Why mice age fast and humans age slowly

Ageing is linked to the accumulation of damage in cells. But why does this happen so much faster in some species than others? The researchers used a so-called ‘saturating removal model’ (a mathematical description of how damage builds up and is cleared) and fitted it to survival data from dozens of species, from yeast to dogs to humans. The study was published in Nature Aging.

Two distinct ways of growing old

The model identifies two clearly different ageing regimes. In short-lived animals such as mice, fruit flies and nematodes, damage is produced faster than the body can remove it. Damage accumulates like an avalanche. In long-lived animals, including humans, dogs and guinea pigs, the body keeps damage and repair in balance for longer. Ageing only sets in as that equilibrium gradually shifts.

The parameter that best predicts lifespan is the rate at which damage is produced. This varies between species by a factor of ten million. Other parameters, such as the threshold at which damage becomes lethal, appear less variable. This suggests that the key to a long life lies not so much in better damage removal, but in a lower rate of cellular damage production.

What this means for longevity research

The distinction between mice and humans is relevant for longevity research. Many interventions that extend mouse lifespan do not work the same way in humans. This model offers a possible explanation: mice and humans operate in different biological regimes. An intervention that lowers damage production may work differently in an avalanche regime than in an equilibrium regime.

The authors emphasise that the model is a simplification and requires experimental validation. It is a theoretical framework, not a clinical recommendation. Still, it offers a new way to think about why anti-ageing strategies often fail to translate from animals to humans.

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