How can I measure my biological age?

DNA methylation is currently the best-supported method for estimating biological age. Specialised measurement tools called epigenetic clocks read patterns in how your DNA is 'tagged' without the genetic code itself changing. Those patterns shift with age in a predictable way, allowing an estimate of how old your body looks from a biological standpoint.

Two clocks stand out because of their predictive power. GrimAge, which incorporates smoking history and certain protein levels in the blood among other factors, strongly predicted in studies with thousands of participants who died earlier, developed cardiovascular disease, or went on to develop cancer. A second clock, PhenoAge, is based on clinical measures and outperforms older clocks in predicting mortality, physical functioning, and diseases such as Alzheimer's. People who are epigenetically 'older' than their calendar age also tend to have more chronic inflammatory activity and less well-functioning energy factories in their cells.

Alongside DNA methylation, there are methods that look at gene activity, protein profiles, or metabolic products. Machine learning is used to combine these into new types of 'clocks'. Which combination works best is still very much an active area of research.

Telomere length, the protective caps at the ends of chromosomes, is sometimes mentioned as a measure of biological age. Current reviews, however, clearly rank it below epigenetic methods, with more limited predictive value.

There are still considerable limitations. Epigenetic clocks are sensitive to the types of cells present in a blood sample, which can influence the result. How to interpret the outcomes precisely has not yet been fully resolved. And the fact that a higher biological age is associated with worse health outcomes does not yet mean that the clock can also indicate whether a treatment has genuinely changed something; long-term follow-up studies are needed for that.