Aging is a set of cellular processes that build up together, and a decade or more of life expectancy tracks with a short list of ordinary habits: not smoking, cardiorespiratory fitness, a healthy weight, regular movement and a good diet. Around that biology sits a fast-growing market of aging-clock tests and anti-aging supplements. The clocks are solid population science: people whose clock reads old are, on average, more likely to fall ill or die in follow-up.
No single clock has been shown to mean one person lives longer when the reading falls, different clocks disagree on the same blood sample, and the anti-aging drugs are tested mostly in animals or tiny human pilots. This page separates the biology that is settled from the claims that are not.
Findings & Outcomes
Aging is a biological process, and the research is advancing fast. The consumer version of it, the clocks, the supplements, the drugs taken off-label, is far ahead of what has been shown to help a person live longer.
What Aging Is
Aging is not a single process. It is a set of cellular and molecular changes that build up together and reinforce each other. At the tissue level this shows up as slower repair, a growing load of damaged cells the body no longer clears, and a low, steady background of inflammation that rises with the years, sometimes called inflammaging. Many processes change at once, which is why any single intervention has a limited ceiling.
No single treatment resets the whole system, and changing one process tends to affect the others, for better and worse. Much of what follows works through mechanisms covered elsewhere on this site: mitochondria, the recycling process of autophagy, and the controlled-stress pattern of hormesis.
The Hallmarks
Most researchers now organize aging around the hallmarks of aging. A 2013 review named nine, and a 2023 update expanded the set to twelve shared processes:
- genomic instability, accumulating DNA damage
- telomere attrition, the shortening of chromosome end-caps
- epigenetic alterations, drift in the chemical marks that control what a cell is
- loss of proteostasis, failing protein quality control
- disabled macroautophagy, weaker cellular recycling
- deregulated nutrient sensing
- mitochondrial dysfunction
- cellular senescence, the build-up of worn-out cells that will not divide or die
- stem cell exhaustion
- altered intercellular communication, including chronic inflammation
- dysbiosis, a disordered gut microbial community
The list is a framework for organizing the biology, not a proven chain of cause and effect. The hallmarks are tangled together and reinforce each other, so no one of them can be named the single root cause.
Chronological Versus Biological Age
Chronological age is the simple count from your birth date. Biological age is an estimate of your body's condition, built from measurable markers, and the two can differ. Two people born the same week can sit years apart on the cellular measures. Someone aging faster than the calendar carries more disease risk; someone aging slower carries less. That gap is what biological-age measures try to capture.
Biological age has to be inferred from proxies; there is no single measurement that reads it directly. The best-known proxy is the pattern of chemical tags on DNA, which is what the aging clocks read.
Aging Clocks
The epigenetic clock reads DNA methylation, small chemical tags on the genome, at a few hundred sites and fits them mathematically to age. The 2013 method fitted methylation at 353 sites and estimated a person's age across most tissues to within a median of about 3.6 years. That is what a biological-age test measures: a statistical model of your calendar age, and the gap between the estimate and the truth.
The important finding is at the population level. People whose clock reads older than their birthday are, on average, more likely to die in follow-up. Later clocks, GrimAge and DunedinPACE, were built to predict health outcomes directly, and they predict mortality, heart disease and disability better still.
A clock is validated as a predictor across thousands of people, not as a target proven to add years to any one life when the reading falls.
The marketing claims run ahead of this. The most cited age-reversal result comes from a study of nine men with no control group, in which four clocks read about 1.5 years younger after a year. With nine participants and no control, it is a hypothesis, and it cannot separate a change from ordinary variation or regression to the mean. Different clocks also disagree on the same sample. When CALERIE, the main human trial of eating less, applied a methylation panel, one pace-of-aging measure (DunedinPACE) slowed slightly while three age clocks (Horvath, Hannum, PhenoAge) did not move, on the same blood samples. A consumer test rests on one noisy reading, and the "reverse your age" claims attached to these clocks are not established in humans.
What slows aging
The strongest evidence for a longer, healthier life points to ordinary habits. In two large US cohorts followed for decades, adults who did not smoke, kept a healthy weight, moved regularly, drank moderately and ate well had a projected life expectancy at 50 about 12 years longer for men and 14 years longer for women than those with none of the five. Cardiorespiratory fitness shows one of the steepest associations in the literature: pooling 33 studies and 102,980 people, each 1-MET increment in fitness tracked with about 13% lower all-cause mortality and 15% fewer cardiovascular events, with no clear ceiling.
These habits act on the same hallmarks the drugs target:
- Exercise improves mitochondrial function and prompts autophagy.
- Keeping muscle counters the tissue loss that marks aging.
- Not smoking removes a direct source of genomic damage.
- Sleep and a good diet act on nutrient sensing and inflammation.
Almost all of this evidence is observational. It shows what travels with slower aging, not what causes it, and the habits cluster with education, income and access to care, which lengthen life on their own. The direction is consistent across studies; the exact number of years any single habit adds is not something an observational design can settle.
The Anti-Aging Drugs And Supplements
The drugs and supplements sold as anti-aging are mostly early-stage, tested in animals or small pilots of cellular markers. Caloric restriction, eating fewer calories without going short on nutrients, is the most reproducible lifespan-extending intervention in laboratory biology, working from yeast to mice, and in rhesus monkeys it delayed age-related disease. In people, the largest controlled trial, CALERIE, randomized 218 healthy adults to cut intake (about 12% in practice) and improved LDL cholesterol, blood pressure, C-reactive protein and insulin sensitivity over two years. It measured risk markers, not lifespan, and its aging-clock result was the small, split signal described above.
The individual molecules are earlier still:
- Rapamycin extends lifespan in mice even when started late in life, repeatably and in both sexes. In people it is an immunosuppressant with side effects and has not been shown to lengthen healthy life.
- Metformin has a mechanistic and epidemiological case now being tested in the TAME trial, which has not reported an anti-aging outcome.
- Senolytics, which clear senescent cells, have reached people only in tiny pilots: a short course of dasatinib plus quercetin lowered senescent-cell markers in nine people, with no control group and no health outcome measured.
- NAD precursors such as NMN raise NAD levels in small human studies without a shown effect on aging.
All are still in trials for slowing aging in a healthy person, whatever the marketing implies, and this page gives no dosing.
The findings below are graded unevenly by design. Many are marked animal or mechanistic, because
no trial can assign a person to a different rate of aging. The clock findings are graded on
prediction: they forecast risk across populations, and their caveats mark the distance between
forecasting a group and giving an individual a target to act on.
The Research & Studies
Everything here is based on the research we have collected and checked, sorted into groups and ordered with the strongest evidence first. Click any claim to open the studies behind it.
Longevity And Mortality
Eating less extends lifespan from yeast to mice and delays disease in monkeys
Eating fewer calories without malnutrition extends lifespan across many species and delayed age-related disease in monkeys.
Caloric restriction is the most reproducible lifespan-extending intervention in laboratory biology, working from yeast to worms to mice. In rhesus monkeys, long-running studies found reduced age-related deaths and delayed diabetes, cancer and cardiovascular disease, though design differences between two centers affected the all-cause mortality signal.
Who this may not transfer to:Measured in laboratory animals and monkeys; an effect on human lifespan is not established.
The studies · 3
Colman 2009, Science · Science
Colman 2014, Nature Communications · Nat Commun
Mattison 2017, Nature Communications · Nat Commun
Rapamycin extended lifespan in mice even when started late in life
Rapamycin extends lifespan in mice even when started late in life, but it is an immunosuppressant not shown to lengthen healthy human life.
In genetically heterogeneous mice, rapamycin fed from 600 days of age extended median and maximal lifespan in both sexes. The result is real and repeatable in mice. In people rapamycin is used as an immunosuppressant with side effects and has not been shown to extend healthy lifespan.
Who this may not transfer to:Measured in mice; a healthy-human lifespan effect is not established.
The study · 1
Harrison 2009, Nature · Nature
Five healthy habits added about 12 years for men and 14 for women
Adults with five basic healthy habits lived roughly a decade or more longer than those with none in two large cohorts.
Following two large US cohorts for decades, adults who did not smoke, kept a healthy weight, were physically active, drank moderately and ate well had a projected life expectancy at 50 about 12 years longer for men and 14 years longer for women than those with none of the five. The design is observational.
The study · 1
Li 2018, Circulation · Circulation
Progress Markers
Each 1-MET fitter tracks with about 13% lower death rate
Higher cardiorespiratory fitness tracks with a large drop in death rate, one of the steepest signals in the whole literature.
A meta-analysis pooling 33 studies and 102,980 participants found each 1-MET increment in cardiorespiratory fitness was associated with roughly 13% lower all-cause mortality and 15% lower cardiovascular events, with no clear ceiling. The underlying studies are observational, so the finding shows what travels with lower mortality and does not prove cause.
The study · 1
Kodama 2009, JAMA · JAMA
GrimAge and DunedinPACE predict death across groups, a marker not a target
Clocks built to track health, such as GrimAge and DunedinPACE, predict who is more likely to die or develop disease across large groups.
GrimAge, trained on plasma markers and smoking history, predicted time to death and to cardiovascular disease across several cohorts. DunedinPACE, derived from a single birth cohort followed for decades, estimates the pace of aging per year and tracks morbidity and mortality. Both are validated as population predictors; neither has been shown to be a target that changes an individual outcome when the number moves.
The studies · 2
Lu 2019, Aging · Aging (Albany NY)
Belsky 2022, eLife · eLife
Cutting calories slowed one pace-of-aging clock, the age clocks did not, in CALERIE
In the main human calorie-restriction trial, one pace-of-aging measure slowed slightly while three age clocks did not move on the same blood samples.
The CALERIE randomized trial applied a methylation panel to participants who cut intake for two years. DunedinPACE, the rate measure, slowed modestly, while the Horvath, Hannum and PhenoAge clocks showed no clear change. The measures disagreeing on the same samples shows how fragile a single clock reading is.
The study · 1
Waziry 2023, Nature Aging · Nat Aging
How it works
Methylation clocks estimate age to within about 3.6 years
An epigenetic clock reads chemical tags on DNA and estimates a person's calendar age to within a few years across most tissues.
The 2013 method fitted DNA methylation at 353 sites to chronological age across many human tissues, estimating age with a median error near 3.6 years. This is a statistical model of calendar age, and the gap between the estimate and true age is what a biological-age reading reports.
The study · 1
Horvath 2013, Genome Biology · Genome Biol
Aging mapped as twelve interacting hallmarks, a framework not a cause
Researchers organize aging into a short list of shared cellular changes called the hallmarks, twelve in the current version.
The 2013 review named nine hallmarks and the 2023 update expanded the set to twelve: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, disabled macroautophagy, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, chronic inflammation and dysbiosis. The framework organizes evidence, and because the hallmarks interact and reinforce each other, no one of them can be named the single root cause.
Who this may not transfer to:A framework for organizing evidence, not a measurement taken in people.
The studies · 2
Lopez-Otin 2013, Cell · Cell
Lopez-Otin 2023, Cell · Cell
A senolytic pilot lowered senescent-cell markers in nine people, not health outcomes
An early human pilot found a senolytic drug combination lowered markers of senescent cells, a surrogate rather than a health outcome.
In a small open-label pilot, a short course of dasatinib plus quercetin reduced several markers of senescent cell burden in blood and tissue. The study had nine participants and no control group, and it measured cellular markers, not disease or lifespan outcomes.
Who this may not transfer to:The trial did not report or analyze results by sex, so how far the finding differs between women and men is not established here.
The study · 1
Hickson 2019, EBioMedicine · EBioMedicine
Cholesterol And Lipids
A 12% calorie cut improved cholesterol, blood pressure and insulin over 2 years
Healthy adults who cut calories for two years improved cholesterol, blood pressure and insulin sensitivity, all risk markers rather than measured lifespan.
CALERIE randomized 218 healthy non-obese adults to a 25% intake cut or usual diet. They achieved about 12% in practice and improved LDL cholesterol, blood pressure, C-reactive protein and insulin sensitivity over two years. The trial measured risk markers, not survival.
The study · 1
Kraus 2019, Lancet Diabetes Endocrinol · Lancet Diabetes Endocrinol
Evidence And Methods
Clocks read about 1.5 years younger in nine men, with no control group
The most cited age-reversal result comes from nine men with no control group, so it reads as a hypothesis rather than a demonstration.
In a one-year open-label study of nine men taking growth hormone with two other drugs, four epigenetic clocks read about 1.5 years younger on average by the end. With no control group and nine participants, the design cannot separate a true change from ordinary variation or regression to the mean.
Who this may not transfer to:Measured only in men aged 51 to 65; whether it applies to women or other ages is untested.
The study · 1
Fahy 2019, Aging Cell · Aging Cell
Go Deeper
The biology this page describes acts through processes covered in their own right, and the levers that actually track with slower aging have their own pages:
- Mitochondria and energy and autophagy, two of the hallmarks you can influence, and hormesis, the controlled-stress principle underneath much of what helps.
- Muscle as an organ, because holding onto muscle and strength is one of the clearest markers of aging well, built by resistance training and fed by protein and muscle.
- Zone 2 training and VO2 max training, which build the cardiorespiratory fitness with the steepest link to living longer, and walking, the low-friction version most people will actually do.
Common Questions
What is the difference between biological and chronological age?
Chronological age is how long you have been alive. Biological age is an estimate of the state of your body, from markers such as DNA methylation, that can run ahead of or behind your calendar age. The gap predicts health and mortality across large groups. It does not yet tell an individual what to do: the clocks are validated as population predictors, not as targets shown to change your future when the number moves.
What are the hallmarks of aging?
They are a short list of shared cellular changes that researchers use to organize the biology of aging: twelve in the current version, including genomic instability, telomere attrition, epigenetic drift, failing protein quality control, mitochondrial decline, the build-up of senescent cells, and chronic inflammation. The list ties the processes together and is a framework for organizing evidence, not a proven sequence of cause and effect.
Are the epigenetic aging tests worth buying?
As a personal decision tool, not yet. The clocks are real science and predict risk across populations, but different clocks disagree on the same blood sample, a single reading is noisy, and no clock has been shown to be an endpoint that means you will live longer if you lower it. They belong in research, and the "reverse your age" claims attached to them are not established in humans.
What about rapamycin, metformin, NMN and senolytics?
They are still in trials for this purpose. Rapamycin lengthens life in mice but is an immunosuppressant not shown to extend healthy human life; metformin is only now being tested for aging in the TAME trial; senolytics have been through only tiny early studies of cellular markers; NAD precursors such as NMN raise NAD levels without a demonstrated effect on aging. None is established to slow aging in a healthy person, and all carry trade-offs.
If most of it is early, what actually works?
The ordinary habits, and they are not minor. Not smoking, cardiorespiratory fitness, keeping a healthy weight, regular movement and muscle, and a good diet track with roughly a decade of extra life expectancy in large studies, and they act on the same hallmarks the drugs target. They are cheaper, safer and far better evidenced than any clock or supplement.
Explore Related
Other pages this one connects to, by the evidence they share, the outcomes they touch, and the ground they cover.
All 15 sources on this page independently checked and cross-referenced.
Thomas Dehli, Founder & Editor, Sacred Lotus
Sacred Lotus has published Chinese medicine reference material since 2001. Integrative pages are held to the same standard as the herb and formula library: cite the source, grade the claim at its real strength, and say where the research has not looked. This page is educational and it is not medical advice. Last reviewed and updated August 10, 2026.
Evidence strength
How confidently the research supports a claim. Strength describes the evidence, not our endorsement.