A biological age test measures how your body is ageing internally — regardless of the number on your birth certificate. Two 40-year-old men can have biological ages a decade apart based on their metabolic health, inflammatory markers, cardiovascular fitness, and epigenetic profiles. The man with the lower biological age is, by every measurable standard, healthier and more likely to live longer with fewer chronic diseases.
Bryan Johnson — the tech entrepreneur who spends $2M annually on a longevity protocol — has popularised biological age testing by publicly tracking his own metrics and reporting a biological age 18 years younger than his chronological age. His approach is maximalist and unreplicable for most men. But the underlying principle is sound: you can't optimise what you don't measure, and chronological age tells you almost nothing about your actual health trajectory.
For men over 35, a biological age test provides the data that transforms vague health anxiety into specific, actionable targets. This article covers which tests to take, what the numbers mean, and — critically — which lifestyle levers move each biomarker.
What is a biological age test? A biological age test estimates your body's internal ageing rate using biomarkers that correlate with health outcomes more strongly than chronological age. The most validated approaches are epigenetic clocks (measuring DNA methylation patterns — Horvath clock, GrimAge), blood biomarker panels (inflammation, metabolic function, organ health), and functional tests (VO2 max, grip strength). Epigenetic age tests are the most scientifically rigorous but cost £250–400. Blood biomarker panels (£80–180) are more accessible and provide immediately actionable data. Both are available in the UK through private testing services.
Check Biological Age: What the Science Measures
Epigenetic clocks: the gold standard
Epigenetic clocks measure patterns of DNA methylation — chemical modifications to DNA that change with age. The most validated clocks include:
Horvath Clock (2013): The original epigenetic clock, trained on 8,000 samples. Estimates biological age based on methylation at 353 CpG sites. Accurate to within 3.6 years on average.
GrimAge (2019): Second-generation clock that incorporates plasma protein markers alongside methylation data. Predicts mortality and disease onset more accurately than the Horvath clock. A 2023 review identified GrimAge as the most useful epigenetic clock for predicting health outcomes (Cell, Moqri et al., 2023).
DunedinPACE (2022): Measures the pace of ageing rather than biological age — how fast you're ageing right now, not how old your body appears. This is particularly useful for tracking interventions because it responds to lifestyle changes faster than static age estimates.
Availability in UK: TruDiagnostic TruAge (£300–400), GlycanAge (£250–350), and Muhdo (£150–250) offer consumer epigenetic testing with UK delivery. Results take 4–6 weeks.
Blood biomarker panels: the practical approach
For most men, a comprehensive blood panel provides more immediately actionable data than an epigenetic clock — and at a fraction of the cost.
Key longevity biomarkers:
| Biomarker | What It Measures | Target Range | Why It Matters |
|---|---|---|---|
| hsCRP | Systemic inflammation | <1.0 mg/L | Chronic inflammation accelerates every ageing pathway |
| HbA1c | Blood sugar control (90-day avg) | <5.6% (ideally <5.4%) | Metabolic dysfunction is the primary driver of age-related disease |
| Fasting insulin | Insulin sensitivity | <5 µIU/mL (optimal) | Insulin resistance precedes diabetes by 10–15 years |
| ApoB | Atherogenic particles | <90 mg/dL (ideally <80) | Single best predictor of cardiovascular risk |
| ALT | Liver function | <25 U/L (optimal) | Elevated ALT signals metabolic stress and fatty liver |
| Testosterone (total + free) | Hormonal health | >15 nmol/L total | Declines ~1% annually from 30; trackable and modifiable |
| Cortisol | Stress response | See diurnal pattern | Elevated cortisol accelerates every biomarker on this list |
| Vitamin D (25-OH) | Immune and hormonal function | 75–125 nmol/L | 50–70% UK men deficient in winter |
Where to test in the UK: Medichecks Advanced Health Check (£149), Forth Vitality (£129), or Thriva Baseline (£79). Request your GP test these via NHS if you present with relevant symptoms.
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Biological Ageing Test: Functional Markers
Blood tests measure internal biochemistry. Functional tests measure what your body can actually do — and several are among the strongest predictors of all-cause mortality.
VO2 max: the single best predictor of longevity
VO2 max — maximal oxygen uptake during exercise — is the strongest independent predictor of all-cause mortality in the medical literature. A 2018 JAMA Network Open study of 122,007 patients found that cardiorespiratory fitness was inversely associated with all-cause mortality with no upper limit of benefit. Men in the lowest fitness quartile had 5x the mortality risk of men in the highest quartile.
How to test: Gold standard is a laboratory graded exercise test (£100–200 at sports medicine clinics). Approximations: many fitness watches estimate VO2 max from heart rate data. The Cooper 12-minute run test provides a reasonable estimate (distance in metres / 35 − 11.3 = estimated VO2 max).
Target: Maintain VO2 max above the 75th percentile for your age group. For a 40-year-old man, this means approximately 42–46 mL/kg/min. Aerobic exercise directly improves VO2 max — and the neuroplasticity and brain health benefits come as a bonus.
Grip strength
Grip strength correlates with all-cause mortality independently of muscle mass, body size, and exercise habits. A 2015 Lancet study of 140,000 adults found that each 5kg decrease in grip strength was associated with a 17% increase in cardiovascular mortality and a 16% increase in all-cause mortality.
How to test: Hand dynamometer (available for £20–30 on Amazon). Test both hands, take the average of three attempts. Normative values for men aged 35–44: 47–55 kg.
How to improve: Resistance training — particularly deadlifts, rows, and farmer's carries — directly increases grip strength. It's not a separate exercise; it's a byproduct of training properly.
Resting heart rate
Lower resting heart rate is associated with lower cardiovascular and all-cause mortality. A meta-analysis found that each 10 bpm increase in resting heart rate was associated with a 9% increase in cardiovascular mortality.
Target: <65 bpm. Elite endurance athletes typically rest at 40–50 bpm. Most untrained men sit at 70–85 bpm. Aerobic exercise reliably reduces resting heart rate within 4–8 weeks.
Epigenetic Clock Test: What Moves the Numbers
The most important question isn't what your biological age is — it's what you can do about it. Research on epigenetic clock acceleration shows consistent effects from specific interventions:
Interventions that reduce biological age:
| Intervention | Evidence | Magnitude |
|---|---|---|
| Aerobic exercise (150+ min/week) | Multiple RCTs | 1.5–3 years biological age reduction |
| Mediterranean-style diet | PREDIMED trial analysis | 1.5–2 years |
| Sleep quality (7–9 hours) | Observational + RCTs | 1–2 years |
| Stress reduction (meditation, cortisol management) | Emerging RCTs | 0.5–2 years |
| Smoking cessation | Large cohort studies | 3–5 years within 5 years |
| Moderate alcohol or abstinence | Mendelian randomisation | 0.5–1.5 years |
Interventions with preliminary evidence:
| Intervention | Status |
|---|---|
| Creatine supplementation | Cognitive age markers improve; epigenetic data pending |
| Caloric restriction / fasting | CALERIE trial showed biological age deceleration |
| Rapamycin (prescription) | Multiple clinical trials underway |
| NAD+ precursors (NMN/NR) | Inconsistent results; more research needed |
The pattern is clear: the lifestyle interventions that support biological age are the same ones that support every other health outcome — exercise, sleep, stress management, nutrition. There is no shortcut that bypasses the fundamentals.
My Biological Age: A Practical Testing Protocol
Year 1: Establish your baseline
Month 1: Comprehensive blood panel (Medichecks or Forth, £80–180). Test all biomarkers listed above. Note which are outside optimal range.
Month 1: Functional tests at home. Resting heart rate (morning, before getting up). Grip strength (dynamometer). VO2 max estimate (Cooper test or fitness watch).
Month 1 (optional): Epigenetic age test (TruDiagnostic or GlycanAge, £250–400) if budget allows.
Months 2–6: Address the lowest-hanging fruit from your blood panel. If vitamin D is low, supplement. If HbA1c is elevated, address carbohydrate quality and exercise. If testosterone is low, investigate sleep, stress, and body composition first.
Month 6: Retest blood panel. Compare. The biomarkers that moved tell you which interventions are working. The ones that didn't tell you where to focus next.
Ongoing: Annual cycle
Comprehensive blood panel annually (minimum). Functional tests quarterly (grip strength, resting heart rate, body composition). Epigenetic test every 1–2 years if tracking long-term biological age trends.
Biological Age Test Free: What You Can Measure Without Spending
Several biological age indicators cost nothing:
Resting heart rate: Check with your finger on your wrist for 60 seconds each morning before getting up. Track weekly average.
Waist-to-height ratio: Measure waist at navel. Divide by height. Below 0.5 is associated with lower metabolic risk. Above 0.6 indicates elevated risk.
Get-up-from-floor test: Sit on the floor cross-legged, then stand up without using your hands. Ability to do this without support is independently associated with lower mortality risk in adults.
Recovery heart rate: After moderate exercise, measure how quickly your heart rate drops. A drop of >12 bpm in the first minute post-exercise indicates good cardiovascular autonomic function.
These aren't substitutes for blood testing — but they're free, repeatable, and provide genuine signal about your biological age trajectory.
Frequently Asked Questions
What is a biological age test?
A biological age test estimates how your body is ageing internally using biomarkers that predict health outcomes more accurately than chronological age. Methods include epigenetic clocks (DNA methylation patterns, £250–400), blood biomarker panels (inflammation, metabolic, hormonal markers, £80–180), and functional tests (VO2 max, grip strength). Two men of the same chronological age can have biological ages a decade apart.
How can I check my biological age?
Start with a comprehensive blood panel through Medichecks, Forth, or your GP — testing hsCRP, HbA1c, fasting insulin, ApoB, ALT, testosterone, vitamin D, and cortisol. Add functional tests at home: resting heart rate, grip strength, waist-to-height ratio. For the most scientifically rigorous assessment, an epigenetic clock test (TruDiagnostic, GlycanAge) provides a DNA methylation-based biological age estimate.
Can you reduce your biological age?
Yes. Aerobic exercise (150+ min/week), quality sleep (7–9 hours), Mediterranean-style nutrition, stress management, and smoking cessation all reduce biological age in studies using epigenetic clocks. The CALERIE trial showed that moderate caloric restriction decelerated biological ageing. Effects of 1.5–3 years of biological age reduction are consistently observed from sustained lifestyle interventions.
How accurate are biological age tests?
Epigenetic clocks (GrimAge, DunedinPACE) are the most accurate, predicting mortality and disease onset better than chronological age. The Horvath clock has a mean error of approximately 3.6 years. Blood biomarker panels provide actionable data but don't calculate a single "biological age" number — they show where individual systems are performing well or poorly. Functional markers (VO2 max, grip strength) are among the strongest all-cause mortality predictors available.
What is the most important longevity biomarker?
VO2 max. A 2018 study of 122,007 patients found cardiorespiratory fitness was the strongest independent predictor of all-cause mortality — more predictive than smoking, diabetes, or hypertension. Men in the lowest fitness quartile had 5x the mortality risk of those in the highest. VO2 max is also the most modifiable longevity biomarker — it responds directly and measurably to aerobic exercise.
Key Takeaways
- Biological age and chronological age can differ by a decade or more — testing reveals where you actually stand
- VO2 max is the single strongest predictor of all-cause mortality — maintain above the 75th percentile for your age
- A comprehensive blood panel (£80–180) is the most actionable first test — it tells you exactly which systems need attention
- The interventions that reduce biological age are the fundamentals — exercise, sleep, stress management, nutrition
- Test annually, act on what you find, retest — biological age is modifiable, not fixed
References
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Moqri M, et al. Biomarkers of aging for the identification and evaluation of longevity interventions. Cell. 2023.
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Erickson KI, et al. Exercise training increases size of hippocampus and improves memory. PNAS. 2011.
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Mandsager K, et al. Association of cardiorespiratory fitness with long-term mortality among adults. JAMA Network Open. 2018.
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Leong DP, et al. Prognostic value of grip strength. The Lancet. 2015.
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Horvath S. DNA methylation age of human tissues and cell types. Genome Biology. 2013.
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Lu AT, et al. DNA methylation GrimAge version 2. Aging. 2022.
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Belsky DW, et al. DunedinPACE: a DNA methylation biomarker of the pace of aging. eLife. 2022.
This is educational content, not medical advice. Consult your doctor before making changes to your health, fitness, or nutrition regimen.