Omega-3, Vitamin D, Exercise: The Honest Read on 'Biological Age'

A patient walked into clinic this week holding her phone like it owed her money. "Doctor, my biological age came back as 56. I am 49. What do I do?"

I asked her what test she had taken, where, and what the report said her age was the year before. She had answers to one and a half of those three questions. Most people who order a biological age test do. The result lands in the inbox, the headline number lands in the chest, and very few of us know whether the test we just paid for actually tracks anything that matters, or what we are supposed to do about it on a Tuesday in Singapore.

I want to walk you through two pieces of evidence that came out of solid journals in the last 18 months and have quietly changed how I talk to patients about this. The first is the DO-HEALTH trial in Nature Aging, which tested whether a few simple, cheap interventions actually move the needle on DNA methylation-based biological age. The second is a systematic review and meta-analysis from the NUS Academy for Healthy Longevity, published in The Lancet Healthy Longevity, which looked at which biological age clock most reliably tracks frailty. Read together, they give the most useful answer we have to that patient question.

What a Biological Age Test Is Actually Measuring

When someone says "biological age" today, they usually mean a number generated from a DNA methylation pattern in your blood. The pattern is run through one of several published algorithms, called epigenetic clocks. The clocks come in roughly three generations.

The first generation, like the Horvath clock and the Hannum clock, was trained to predict your chronological age. They work, but they were never designed to track health. The second generation, like PhenoAge and GrimAge, was trained on actual mortality and clinical biomarkers. They are the ones that hold up best when researchers ask whether biological age predicts dying, frailty or disease. The third generation, like DunedinPACE, was trained in a longitudinal Dunedin cohort and gives a "pace of ageing" score rather than a fixed age. Below 1.0 means you are ageing slower than calendar time. Above 1.0 means you are ageing faster.

If your test only quoted you a Horvath number, what you have is a measure of how well the algorithm guesses your driver's licence date. That is not nothing, but it is not the same as a measure of how fast you are heading for a bad outcome.

The Singapore Meta-Analysis That Sorted the Clocks

In November 2025, a team led by Jian Hua Tay and Professor Andrea Maier at the NUS Academy for Healthy Longevity, working with collaborators in Porto and Amsterdam, published a systematic review and meta-analysis in The Lancet Healthy Longevity. They pooled 24 studies covering 28,325 participants, median age 65, more than half of them women, and asked a simple question. Of all the published clocks, which one most reliably tracks frailty, the most clinically meaningful end-point of unhealthy ageing?

The answer was clear. Across cross-sectional studies, higher GrimAge age acceleration showed the strongest association with frailty (standardised β 0.11, 95 per cent CI 0.06 to 0.15). PhenoAge acceleration came next, then Hannum, then DunedinPACE. The static "DNA methylation age" itself, the simple clock-on-the-wall version, showed no association with frailty.

Across longitudinal studies, only GrimAge held up as a predictor of worsening frailty over time. PhenoAge and pace of ageing did not, in this dataset.

What I take from this paper is not that the other clocks are useless. They tell us different things. But if you want a single number that tracks the bad direction we are trying to avoid, GrimAge is currently the one with the best evidence. When I read a patient's biological age report, GrimAge or DunedinPACE is the column I look at first.

Now to the Trial That Tested Three Real Interventions

Here is where the conversation usually breaks down. People want to know not whether the test is real, but what they should do if the number is high. Until recently, the honest answer was "we have observational data, but very little randomised evidence in humans". That changed in February 2025.

The DO-HEALTH trial, run across five European countries by Heike Bischoff-Ferrari and her group at the University of Zurich, randomised 2,157 community-dwelling adults aged 70 and older to a 2-by-2-by-2 factorial trial of three interventions. They received vitamin D 2,000 IU per day, or placebo. They received omega-3 fatty acids 1 gram per day, in a 1:2 EPA-to-DHA ratio, or placebo. They received a 30-minute home strength training programme three times per week, or a control programme of joint flexibility exercises. The interventions ran for three years.

The clinical results of DO-HEALTH were published in JAMA in 2020. None of the three interventions individually changed the six pre-specified primary outcomes of blood pressure, fractures, physical performance, cognition or infections at three years.

What changed in February 2025 was a post-hoc biological age analysis, published in Nature Aging. In a sub-cohort of 777 DO-HEALTH participants who had stored blood for DNA methylation analysis at baseline, year 1 and year 3, the team looked at four next-generation clocks: PhenoAge, GrimAge, GrimAge2 and DunedinPACE. They asked whether the three interventions, alone or in combination, slowed any of these clocks.

Three findings stood out.

One, omega-3 alone slowed three of the four clocks. PhenoAge, GrimAge2 and DunedinPACE all moved in the right direction in the omega-3 group versus placebo, with standardised effect sizes of 0.16 to 0.32 units, equivalent to 2.9 to 3.8 months of biological age slowed over three calendar years.

Two, vitamin D alone and exercise alone did not, on their own, move any of the four clocks. That is worth repeating. The home strength training programme, on its own, did not produce a measurable slowing of biological age in this trial.

Three, the three interventions stacked. When PhenoAge was the outcome, omega-3 plus vitamin D plus exercise produced an additive benefit larger than any one of them alone. The whole was larger than the parts.

This is not a magic-bullet trial and it is important not to read it as one. The effect sizes are modest. The 2.9 to 3.8 months of slowing over three years is real, but small. It is also a post-hoc analysis, which means we should treat it as hypothesis-generating rather than definitive. And the participants were generally healthy older adults aged 70 and above, with reasonable nutritional status to start with. Younger Singaporeans, sicker Singaporeans, and those at frank vitamin D or omega-3 deficiency may respond differently. Probably more, but we do not know yet.

Why the Result Is Still Useful in Singapore

Three things give this trial more local weight than the headline numbers suggest.

First, vitamin D deficiency is endemic here. The largest population-level Singapore data we have, a 2017 Nutrients study by Man and colleagues at the Singapore Eye Research Institute, examined 1,139 Chinese, Malay and Indian Singaporeans aged 40 to 80 and found suboptimal 25-hydroxyvitamin D in 76.1 per cent of the cohort. A separate 2016 PLOS ONE study by Bi and colleagues at the A*STAR Clinical Nutrition Research Centre, in 114 healthy adults, found about 42 per cent were frankly deficient (below 50 nmol/L). We are an equatorial country with one of the highest rates of vitamin D deficiency reported in Asia, mostly because we are an indoor, sunscreen-using, office-air-conditioned population. The DO-HEALTH participants started with much higher vitamin D status than that. If vitamin D is going to add to omega-3, it has the most room to do so in people who are deficient. That is most of us.

Second, omega-3 intake in our region is below the levels that moved the clocks. The DO-HEALTH dose of 1 gram of EPA plus DHA per day, in a 1:2 ratio, is achievable from food. Two servings per week of oily fish (salmon, mackerel, sardines, ikan kembong, ikan tenggiri) gets most adults to roughly that level on average. The EPA and DHA dose people get from a once-a-week white fish dish, or from fish balls and fishcake, is significantly lower than the trial dose, because both the species and the cooking method matter.

Third, the strength training arm is not a reason to skip strength training. The earlier JAMA paper from DO-HEALTH already established that the home programme was modest in dose, three 30-minute sessions per week of light resistance and balance work, and underpowered to show changes in functional outcomes alone in healthy 70-year-olds. The lifelong evidence base for strength training, captured in the Asian Working Group for Sarcopenia 2019 Consensus Update and its more recent 2025 revision, is overwhelming. The DO-HEALTH biological-age finding is not a finding that exercise does not work. It is a finding that this particular dose of light home exercise, alone, did not move four particular biological age clocks in three years. Those are different statements.

What I Now Tell Patients to Do

The DO-HEALTH trial does not change my advice on big-rock prevention. It refines it. Here is the version I am giving in clinic now.

1. Get to a 25-hydroxyvitamin D level above 75 nmol/L

If you have never had your vitamin D measured, do it once. The cost is modest and the prevalence of deficiency in Singapore makes the test high-yield. The clinical target most local endocrinologists agree on is 75 to 125 nmol/L (30 to 50 ng/mL) for adults. If you are below 50 nmol/L, you are deficient, and replacement under medical supervision is reasonable. The DO-HEALTH dose of 2,000 IU per day was safe across three years in older adults. Routine high-dose bolus vitamin D is not safe and increases falls and fracture risk in some studies.

2. Hit the omega-3 dose, ideally from food

The trial dose was 1 gram of EPA plus DHA per day, in a 1:2 ratio. In food, that is approximately two servings per week of oily fish, properly cooked. Salmon, mackerel, sardines, ikan kembong, ikan tenggiri, snapper, anchovies in modest portions. Fish balls and fishcake do not count for this purpose because the protein-to-flour-to-salt ratio is not what you want. If you cannot reliably eat fish twice a week, a low-dose omega-3 supplement at the trial dose is a reasonable substitute, but talk to your doctor first, particularly if you take warfarin, dabigatran, apixaban or rivaroxaban, or if you are about to have surgery. The bleeding signal from omega-3 at 1 gram is small but real and should be discussed.

3. Do strength training because it works for everything else

The DO-HEALTH biological-age data does not say "skip resistance training". The full body of evidence still says that resistance training two to three times per week reduces falls, fractures, all-cause mortality and dementia risk, and is one of the few interventions that can reverse sarcopenia. Pick your dose appropriately for age and joints. If you are 50 and reasonably fit, the dose is two full-body sessions a week, plus walking and one harder cardiovascular session. If you are 70 and starting fresh, three short home strength sessions a week is the DO-HEALTH protocol and a sensible floor.

4. Combine, do not pick

The most quietly important sentence in the DO-HEALTH paper is the one about additive effects. The treatments stacked. There was no winner. There was a combination. Patients who treat longevity as a single-pill question (the right supplement, the right exercise, the right diet) tend to underperform patients who treat it as a stacked, boring set of habits run for years.

Where Biological Age Testing Actually Helps

Should every adult test their biological age? No. The clocks are useful in two specific situations.

The first is when someone is highly motivated, has the basics already in place (good sleep, no smoking, reasonable weight, regular movement), and wants an objective marker to track over time. In that case a baseline GrimAge or DunedinPACE, repeated annually, is a reasonable feedback loop. It is more meaningful than chasing a single LDL number every six months.

The second is when there is a clinical question that the standard panel cannot answer. For example, a 55-year-old with normal lipids, normal blood sugar, normal blood pressure, but a strong family history of early heart disease and a stressful decade behind them. The standard clinic markers say "low risk". A biological age clock that is significantly above their chronological age says "look harder", and may justify more advanced imaging or earlier intervention.

For everyone else, the highest-yield investments are the boring ones. Sleep. Strength. Steps. Salt and sugar restraint. Two fish meals a week. A vitamin D level you actually know. The clocks are a feedback tool, not a north star.

The Bottom Line

The DO-HEALTH trial is the cleanest randomised data we have on whether everyday interventions can slow biological age. Omega-3 at 1 gram per day moved three of four clocks. Vitamin D and home strength training did not move them alone, but added to omega-3 made the effect larger. The NUS-led Lancet Healthy Longevity meta-analysis tells us the clock most worth watching, if you watch one, is GrimAge. The whole effect, even at three years, is modest, in months not decades. The honest read is that biological age testing is more useful as a feedback tool than as an oracle, and the interventions that move it are the same boring ones that move every other longevity outcome.

My patient with the GrimAge of 56 in a 49-year-old body went home with a 25-hydroxyvitamin D test, two scheduled fish meals a week, a referral for a structured strength programme at a local gym, and a follow-up plan in twelve months. Not a panic. Not a supplement stack. A short list of things she would have been told to do anyway, with one more reason to do them.

That is what a useful biological age test looks like in practice. Not a verdict. A nudge in the direction the rest of the evidence already points.

References

1. Bischoff-Ferrari HA, Gängler S, Wieczorek M, Belsky DW, Ryan J, Kressig RW, 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;5(3):376-385. DOI: 10.1038/s43587-024-00793-y
2. Tay JH, Barros D, Wang W, Wazny VK, Maier AB. Biological age measured by DNA methylation clocks and frailty: a systematic review and meta-analysis. The Lancet Healthy Longevity. 2025;6(10):100773. DOI: 10.1016/j.lanhl.2025.100773
3. Bischoff-Ferrari HA, Vellas B, Rizzoli R, Kressig RW, da Silva JAP, Blauth M, et al. Effect of Vitamin D Supplementation, Omega-3 Fatty Acid Supplementation, or a Strength-Training Exercise Program on Clinical Outcomes in Older Adults: The DO-HEALTH Randomized Clinical Trial. JAMA. 2020;324(18):1855-1868. DOI: 10.1001/jama.2020.16909
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