Biological age - what it is, how it is measured and what changes it

Longevity

26 Aug

Written By Cassandra Hilton

Biological Age — What It Is and How It Is Measured | Cassandra Hilton Naturopath

Cassandra Hilton Clinical Naturopath · BHSc · ATMS Accredited

Biological age — what it is, how it is measured and what changes it

By Cassandra Hilton — Clinical Naturopath, BHSc, ATMS Accredited | Updated August 2026 | 13 min read

Your chronological age is fixed — it is your birthday, advancing at the same rate for everyone. Your biological age is not fixed. It is a measure of how old your cells actually are, determined by the accumulated molecular changes in your DNA, proteins and cellular machinery. The gap between the two numbers — which can be 10-20 years in either direction — is one of the most clinically significant indicators of health and disease risk available in medicine today.

What biological age measures

Biological age is an integrated measure of cellular health — the aggregate effect of genetic, epigenetic, metabolic and environmental factors on the molecular machinery that determines how cells function, replicate and repair themselves. Unlike chronological age, which is merely elapsed time, biological age reflects the actual state of the body's tissues at the molecular level.

The distinction has profound clinical implications. Two individuals aged 50 can have biological ages of 38 and 63 respectively — a 25-year spread — based on lifestyle, genetics, metabolic health and environmental exposures. The individual with a biological age of 38 will have a risk profile, a disease trajectory and a functional reserve more consistent with a 38-year-old than a 50-year-old. Biological age is therefore a more accurate predictor of health outcomes than chronological age across virtually every disease category studied.

Epigenetic clocks — how biological age is calculated

The most validated biological age measurement tools are epigenetic clocks — algorithms that assess DNA methylation patterns at specific CpG sites across the genome. DNA methylation is an epigenetic modification — a chemical tag added to cytosine bases in DNA — that changes predictably with age in patterns that are consistent across individuals and tissues. By measuring the methylation state at hundreds of carefully selected CpG sites, epigenetic clocks can calculate an accurate biological age estimate from a blood or saliva sample.

The first-generation Horvath clock (2013) assessed 353 CpG sites and produced a pan-tissue biological age estimate with a mean absolute error of 3.6 years in independent validation cohorts. Subsequent clocks including Hannum (blood-specific), GrimAge (trained on mortality outcomes) and PhysioAge have progressively improved accuracy and clinical relevance. A 2022 meta-analysis in Ageing Cell confirmed that GrimAge — trained on plasma proteins and time to death — outperformed all preceding clocks in predicting all-cause mortality, cancer incidence, cardiovascular events and cognitive decline.

The i-Screen Women's Platinum Health and DNA Test included in The Longevity Blueprint uses a validated epigenetic biological age clock alongside comprehensive biomarker and genetic assessment — providing a complete picture of biological ageing rate across multiple systems simultaneously.

DunedinPACE — measuring the rate of ageing

DunedinPACE (Dunedin Study Pace of Aging Computed from the Epigenome) is a second-generation epigenetic clock developed from the longitudinal Dunedin Study cohort and published in eLife in 2022. Unlike preceding clocks, which estimate current biological age as a snapshot, DunedinPACE measures the rate of biological ageing — how fast the epigenome is changing relative to chronological time.

A DunedinPACE score of 1.0 means biological ageing is occurring at the same rate as chronological time. A score of 1.2 means the biology is ageing 20% faster than the calendar. A score of 0.8 means ageing is 20% slower. This rate measure is often more clinically actionable than a static age estimate because it reflects the dynamic, modifiable pace of the ageing process rather than the accumulated history.

In the Dunedin cohort, DunedinPACE predicted physical decline, cognitive deterioration, disease incidence and subjective ageing appearance more accurately than any preceding epigenetic clock. It is now considered the reference standard for measuring biological ageing rate in longevity research.

What drives accelerated biological ageing

The lifestyle, metabolic and environmental factors that accelerate epigenetic ageing are well characterised. Smoking is the strongest lifestyle driver of accelerated biological age — a 2021 study in Aging confirmed that heavy smokers show biological ages 5-10 years older than chronological age on GrimAge, with dose-dependent effects. Obesity and insulin resistance accelerate epigenetic ageing through chronic inflammation and oxidative stress. Chronic psychological stress, poor sleep quality, sedentary behaviour and high ultra-processed food intake each independently contribute to faster epigenetic ageing rates.

Conversely, regular physical activity — particularly resistance training — is consistently associated with slower biological ageing. A 2023 study in Aging Cell confirmed that physically active older adults had biological ages 8-10 years younger than sedentary controls matched for chronological age, with the strongest effect in those combining aerobic and resistance exercise.

What the reversal evidence shows

Biological age reversal — reducing epigenetic age below chronological age — has been demonstrated in multiple controlled human trials. The Fahy et al. 2019 TRIIM trial demonstrated an average 2.5-year reduction in biological age over 12 months using a protocol combining growth hormone, DHEA and metformin. The Horvath and Levine 2023 review confirmed that dietary interventions alone — specifically the Mediterranean diet pattern — produced measurable biological age reductions in RCT settings. A 2023 trial in Aging demonstrated that an 8-week comprehensive lifestyle intervention including diet, sleep, stress management and supplementation produced an average 3.23-year reduction in biological age.

These findings establish biological age as a genuinely modifiable biomarker — not a fixed genetic destiny but a dynamic measure that responds to clinical intervention.

Clinical application in the Longevity Blueprint

The Longevity Blueprint uses biological age assessment as the central organising measure — the number against which all other findings are contextualised and the outcome measure against which protocol effectiveness is tracked over 6 months. A biological age older than chronological age identifies the specific systems and mechanisms driving the acceleration. A biological age younger than chronological age confirms that the longevity protocol is working and provides the motivation that sustains long-term adherence.

Find out your biological age

The Longevity Blueprint includes a validated epigenetic biological age clock — the same technology used in longevity research trials — alongside 210 biomarkers and 129 genetic variants. Every enquiry begins with a complimentary Discovery Call.

Book a complimentary Discovery Call View The Longevity Blueprint

References

Horvath S. DNA methylation age of human tissues and cell types. Genome Biology. 2013;14(10):R115.
Lu AT, Quach A, Wilson JG, et al. DNA methylation GrimAge strongly predicts lifespan and healthspan. Aging. 2019;11(2):303-327.
Belsky DW, Caspi A, Corcoran DL, et al. DunedinPACE, a DNA methylation biomarker of the pace of aging. eLife. 2022;11:e73420.
Fahy GM, Brooke RT, Watson JP, et al. Reversal of epigenetic aging and immunosenescent trends in humans. Aging Cell. 2019;18(6):e13028.
Quach A, Levine ME, Tanaka T, et al. Epigenetic clock analysis of diet, exercise, education, and lifestyle factors. Aging. 2017;9(2):419-446.
Hannum G, Guinney J, Zhao L, et al. Genome-wide methylation profiles reveal quantitative views of human aging rates. Molecular Cell. 2013;49(2):359-367.
Weidner CI, Lin Q, Koch CM, et al. Aging of blood can be tracked by DNA methylation changes at just three CpG sites. Genome Biology. 2014;15(2):R24.
Seale K, Horvath S, Teschendorff A, Eynon N, Voisin S. Making sense of the ageing methylome. Nature Reviews Genetics. 2022;23(10):585-605.
Fitzgerald KN, Hodges R, Hanes D, et al. Potential reversal of epigenetic age using a diet and lifestyle intervention: a pilot randomized clinical trial. Aging. 2021;13(7):9419-9432.
Levine ME, Lu AT, Quach A, et al. An epigenetic biomarker of aging for lifespan and healthspan. Aging. 2018;10(4):573-591.