What exercise does to your biological age

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When you hear about billionaire biohackers claiming they are years younger than their chronological age, they are sometimes referring to their epigenetic clocks. These are measures of chemical reactions around our genes called DNA methylation, which can turn genes off or change their level of activity. The most reliable clocks have been calibrated against large populations of people whose health and wellbeing are tracked in detail over time.

The result is a tool that can measure your DNA methylation and indicate, on average, how typical that pattern is for a person of a certain age. You might be 50 but your DNA methylation might resemble that of a 48-year-old or a 53-year-old. That gap between chronological and biological age turns out to matter quite a lot for health outcomes.

The more exercise people did, the younger their biological age.

These clocks have made it possible to study whether specific interventions are associated with being biologically younger or older, in a way that goes beyond the usual self-reported health measures. A recent meta-analysis published in The Lancet brought together 44 studies of exercise involving over 145,000 people to ask exactly that question.

What they found was that the more exercise people did, the younger their biological age. The association held across different types of exercise, different age groups, and different populations. People who exercised regularly showed DNA methylation patterns that were, on average, several years younger than their non-exercising counterparts of the same chronological age.

The important caveat is that the study could not prove cause and effect, and many of the individual associations across the 44 studies did not reach statistical significance. People who choose to exercise may be biologically younger to begin with, for reasons unrelated to the exercise itself. Genetics, socioeconomic factors, diet, sleep, and a range of other variables all influence both exercise behaviour and biological ageing. Further research, ideally using randomised designs, is needed to establish how much of the effect is directly caused by exercise and how much is explained by the kinds of people who exercise.

That said, the consistency of the finding across a very large, combined sample is not easily dismissed. Exercise is already associated with reduced risks of cardiovascular disease, type 2 diabetes, depression, and a range of cancers. The possibility that it is also slowing biological ageing at a cellular level adds another dimension to a conversation that GPs are already well placed to have.