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Biological age, explained

How old is your body, really?

Biological age estimates how far your body has aged, measured from blood, DNA or fitness rather than counted from your birth date. How each method works, where it falls short, and how Genoryx reads it.

9
markers in PhenoAge
3
ways to measure it
±15
years, the bound we apply

Two 45-year-olds

Same birthday. Different bodies.

Your calendar age rises by exactly one year every year. Your body does not keep that schedule. In a group of people followed from birth, by 38 some had aged close to zero biological years per calendar year and others nearly three.7

Biological age is the attempt to measure that difference: to compare your markers with how those markers usually look at each age, and to say where you sit. The chart shows two hypothetical people who start level at 30 and age at different paces.

Calendar age

45

Person A

42.8

Person B

47.3

Illustration: at calendar age 45, hypothetical person A has a biological age of 42.8 and person B 47.3.3040506070803040506070calendar agebiological age
  • Person A · 0.85 years per year
  • Person B · 1.15 years per year
  • Same as calendar age

Illustrative · two hypothetical people, not a prediction for anyone

The methods

Three ways to measure it, compared honestly.

Each reads something different, so each is good for something different. None is a complete answer on its own.

Blood-based clocks1,2,3

from a routine draw

Reads
Standard blood chemistry and a blood count, combined with calendar age.
Examples
PhenoAge uses nine markers plus age. The Klemera–Doubal method weighs whichever age-linked markers are available.
Good for
Cheap, repeatable and built from tests most people already have. In a large US population sample, a higher phenotypic age tracked higher risk of death and disease.
Limits
Across people, the estimate sits six to seven years either side of calendar age. A cold the week before raises CRP and white cells and can push it up.
What it takes
A routine blood draw.

Epigenetic clocks4,5,6

from DNA methylation

Reads
Chemical marks on DNA at hundreds of sites that change predictably with age.
Examples
Horvath (353 sites), GrimAge (trained on time to death) and DunedinPACE, which reports a pace in biological years per calendar year rather than an age.
Good for
GrimAge is among the strongest predictors of lifespan and healthspan of any clock. DunedinPACE gives a pace from a single sample.
Limits
Different clocks give different numbers for the same person, and one reading carries measurement noise. Most were trained on non-Indian cohorts.
What it takes
A specialised laboratory; results take a few weeks and cost more than routine bloods.

Functional measures9

from what your body can do

Reads
Aerobic capacity (VO2 max), grip strength, and muscle and bone measured by DEXA.
Examples
Compared against age- and sex-matched norms rather than converted into a single age.
Good for
They respond to training and show capacity directly. Low cardiorespiratory fitness carried one of the highest mortality risks in a cohort of more than 120,000 adults.
Limits
Not an age in years, and effort, equipment and protocol all affect the result.
What it takes
Clinic equipment and a supervised test.

The nine blood markers in PhenoAge, plus your age.1

Most are on a routine panel already. Together they cover nutrition, kidney function, blood sugar, inflammation and the immune system.

  • 01

    Albumin

    Serum Albumin

    The main protein in your blood, made by your liver.

  • 02

    Creatinine, the kidney filter check

    Serum Creatinine

    A waste product your muscles make all day, which your kidneys clear out.

  • 03

    Fasting sugar

    Fasting Plasma Glucose

    The sugar in your blood after a night with no food.

  • 04

    CRP, the inflammation marker

    C-Reactive Protein

    A protein your liver makes fast when you get an infection or a wound.

  • 05

    Lymphocyte share

    Lymphocytes (%)

    The share of your white cells that remember past infections.

  • 06

    Red cell size

    Mean Corpuscular Volume

    The average size of your red cells.

  • 07

    Red cell size spread

    RDW-CV

    How mixed the sizes of your red cells are.

  • 08

    Alkaline phosphatase

    Alkaline Phosphatase

    An enzyme that comes from your bones and from your bile ducts.

  • 09

    White cells

    Total Leukocyte Count

    The total count of the cells your body fights infection with.

  • +

    Calendar age

    The formula starts from your age and adjusts it by what the nine markers say.

How Genoryx reads it

Seven rules, written into the code.

These are the rules our report software follows when it estimates biological age from your results, before a physician ever sees the number.

  1. Use a validated clock when there is one

    If an epigenetic report is part of your results, its clock outputs are used directly, weighted by how well each has held up in published work, with GrimAge highest. DunedinPACE is reported separately as a pace and never folded into the age.

  2. Run the published formula when the panel allows it

    When all nine PhenoAge markers are on a blood panel, the Levine 2018 method applies, cross-checked with the Klemera–Doubal method on the wider panel.

  3. Refuse to extrapolate

    Most lab panels are partial. When key markers are missing, the formulas are not stretched to fit; the reading falls back to how far the available markers sit from normal together, and confidence is marked lower.

  4. Read Indian deficiencies as nutrients, not ageing

    Low vitamin D, low B12, B12-driven homocysteine and low iron stores in women before menopause are common in India. They are flagged as things to correct and left out of the age, so a nutrient gap does not read as faster ageing.

  5. Keep the answer inside what clocks have ever shown

    The result stays within 15 years of calendar age, roughly the outer edge of what published clocks report in real people. A larger gap is far more likely to be a unit error than biology.

  6. Print a range, with its confidence

    A second, fixed formula runs on the same numbers as a cross-check. The report shows a range that spans both, widened when data is thin. If the two disagree by more than eight years, confidence is marked low and the case is logged for review.

  7. Put it in front of a physician

    Fitness, body composition and history are not squeezed into the number. A physician reads the range alongside them, which is where it becomes useful.

See every rule applied to one fictional member in the sample report walkthrough.

What moves it

The markers move. The clock, less certainly.

Established

Regular aerobic and strength training, enough sleep, not smoking, and keeping blood pressure, cholesterol and blood sugar in range.

These move the markers that blood clocks are built from, and they are linked to longer, healthier lives in their own right.

Early

Changing the clock number itself.

Trials are few, small and modest. In a two-year randomised trial, calorie restriction slowed DunedinPACE slightly and did not change PhenoAge or GrimAge.8

This is general education, not advice for you. What suits you depends on your results and history, and a physician decides it with you.

What it cannot tell you

A test gives context, not a diagnosis.

  • One reading is noisy

    An infection, a hard training week or a poor night before the draw can move inflammatory and blood-count markers. The trend across repeat tests says more than any single number.

  • Clocks disagree

    Two clocks can differ by several years for the same person because they were trained to predict different things. When they do, we say so rather than average the difference away.

  • It is context, not a diagnosis

    An older biological age does not name a disease or say when one will appear. A younger one is not a guarantee. A test gives context; the diagnosis, if there is one, comes from a physician.

  • Reference groups are mostly not Indian

    PhenoAge was built in US population surveys, and most epigenetic clocks in American and European cohorts. Indian norms for HDL, hs-CRP, vitamin D and body fat differ, which is why we adjust how some markers are read.

Free, about three minutes

Get a free biological-age estimate

Answer a short questionnaire with Oraia, the Genoryx assistant, or upload a blood report you already have.

Start with Oraia

At our Hyderabad clinics

Measure it properly

An epigenetic test inside the 400+ parameter entry assessment, read with you by a physician.

The biological age test

Questions people ask.

What is biological age?

Biological age is an estimate of how far your body has aged, calculated from measurements such as blood markers, DNA methylation or fitness, rather than counted from your birth date. Two people born in the same year can have different biological ages.

How is biological age different from chronological age?

Chronological age is the number of years since you were born. Biological age is a measurement that compares your markers with how those markers typically look at each age. In a cohort followed from birth, the pace of ageing in 38-year-olds ranged from close to zero to nearly three biological years per calendar year.

Which biological age test is the most accurate?

There is no single best test. Among epigenetic clocks, GrimAge is one of the strongest predictors of lifespan and healthspan. Blood-based PhenoAge is cheaper and uses routine tests. Each carries error of several years for one person, so we read more than one source where possible and follow the trend.

Can biological age be reversed?

The markers that clocks are built from respond to training, sleep and metabolic care. Evidence that interventions move the clock number itself is early and modest: in a two-year trial, calorie restriction slowed one clock slightly and left two others unchanged. No outcome should be promised in advance.

Does a biological age test diagnose disease?

No. A biological age test gives context, not a diagnosis. It cannot name a condition or predict when one will appear. A physician reads it alongside your history, examination and other results.

Is the free online estimate the same as a test?

No. The free Oraia estimate uses a short questionnaire, or a blood report you already have. It is a useful starting point. A measured biological age at Genoryx comes from a full panel read by a physician.

How often should biological age be measured?

Often enough to see a trend, under similar conditions each time. Genoryx members are re-measured every 90 days, so each reading can be compared with the one before it.

References

  1. 1.Levine ME, et al. An epigenetic biomarker of aging for lifespan and healthspan. Aging, 2018;10(4):573–591.
  2. 2.Liu Z, et al. A new aging measure captures morbidity and mortality risk across diverse subpopulations from NHANES IV. PLOS Medicine, 2018.
  3. 3.Kwon D, Belsky DW. A toolkit for quantification of biological age from blood chemistry and organ function test data: BioAge. GeroScience, 2021.
  4. 4.Horvath S. DNA methylation age of human tissues and cell types. Genome Biology, 2013.
  5. 5.Lu AT, et al. DNA methylation GrimAge strongly predicts lifespan and healthspan. Aging, 2019.
  6. 6.Belsky DW, et al. DunedinPACE, a DNA methylation biomarker of the pace of aging. eLife, 2022.
  7. 7.Belsky DW, et al. Quantification of biological aging in young adults. PNAS, 2015.
  8. 8.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.
  9. 9.Mandsager K, et al. Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing. JAMA Network Open, 2018.

Educational content. Nothing on this page is a diagnosis or a treatment recommendation. Related reading: what is biological age, epigenetic clocks explained, the science.

Your biological age is a number you can measure.

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