How reliable are epigenetic clocks for measuring your biological age?

Epigenetic clocks measure your biological age through small chemical tags on your DNA. These tags change at predictable locations as you get older. The accuracy is high: a clock tested across 185 mammal species and 59 tissue types achieves a correlation of more than 0.96 between the measured clock age and the actual age^1,2. That is impressive. In some cell types, such as skin cells from connective tissue, the measurement does work less well.

Certain clocks also predict your future. GrimAge predicts mortality and life expectancy better than your date of birth alone^3,2. But be aware: these are associations, not causes. The fact that GrimAge predicts risk does not mean the clock is measuring ageing itself. The causal mechanism is not yet known.

Whether you can turn back the clock reading is an open question. The TRIIM pilot study tested a combination of growth hormone, DHEA and metformin in nine participants. After one year, the measured clock age was on average 1.5 years lower than at the start. The difference on GrimAge persisted for six months after stopping³. Striking, but the study had no control group, was very small, and the authors had financial interests. No conclusions can therefore be drawn from it yet.

DNA methylation is not the only measurement method. A clock based on which genes are active (BiT age) approaches the theoretical accuracy limit and works even in the roundworm C. elegans, which has no DNA methylation at all⁴. The fact that multiple biological processes produce the same result shows that no single clock tells the full story.

The fact that the same DNA sites change with age in nearly all mammals suggests that ageing is deeply embedded in evolution¹. Epigenetic clocks are therefore valuable research tools. But 'turning back the clock' is not a simple intervention: you are touching processes that have been broadly preserved throughout evolution.