO-HEALTH came from algae, the original source of the omega-3s that build up in fish. For most people, the traditional route is still the tastiest:

• Cold-water fatty fish: salmon, mackerel, herring, sardines and tuna are rich in EPA and DHA, the forms used in the trial.
• Algae oil: a vegetarian and vegan source of EPA and DHA, and the same kind of source the trial used.
• Plant seeds and nuts: flaxseed, chia seeds and walnuts provide ALA, a plant omega-3. The body converts only small amounts of ALA into EPA and DHA. They’re still valuable (see our look at nuts and a longer life), but pair them with fish or algae.

Whole fish also brings protein and vitamin D along with its fats. We covered the “food over fish oil” view in a recent natural health news roundup on diets that slow aging.

Vitamin D: The Sunshine Nutrient

Your skin makes vitamin D in sunlight, but it makes less as we age, and northern latitudes, darker skin and sunscreen reduce it further. In DO-HEALTH, about a third of participants started below 20 ng/mL.

Food sources include salmon (a 3-ounce serving has about 570 IU), sardines, herring, egg yolks and fortified milk. For a balanced view of how to enjoy the sun safely, see our guide to sunlight’s benefits, risks and balance.

Simple Strength: The Third Piece

The DO-HEALTH exercise program wasn’t a gym membership. It was a simple home strength routine of about 30 minutes, three times a week. Alone it didn’t change the clocks, but as part of the trio it contributed to the PhenoAge benefit. Research also suggests 30 to 60 minutes of strength training a week may be a sweet spot for longevity.

How to Bring the DO-HEALTH Trio Into Your Week

1. Eat fatty fish twice a week. Try baked salmon, sardines on toast, or pickled herring the Nordic way. Non-fish eaters can choose algae oil.
2. Add a daily plant omega-3. Stir a tablespoon of ground flaxseed or chia into oatmeal or yogurt, or snack on a small handful of walnuts.
3. Get gentle, regular sunlight. Walk outdoors most days with face and arms briefly exposed, without burning. In winter, food and supplements matter more.
4. Know your vitamin D level. A blood test shows where you stand. The trial used 2,000 IU a day, below the 4,000 IU adult upper limit.
5. Do 30 minutes of home strength work three times a week. Chair sit-to-stands, wall push-ups, heel raises and light hand weights are a great start. Short bursts count too; see our post on exercise snacks.
6. Stack the habits. A sardine lunch, a sunny walk and a quick strength session cover all three in one day.

The Bottom Line

The DO-HEALTH findings give scientific support to wisdom our ancestors practiced: eat from the sea, get out in the sun, and keep your body strong. In adults over 70, a daily gram of omega-3 slowed several epigenetic aging clocks by a few months over three years. Adding vitamin D and simple strength exercise boosted the benefit on one clock. These are early findings about aging markers, not proof of a longer life, but the habits are affordable, traditional and good for the whole body.

Frequently Asked Questions

Do I need supplements, or can I get omega-3 from food?

The trial tested a supplement, so we can’t say for sure that food gives the same epigenetic result. Fatty fish is the richest whole-food source of EPA and DHA, though, and eating it twice a week is a long-standing tradition in many of the world’s healthiest cultures. Algae oil is an option for people who don’t eat fish.

Are flaxseed and walnuts enough on their own?

They provide ALA, a plant omega-3 with its own benefits. The body turns only small amounts of ALA into the EPA and DHA used in the trial, so plant eaters may want to add an algae source.

Is cod liver oil a good way to follow this approach?

Cod liver oil supplies both omega-3s and vitamin D, which is why it was so prized in northern traditions. It wasn’t what DO-HEALTH tested, and it also contains vitamin A, so read the label and count it along with any other supplements you take.

Does this mean omega-3 will make me live longer?

Not necessarily. The trial measured epigenetic clocks, not lifespan. The clocks are linked to health and survival, and large observational studies tie higher omega-3 levels to lower death rates. Longer trials are needed to confirm a direct effect on lifespan.

Safety note: High doses of omega-3 can affect bleeding, especially with blood thinners such as warfarin, and vitamin D above 4,000 IU a day is not advised without testing. If you take prescription medicines, check with your practitioner before adding supplements.

Sources

• Bischoff-Ferrari HA et al. Individual and additive effects of vitamin D, omega-3 and exercise on DNA methylation clocks of biological aging in older adults from the DO-HEALTH trial. Nature Aging, 2025 (full text, PMC)
• University of Zurich news release: Omega-3s can slow down aging process (February 2025)
• Bischoff-Ferrari HA et al. Effect of vitamin D, omega-3, or a strength-training exercise program on clinical outcomes in older adults: the DO-HEALTH randomized clinical trial. JAMA, 2020
• News-Medical: People with a higher Omega-3 Index lived longer (FORCE Consortium, Nature Communications, 2021)
• Science History Institute: The Man with a Fish on His Back (history of cod liver oil)
• NIH Office of Dietary Supplements: Omega-3 Fatty Acids fact sheet
• Clemson Cooperative Extension: Vitamin D fact sheet

This article is for educational purposes and is not a substitute for personalized advice from a qualified health practitioner.