What is biological age, and can a test measure it?
A birthday gives you one number. Biological age is researchers’ attempt at a second one, built in more than one way.
Arun Verma, co-founder of Triangle · 2026-10-17
This is not clinical evidence and not medical advice. It does not replace your care team. Discuss anything here with your clinician before you act on it.
What is biological age, and can a test measure it?
Researchers use “biological age” for an estimate of how much damage, physiological change and loss of function a person’s cells have accumulated over time, as opposed to the years since birth. They estimate it in several ways, including patterns of DNA chemistry and sets of biomarkers. NIA describes epigenetic clocks, the DNA-based approach, as tools used by researchers. As researcher Morgan Levine puts it, biological age is often defined in one dimension, but aging itself is multidimensional. The two approaches start from different measurements: DNA methylation patterns in one case and biomarker levels in the other.
How is biological age different from chronological age?
Your birthdate gives your chronological age. Biological age is meant to describe the age your cells, tissues and organ systems appear to be, based on biochemistry, NIA explains. The two can differ. When a DNA methylation estimate of someone’s biological age comes out higher than their chronological age, researchers call it epigenetic age acceleration. NIA likens the epigenome, which is affected by environment and experiences over time, to the rings inside a tree, which record a tree’s age and where it met damage or stress.
How is a biological age built from biomarkers?
One approach compares you with an average. NIH Research Matters describes measuring a set of biomarkers and comparing them with what is typical for a given chronological age, using the general population as the reference. In the words of one researcher it quotes, your biomarker levels are lined up against the population average, and you “look about like a 55-year-old.” An NIA-funded researcher, Morgan Levine, used machine learning on big longitudinal studies, such as a CDC health survey, to pick out nine biomarkers that, combined with calendar age, were accurate predictors of future disease risk, functioning and mortality in those studies, NIA reports.
What is an epigenetic clock?
Epigenetic clocks estimate age from DNA methylation: chemical tags called methyl groups that attach at particular spots in DNA and can turn genes on or off. The tags sit on the DNA without changing its sequence, and they can change across a lifetime in response to environmental exposures. The NIA-funded study led by University of Michigan scientists used three types of clocks: first generation (Horvath and Hannum), second generation (GrimAge and PhenoAge) and third generation (DunedinPACE), with the second and third designed to improve on the earlier ones. DunedinPACE, NIH Research Matters says, was built to show how fast someone is aging rather than how much they have aged, using a New Zealand study of more than 1,000 people who had health evaluations between ages 26 and 45.
Do biological age estimates predict health outcomes?
In an NIA-funded study of more than 3,500 Americans age 51 and older, newer clocks were consistently associated with key aging health outcomes, though findings differed somewhat across clock types. Social and behavioral factors, such as demographics and health behaviors, remained stronger predictors than the clocks, with one exception NIA names: having multiple chronic diseases. When combined with other biomarkers, epigenetic age still predicted mortality and multiple chronic diseases, but could not predict functional difficulties or cognitive dysfunction. Earlier, a 2017 NIA report on a study of more than 13,000 people found that the gap between epigenetic age and chronological age predicted mortality risk independent of known risk factors, and it said more research is needed to understand epigenetic aging.
Can a test tell me my own biological age?
NIA describes epigenetic clocks as tools used by researchers, and the study it summarizes analyzed data from more than 3,500 people in the Health and Retirement Study. NIA’s 2024 write-up says the study’s findings suggest that along with traditional social and behavioral predictors of health, epigenetic age measures are a valuable tool for aging research and for predicting health outcomes later in life, and that further research may examine whether age-acceleration predictions differ within different population groups. A fair question for a clinician who knows your history is what any single number would mean for you.
What could I ask about a biological age score I have been given?
You could ask whoever provides a score which biomarkers or sample type it uses, which group of people it was compared with, and whether it has been tested in people of your age and background. MedlinePlus Genetics says patterns of epigenetic modification vary among individuals, in different tissues within an individual, and even in different cells within a tissue. Another question is which clock a score came from; in the NIA-funded study, findings differed somewhat across clock types. A fair question for a clinician is how the score sits next to the lab results you already have, and whether either bears on your care.
Where does the research stand?
NIH Research Matters describes work that measures the aging of individual organs from certain proteins in the blood, and notes that different organs can age at different rates, even in the same person. On epigenetic aging, NIA wrote in 2017 that more research is needed to understand the process and how it affects the contributors to mortality.
Sources
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says biological age refers to the accumulating damage, physiological changes and loss of function that occur in a person’s cells over time.
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says epigenetic clocks are tools used by researchers to quantify biological age using a set of biological markers, based on the concept that certain epigenetic modifications, such as DNA methylation patterns, change predictably over time in cells.
- NIA: The epigenetics of aging: What the body’s hands of time tell us (Research Highlight, March 26, 2021): NIA quotes researcher Morgan Levine as saying that a lot of times biological age is defined in one dimension, but aging itself is multidimensional.
- NIA: The epigenetics of aging: What the body’s hands of time tell us (Research Highlight, March 26, 2021): NIA says chronological age is based on a birthdate, while biological age means the true age that our cells, tissues and organ systems appear to be, based on biochemistry.
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says epigenetic age acceleration occurs when an estimate of a person’s DNAm-predicted biological age is higher than their chronological age.
- NIA: The epigenetics of aging: What the body’s hands of time tell us (Research Highlight, March 26, 2021): NIA says the epigenome is affected by our environment and experiences over time, similar to how rings inside a tree tell the tree’s age and mark where it encountered damage or stress.
- NIA: Research in Context: Can we slow aging? (reprint of NIH Research Matters, October 25, 2024): NIH Research Matters says one approach to aging clocks is to measure various biomarkers and compare them to what is typical for a given chronological age, using the general population as a reference, and quotes researcher Daniel Belsky describing how a person’s biomarker levels are lined up against the population average, so that “you look about like a 55-year-old” and are called biologically 55.
- NIA: The epigenetics of aging: What the body’s hands of time tell us (Research Highlight, March 26, 2021): NIA says NIA-funded researcher Morgan Levine used a machine learning approach to find patterns in big longitudinal studies like the CDC’s National Health and Nutrition Examination Survey to identify a set of nine biomarkers that were accurate predictors of future disease risk, functioning and mortality when combined with participants’ calendar ages.
- NHGRI: Talking Glossary of Genomic and Genetic Terms, Methylation: NHGRI says DNA methylation is a mark in which chemical tags called methyl groups attach at particular places on DNA, where they can turn genes on or off.
- NHGRI: Epigenomics Fact Sheet (last updated August 16, 2020): NHGRI says epigenomic marks do not change the sequence of the DNA; they change the way cells use the DNA’s instructions.
- NHGRI: Epigenomics Fact Sheet (last updated August 16, 2020): NHGRI says the epigenome can change throughout a person’s lifetime, and its modifications can be altered in response to environmental exposures.
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says the NIA-funded study, led by University of Michigan scientists, used three types of epigenetic clocks: first generation (Horvath and Hannum), second generation (GrimAge and PhenoAge) and third generation (DunedinPACE).
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says the second and third generation clocks were designed to improve on earlier clocks.
- NIA: Research in Context: Can we slow aging? (reprint of NIH Research Matters, October 25, 2024): NIH Research Matters says DunedinPACE was developed as an aging “speedometer” that shows how fast or slow someone is aging, as opposed to a clock that shows how much someone has aged, using the Dunedin Study, a long-term health study of more than 1,000 people born in New Zealand in 1972-73 whose participants received comprehensive health evaluations at four time points from ages 26 to 45.
- NIA: Research in Context: Can we slow aging? (reprint of NIH Research Matters, October 25, 2024): NIH Research Matters says different organs can age at different rates, even in the same person, and that researcher Tony Wyss-Coray has shown it is possible to measure the aging of individual organs based on levels of certain proteins in the blood.
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says its funded study analyzed data from more than 3,500 participants in the Health and Retirement Study, a nationally representative study of Americans age 51 and older.
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says the newer epigenetic age acceleration measures were consistently associated with key aging health outcomes, though findings differed somewhat across clock type.
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says social and behavioral factors remained stronger predictors of aging-related outcomes than epigenetic age acceleration measures, with one notable exception: multimorbidity, or having multiple chronic diseases; the factors it compares include demographics and health behaviors.
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says that when combined with other biomarkers, epigenetic age still predicted mortality and multimorbidity, but could not predict functional difficulties or cognitive dysfunction.
- NIA: Epigenetic age estimated by changes in DNA methylation predicts mortality (Research Highlight, January 19, 2017): NIA’s 2017 report says a study of more than 13,000 people in 13 population-based studies found that the difference between epigenetic age and chronological age predicted risk of mortality, independent of known mortality risk factors.
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says the study findings suggest that along with traditional social and behavioral predictors of health, epigenetic age measures are a valuable tool for aging research and predicting health outcomes later in life.
- NIA: Age estimated by changes to DNA can help predict health outcomes, mortality in older adults (Research Highlight, February 22, 2024): NIA says further research may examine whether age acceleration predictions differ within different population groups.
- MedlinePlus Genetics: What is epigenetics?: MedlinePlus Genetics says patterns of epigenetic modification vary among individuals, in different tissues within an individual, and even in different cells within a tissue.
- NIA: Epigenetic age estimated by changes in DNA methylation predicts mortality (Research Highlight, January 19, 2017): NIA’s 2017 report says more research is needed to better understand the process of epigenetic aging and how it affects the contributors to mortality.
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