A daily capsule shaved about 3 months off body age blood tests, trial finds

Birthdays count years, but two people of 75 can seem very different. One climbs stairs with ease and the other struggles. Scientists have built blood tests that try to capture that gap by guessing how old a body seems, rather than how long it has been alive [1].

A new look at a large European trial used those tests on older adults who took vitamin D, omega-3 capsules or a home exercise program for three years. Omega-3 moved the tests the most, by about 3 to 4 months of body age over the three years [1].

That change is small, and it is a score on a test, not a longer or healthier life. The question was also asked after the trial ended, using stored blood, which leaves more room for chance [1].

The work was led by Heike Bischoff-Ferrari of the University of Zurich and published in Nature Aging in 2025. The Swiss National Science Foundation paid for the DNA tests. The wider trial had money from the European Union, among others [1].

What was the trial?

The trial, called DO-HEALTH, signed up 2,157 adults aged 70 or older in Switzerland, France, Germany, Austria and Portugal. They lived at home, could get around on their own, and had no major illness in the five years before [2][3].

Chance, like a coin flip, put each person into one of eight groups, so every mix of three things was tested. The first was a daily vitamin D capsule. The second was a daily omega-3 capsule, a kind of fat like those in oily fish, made here from tiny sea plants called algae. The third was a home strength program three times a week [1][2].

People who did not get a real capsule got a placebo, a fake capsule with nothing active in it. People who did not get the strength program did stretching instead. Nobody knew which capsules they had [1][2].

The main results came out in JAMA in 2020. Nearly 9 in 10 people finished, but none of the three things made a clear difference to blood pressure, broken bones, infections, thinking skills or how well people moved. The authors put it this way:

These findings do not support the effectiveness of these 3 interventions for these clinical outcomes.

In plain words, on the health questions the trial was built to answer, nothing worked better than the fake capsules or the stretching. The new paper does not change that answer. It asks a different question of some of the same people [1][2].

How does a DNA age test work?

Every cell holds DNA, a long set of instructions for the body. Tiny chemical marks sit on top of it and help decide which instructions are switched on. The pattern of marks shifts as people get older, and computer programs can read that pattern from a blood sample to guess body age. These programs are called epigenetic clocks, after the marks that sit on top of DNA [1].

The team looked mainly at four newer clocks, called PhenoAge, GrimAge, GrimAge2 and DunedinPACE. These were built to line up with health and death records, not just birthdays. DunedinPACE works more like a speedometer, guessing how fast the body is aging right now [1].

Only Swiss volunteers were part of this check. Of 1,006 Swiss people in the trial, 777 had good blood samples from the start and the end of year three. Their average age was about 75, and about 6 in 10 were women. The lab that ran the tests did not know who was in which group [1].

Omega-3 on its own moved three of the four newer clocks, PhenoAge, GrimAge2 and DunedinPACE. Vitamin D and exercise on their own moved none. On PhenoAge only, all three together did slightly better than omega-3 alone. Two older clocks showed no change from anything [1]. The authors summed it up:

In summary, our trial indicates a small protective effect of omega-3 treatment on slowing biological aging over 3 years across several clocks, with an additive protective effect of omega-3, vitamin D and exercise based on PhenoAge.

In plain words, omega-3 nudged several clocks a little, and all three together nudged one clock a little more. On the speedometer clock, the change was about one percent slower aging. A different trial, where people ate fewer calories, saw a change about two to three times bigger on the same clock [1].

There are other reasons for care. The blood was read only twice, at the start and the end, which adds error. The Swiss group started with lower omega-3 levels than the trial as a whole, which the authors link to Switzerland having no sea coast. So the capsule may look stronger here than elsewhere. And one author helped build the GrimAge clocks, founded a nonprofit that licenses patents on some of them, and works for a company that studies aging. The paper says so openly [1].

This study does not show that omega-3 helps anyone live longer or stay healthier, and the authors say it is unknown whether the clock changes matter for long term health. What it does show is that, in healthy older Swiss adults, a daily omega-3 capsule moved several body age tests by a few months over three years. Blood saved from other years and countries could now test whether that holds up [1].