GrimAge is a second-generation epigenetic clock that estimates mortality risk from DNA methylation in blood and reports the result as an age in years. It was developed by Ake Lu, Steve Horvath and colleagues and published in 2019, and the name is a reference to the grim reaper. Unlike the first clocks, it was never trained to guess your calendar age. It was trained against time to death, which is why its reading tracks smoking, disease and survival more closely than it tracks your birthday.
What it measures
The input is an ordinary blood sample. Like every Epigenetic clock, it reads DNA methylation — the chemical tags that sit on the DNA — at a defined set of sites and feeds that pattern into an algorithm. What separates this one is how the algorithm was assembled.
It was built in two stages. First the authors trained methylation-based stand-ins for seven plasma proteins linked to aging and disease — adrenomedullin, beta-2-microglobulin, cystatin C, GDF-15, leptin, PAI-1 and TIMP-1 — plus a methylation estimate of smoking history in pack-years. Then those surrogates, together with chronological age and sex, were fitted against time to death in a long-running cohort. The resulting mortality risk score was rescaled into years so it could be compared with a calendar age. A later revision, GrimAge2, added methylation surrogates for C-reactive protein and hemoglobin A1c.
Two things follow from that design. The score is not a pure methylation reading, since age and sex go in as inputs, and smoking carries real weight inside it.
Typical values
A report from GrimAge — the epigenetic clock of mortality usually arrives in one of these forms.
| Output | Unit | How to read it |
|---|---|---|
| DNAm GrimAge | Years | Set against your calendar age |
| GrimAge acceleration | Years, plus or minus | What is left after calendar age is accounted for; by construction it sits around zero in the reference group, and positive means older than expected |
| GrimAge2 | Years | The revised model; its numbers are not interchangeable with the original |
There is no normal range, no clinical cut-off and no threshold that means anything on its own. Values shift with the model version, the array, the laboratory and how the sample was handled. Compare a result only against your own earlier readings from the same provider and the same version of the test.
Why it matters for longevity
In cohort studies, higher GrimAge acceleration is associated with earlier death, with coronary heart disease and cancer, with faster cognitive decline, and with fewer years lived free of chronic illness. It has generally predicted mortality better than the first-generation clocks trained on calendar age, which is why researchers reach for it when the question is risk.
The limits are worth stating plainly. These are observational associations, not proof that the biology it reads causes the outcomes, and part of the predictive power comes from inputs already known to shorten life, above all smoking. Nobody has shown that lowering the number extends life. It remains a research instrument and a risk marker; no regulator treats it as a diagnostic test.
What changes it
Smoking moves it more than anything else you control, because pack-year history is an explicit component: current smokers show markedly higher acceleration than never-smokers, and former smokers sit between the two. Obesity, heavy alcohol intake, physical inactivity and long-running social and economic disadvantage all travel with a higher reading. Regular activity, higher aerobic fitness and a diet built on plants, fish, legumes and whole grains travel with a lower one. Chronological age and sex are model inputs, so nothing you do touches them.
Trial evidence is thin and early. In DO-HEALTH, daily omega-3 slowed several second-generation clocks, a GrimAge version among them. A small pilot of six months of endurance cycling reported a slowdown alongside a large gain in aerobic fitness. Clocks also disagree: in the CALERIE calorie-restriction trial the effect showed up on the pace-of-aging clock rather than on this one. Effect sizes have been modest, and what they mean for how long people live is unknown. Acute illness can shift a reading too, so retest before acting on a surprise.
Related reading
- Epigenetic Clocks: Measuring Age from DNA
- What Biological Age Is and How to Measure It
- Aerobic Training Slowed the Epigenetic Clock
- Omega-3 Slowed Biological Aging in the DO-HEALTH Trial
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.