University of Otago study: Sterilisation boosts lifespan across 117 species

Preventing reproduction can extend lifespan in mammals across a wide range of species, a new study has found.

A major international study led by the University of Otago has found that blocking reproduction increases lifespan in both males and females across a wide range of species.

The team examined historical data from mammals kept in zoos and aquariums worldwide, uncovering that both ongoing hormonal contraception and permanent surgical sterilisation are linked to living longer.

Lead author Associate Professor Mike Garratt, of Otago’s School of Biomedical Sciences, said that while males and females benefit to a similar extent, the underlying reasons differ.

“In males, only castration extends lifespan – not vasectomy – which indicates that the effect comes from removing sex hormones. These hormones may interact with pathways that regulate the biology of ageing, particularly during early-life development, since early-life castration has the strongest effects on lifespan. Health in later life is also increased by castration in laboratory rodents," Garratt said.

For females, a broader range of sterilisation methods improved survival.

“In females, lifespan increases after several different forms of sterilisation, suggesting that benefits arise from reducing the substantial energetic and physiological costs of pregnancy, lactation and caring for offspring, rather than from a single hormonal mechanism,” he said.

The findings were published in the journal Nature and include analysis from 117 species, plus a meta-analysis of other vertebrate studies.

The extra years of life weren’t trivial, either.

Depending on when sterilisation occurred and the environment the animal experienced, life expectancy rose by 10–20%.

Co-author Fernando Colchero, of the Department of Primate Behaviour and Evolution at Germany’s Max Planck Institute for Evolutionary Anthropology, said the results reflect how heavily reproduction weighs on survival.

“Reproduction is inherently costly, although environments can soften or exaggerate these costs, particularly human environments, which can buffer or modify them thanks to healthcare, nutrition and social safety.”

The study also found differences in how animals lived longer.

For males, sterilisation reduced deaths linked to aggression and risk-taking.

For females, it lowered deaths from infection and infectious disease, likely because the energy demands of reproduction weaken immunity.

Garratt said the research lends support to the evolutionary advantage of menopause.

“Unlike in males, we found no evidence that the effects of contraception on survival are dependent on the timing of sterilisation, so not reproducing in later adulthood, even after already producing some offspring, might provide later-life survival benefits in females.

“However, while lifespan was increased by a range of sterilisation approaches, in the case of ovary removal, which also removes ovarian hormone production, aspects of health in later life are impaired.

“These findings on lifespan and healthspan shed light on the health-survival paradox observed in post-menopausal women, who outlive men on average but suffer increased frailty and poorer overall health during ageing.”

Ben Tomsett is a multimedia journalist based in Dunedin. He joined the Herald in 2023.