Do ageing clocks predict lifespan in animals?

Human lifespan studies can take decades. In mice and short-lived fish, researchers can measure biological age, give a treatment and record survival within a much shorter period. The design must distinguish a clock that predicts an animal’s mortality risk from a clock that changes when a treatment extends lifespan.

A good predictor need not be part of the ageing mechanism. Drugs can alter the biomarker it reads without producing a comparable benefit in the animal.

Mice: known longevity interventions affect the clock

A 2017 study derived a methylation clock from 107 mouse liver samples. It analysed 28 further liver samples comprising longevity-intervention groups and their controls, and found younger predicted ages in dwarf, calorie-restricted or rapamycin-treated mice than in age-matched controls. These interventions are already associated with longer mouse lifespan.

The groups were small, and the investigators collected liver at particular ages. They did not follow those individual mice after sampling to test whether the size of each clock change predicted time of death.

A later longitudinal study combined frailty and blood data to develop phenotypic-age models. Methylation- and metabolite-based predictions were associated with remaining mouse lifespan even after chronological age was taken into account.

Dogs and killifish provide different tests

A Dog Aging Project preprint analysed DNA methylation from 864 companion dogs. Higher age-adjusted epigenetic age was associated with mortality after accounting for factors including breed size. The analysis was observational and has not established how treatment would change risk.

In killifish, some dietary-restriction regimes extend male lifespan without a comparable effect in females. A March 2026 Nature Aging study used RNA-expression clocks and found lower predicted liver age after restriction in males, with no statistically established reduction in females. These were transcriptomic clocks, not methylation clocks.

Testing whether clock changes predict lifespan gains

A stronger test would randomise animals to several treatments, measure clocks before and during treatment, and follow them to death. Investigators could then check whether the size of a clock change predicts the survival benefit across treatments that were not used to train the model.

For now, the animal evidence supports clocks as useful correlates of ageing and, in some cases, predictors of mortality. It does not support converting a year of clock reversal into a year of extra life.