Your biological age is an estimate of how your body is functioning, expressed in years. It usually comes from a formula that compares your blood values against those of your peers. A score of 34 when you are 42 does not mean your organs are 34 years old. It means a handful of markers look better than average.
I have mixed feelings about it. The underlying science is decent, but the way the result gets sold often is not. A score is not a diagnosis, and it certainly is not an age.
What follows is the explanation I wish I had read before ordering one.
What is biological age exactly?
Biological age is a calculated estimate of your functional state, based on measurable markers such as inflammation, blood sugar regulation, kidney function and blood lipids. Your calendar age is fixed. Your biological age is a snapshot that can shift with your lifestyle, your training load and even a recent infection.
The idea comes from research into ageing at the cellular level. Researchers looked for markers that predict how someone fares better than a birth year alone. That worked, but at group level.
That distinction matters. A model that predicts well across a thousand people can still be well off for you personally.
How do you find out your biological age?
There are roughly three routes: a blood model that converts routine markers into a score, an epigenetic clock that measures DNA methylation, and a fitness estimate based on performance. They do not measure the same thing and they are not equally reliable. The blood route is the best supported and the cheapest, while the epigenetic route sounds the most exciting.
The best known blood based method is PhenoAge, developed by Levine and colleagues, which combines nine routine markers with your age (PMID 29676998). Horvath's epigenetic clock measures something quite different, namely methylation patterns on your DNA (PMID 24138928).
| Method | What it measures | Strength | Weakness |
|---|---|---|---|
| Blood model (PhenoAge style) | Albumin, creatinine, glucose, hs-CRP, lymphocytes, MCV, RDW, alkaline phosphatase, white cells | Cheap, repeatable, every marker can be acted on | Sensitive to a cold or a heavy training week |
| Epigenetic clock | DNA methylation at hundreds of sites | Predicts strongly at group level | Expensive, and test to test noise can exceed the effect you want to see |
| Fitness estimate | VO2max, grip strength, recovery rate | Measures function, not chemistry | Says little about inflammation or blood sugar |
See the pattern? Each method measures a different part of the elephant.
Which blood values weigh the most?
In almost every blood model, inflammation and blood sugar regulation carry the most weight. A raised hs-CRP pushes your score up, as does a climbing HbA1c. Albumin and the red cell picture count too, but they move more slowly. That makes inflammation and glucose the two dials worth turning first.
This is no accident. Chronic low grade inflammation runs like a thread through almost every model of ageing (PMID 30065258).
To understand why that one marker weighs so heavily, read what hs-CRP says about ageing. If blood sugar is your weak link, the full story sits in measuring metabolic health.
Why do athletes often score strangely on these tests?
Because the formulas are built on the average population, and you are not that. Training changes precisely the markers the model uses, and not always in the direction the model expects. A well trained man can end up with a worse score than his untrained neighbour, while being fitter.
Four distortions show up most often.
- Creatinine. A lot of muscle mass means structurally higher creatinine. The model reads that as poorer kidney function.
- Hs-CRP after a hard session. A tough lifting session or a long run can lift your hs-CRP for days.
- Haematocrit. Endurance training at altitude, or simply being well trained, shifts your red cell picture.
- Alkaline phosphatase. Bone turnover after repeated impact can nudge this value up.
Picture two men of 42. One trains four times a week and has a creatinine of 105 micromol per litre and an hs-CRP of 2.8 mg/l, two days after a heavy leg day. The other does not train and sits at 78 micromol per litre and 0.9 mg/l. The model hands the athlete the older score. In reality this says more about muscle mass and training timing than about ageing.
This is why I never read a biological age score on its own. The underlying list of markers is genuinely useful. The number above it is marketing.
Can you lower your biological age?
The markers the score is built from can certainly move. Inflammation, blood sugar and lipids respond to sleep, food, alcohol and training load, sometimes within months. Whether that means you are "ageing more slowly" is a different question, because the evidence there is far more cautious than the advertising suggests.
RIVM, the Dutch national institute for public health, tracks how lifestyle factors relate to health in later life, and those figures are more sober than most providers' promises.
My advice: steer by the individual markers, not by the number.
What do you do with the result?
Test fasted, and avoid testing within three days of a hard session or an infection. Then look at the underlying markers rather than the composite score. Always compare a new measurement against your own previous one, because the trend inside your body tells you more than a comparison with an average person.
To see those markers in context, a broad panel such as the 360 Health blood test gives you inflammation, blood sugar, kidney function and lipids in one go. The wider picture sits in the guide on healthy ageing as an athlete, and the muscle side of the story in sarcopenia after 40.
If you order a biological age test, do it to see the markers. Not to see the number.
References
- Levine ME et al. An epigenetic biomarker of aging for lifespan and healthspan. Aging (Albany NY), 2018. PMID 29676998
- Horvath S. DNA methylation age of human tissues and cell types. Genome Biology, 2013. PMID 24138928
- Ferrucci L, Fabbri E. Inflammageing: chronic inflammation in ageing, cardiovascular disease, and frailty. Nature Reviews Cardiology, 2018. PMID 30065258
- RIVM, Public Health Foresight Study, lifestyle and health.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
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