Epigenetic Clocks and DNA Methylation in Aging
How epigenetic clocks estimate age from DNA methylation, which clocks exist, how reliable they are, and what trials show when diet or calorie intake is changed.
Content last updated . This page has not been medically reviewed.
Quick answer
An epigenetic clock is a research tool. It reads chemical tags on DNA (called DNA methylation) at a chosen set of sites and turns the pattern into a number, often reported in "years". [1] Some clocks track calendar age very closely, and some newer ones were built to predict illness or death. None of them is a diagnosis, and a change in a clock number is not the same as a change in health. This page explains what the clocks are, how they differ, and what the few intervention trials show.
How well do the clocks predict outcomes?
In cohort studies, clocks built to predict health outcomes were associated with later death, heart disease and cancer. [5] DunedinPACE was associated with illness, disability and death, with effect sizes similar to GrimAge. [6] These are associations at the group level in the authors' own cohorts. Label: promising but limited as a research tool; it does not show that a person's own number can guide any decision.How reliable is a single measurement?
Reliability is a real problem. One study found technical noise could produce differences of up to 9 years between replicate samples for six prominent clocks. [7] The same group proposed a computational fix that brought most replicates within 1.5 years. [7] A review of the field also lists key challenges in understanding how clocks work and how useful they are as biomarkers. [1]What do intervention trials show?
Changing a clock number is a biomarker result, not a health outcome.- Calorie restriction (CALERIE). In a post hoc analysis of a randomized trial, 220 adults without obesity were assigned to 25% calorie restriction or their usual diet for 2 years. [8] Restriction slowed DunedinPACE but did not significantly change age estimates from other clocks, including PhenoAge and GrimAge, and effect sizes were small. [8] The authors say that a conclusive test needs trials with long-term follow-up on healthy-aging endpoints. [8] Label: mixed.
- Diet and lifestyle pilot. A randomized pilot of 43 healthy men aged 50 to 72 tested an 8-week program that combined diet, sleep, exercise, relaxation, probiotics and phytonutrients against no intervention. [9] DNA-methylation age was 3.23 years lower than controls. [9] The program had many parts, the trial was small and short, and the authors call for larger and longer trials. [9] Label: insufficient evidence.
Neither trial measured whether participants lived longer or had fewer diseases.
Frequently asked questions
What is an epigenetic clock?
It is a formula applied to DNA methylation levels at selected sites to estimate age or the pace of aging. [1]
Can diet or lifestyle "reverse" an epigenetic clock?
A small pilot reported a lower methylation-age estimate after an 8-week multi-part program, and a larger calorie-restriction trial slowed one pace-of-aging measure but not other clocks. [9][8] Neither shows better health or longer life.
Are the test results consistent from one sample to the next?
Not always. Technical noise produced differences of up to 9 years between replicates in one study of six clocks. [7]
Does a "younger" clock number mean a longer life?
Clocks built to predict outcomes are associated with later illness and death across groups of people. [5][6] That is not proof that lowering your own number extends life.
Is an epigenetic age test a medical diagnosis?
No source we read supports using a clock to diagnose a condition or guide treatment. The authors of one review discuss ongoing challenges for biomarker use. [1]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: established (well replicated), promising but limited, mixed, insufficient evidence and marketing claim.
What DNA methylation is, in plain words
DNA methylation is a small chemical tag that can sit on DNA at places called CpG sites. Methylation patterns change as people age, and a clock is a set of CpG sites whose methylation levels together estimate age. [1] The first widely used multi-tissue clock used 353 CpG sites and was built from about 8,000 samples across 51 healthy tissues and cell types. [2]Clocks are not all the same
Different clocks were trained to predict different things, so they should not be treated as one measurement.| Clock | Built to predict | Notes from the sources |
|---|---|---|
| Horvath (2013) | Calendar age, across many tissues | Age acceleration was reported in all 20 cancer types studied, on average 36 years. [2] |
| Hannum (2013) | Aging rate in blood | Built from blood of 656 people aged 19 to 101. [3] |
| PhenoAge (2018) | A composite of clinical measures of "phenotypic age" | Reported to outperform earlier clocks for predicting outcomes including all-cause mortality. [4] |
| GrimAge (2019) | Time to death | Combines seven DNA-methylation estimates of blood proteins with an estimator of smoking pack-years. [5] |
| DunedinPACE (2022) | The pace of aging | Trained on change in 19 organ-system indicators across four time points over two decades in one birth cohort. [6] |
Two points follow from the table. First, GrimAge includes a smoking estimate, so part of what it predicts reflects smoking history. [5] Second, the pace-of-aging clock measures speed of change, not an age. [6]
Safety and limits
Reading a clock requires a blood or saliva sample, which carries little risk. The risks are indirect: false reassurance, unneeded anxiety, or buying products because of a number. Regulatory status of consumer epigenetic tests was not verified for this page. Do not change or stop any medicine because of a clock result, and talk with a clinician about concerns. For consumer tests see direct-to-consumer epigenetic age tests, for a side-by-side view see biological age clocks compared, and for general testing limits see biomarkers and biological age tests and interpreting test results without overinterpreting. Background on the concept is in biological age vs chronological age, and the framework behind it is in the hallmarks of aging. One of the interventions tested is covered in calorie restriction and aging research.
References
- Bell CG et al. DNA methylation aging clocks: challenges and recommendations. Genome Biology, 2019. Read 2026-10-22.
- Horvath S. DNA methylation age of human tissues and cell types. Genome Biology, 2013. Read 2026-10-22.
- Hannum G et al. Genome-wide methylation profiles reveal quantitative views of human aging rates. Molecular Cell, 2013. Read 2026-10-22.
- Levine ME et al. An epigenetic biomarker of aging for lifespan and healthspan. Aging, 2018. Read 2026-10-22.
- Lu AT et al. DNA methylation GrimAge strongly predicts lifespan and healthspan. Aging, 2019. Read 2026-10-22.
- Belsky DW et al. DunedinPACE, a DNA methylation biomarker of the pace of aging. eLife, 2022. Read 2026-10-22.
- Higgins-Chen AT et al. A computational solution for bolstering reliability of epigenetic clocks. Nature Aging, 2022. Read 2026-10-22.
- Waziry R et al. Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial. Nature Aging, 2023. Read 2026-10-22.
- Fitzgerald KN et al. Potential reversal of epigenetic age using a diet and lifestyle intervention: a pilot randomized clinical trial. Aging, 2021. Read 2026-10-22.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.