By Dr Andrew Fang is a Medical Director at Doctor Anywhere
Chronological age is simple – it ticks up by one with every birthday, and everyone already knows their number. Biological age is not. It reflects how fast or slow a person’s body is actually ageing at the cellular level, and increasingly, science has found ways to measure that gap directly.
To understand why two people of the same chronological age can be ageing so differently, it helps to look at epigenetics – the layer of chemical instructions sitting on top of your DNA that tells genes when to switch on or off. A queen bee and a worker bee, for instance, share virtually identical genomes, yet one grows larger, lives for years, and reproduces, while the other lives for weeks and never does – the difference comes down almost entirely to what each was fed as a larva, which flips different genes on and off. Identical human twins tell a similar story: they start life with the same DNA, but decades later, one twin can look and age noticeably differently from the other, depending on things like smoking, diet, stress, and sun exposure. The DNA sequence never changed. What changed was which parts of it got used, and how consistently, over time – and that layer is exactly what biological age tests are picking up on.
The most researched approach uses DNA methylation – chemical modifications to DNA that change in predictable patterns as cells age – to estimate a person’s biological age from a simple sample. These are often called epigenetic clocks, and the field has moved quickly: earlier versions focused on predicting chronological age, while newer generations are designed instead to measure the pace at which someone is ageing, not just produce a static number. A 2024 study in the journal Alzheimer’s & Dementia, using Framingham Heart Study data, found that a faster pace of biological ageing was associated with worse cognitive performance and steeper cognitive decline over time – independent of education level.
What makes this indicator distinctive is that it captures cumulative impact – the combined effect of genetics, lifestyle, environment, and stress on the body over years – in a single measurement, rather than looking at one organ system at a time the way most other tests do. More recent research has linked faster biological ageing to smoking, higher BMI, elevated blood glucose, and poor blood pressure control, while physical activity and healthier diet patterns are associated with a slower pace.
It’s worth being clear-eyed about the science here too: researchers are still refining exactly how these measurements should be interpreted clinically, and this remains an active, evolving area of research rather than a settled one. What’s well-established is that scientists have found those whose biological age – as measured by their DNA markers – runs faster than their actual age face meaningfully higher health risk over time.
“Scientists have found that those whose biological age – as measured by their DNA markers – runs faster than their actual age face meaningfully higher health risk over time.”
– Dr Andrew
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