A Nature study analyzing 117 captive mammal species and a broader meta-analysis found that sterilization increased life expectancy by nearly 18% on average. Effects depended on sex, timing and method: prepubertal castration extended male lifespan, while vasectomy did not, implicating loss of testicular hormones. In females, contraception often improved longevity by reducing the energetic costs of pregnancy and lactation, though ovary removal raised frailty despite longer life. Historical human data on castration showed a similar average lifespan increase, but limitations and confounders warrant cautious interpretation.
Does Skipping Reproduction Add Years to Life? New Study Links Sterilization and Longevity
Lead image: Reto Buehler / Shutterstock
Biologists have long recognized a trade-off between reproduction and longevity: organisms have finite metabolic energy, and how that energy is allocated can influence lifespan. A new study published in Nature provides strong evidence that this trade-off operates not only across species but also within individual animals.
What the Study Did
Researchers from the University of Otago–Ōtākou Whakaihu Waka (New Zealand) and collaborators analyzed records for 117 species of captive mammals from zoos and aquariums and performed a broader meta-analysis of other vertebrate studies. They restricted the core analysis to species with at least 30 documented individuals of each sex, then compared survival statistics for animals that had undergone sterilization (permanent or long-term) with those that had not.
Key Findings
Across species, sterilization increased life expectancy by nearly 18% on average. However, effects varied with sex, timing and sterilization method, and with animal-care and demographic factors.
Males: Castration (removal of the testes) extended lifespan, particularly when done before puberty. By contrast, vasectomy—which renders males infertile without removing the testes—did not extend life. This pattern implicates the removal of testicular hormones (for example, testosterone) rather than infertility per se as a driver of increased longevity in males.
“These hormones may interact with pathways that regulate the biology of aging, particularly during early-life development, since early-life castration has the strongest effects on lifespan,” said co-author Mike Garratt, a reproductive biologist at the University of Otago.
Behavioral changes likely contribute as well: castrated males often show reduced aggression and mate-competition behavior, which can lower the risk of injury and stress-related mortality.
Females: Various contraceptive interventions were generally associated with increased longevity. The authors attribute this to savings in the energetic and physiological costs of pregnancy, lactation and parental care. Females treated with hormonal contraceptives also showed indicators of more robust immune function, suggesting some of the energetic savings may bolster disease resistance.
Females that stopped reproducing after raising offspring also benefited in lifespan, a result that supports evolutionary ideas about the advantages of reduced later-life reproduction (often discussed in relation to menopause). However, there was an important caveat: permanent surgical removal of ovaries (ovariectomy) produced increased lifespan in some cases but was also associated with greater frailty and compromised health, likely because ovarian hormones support other aspects of physiology.
Humans and Limitations
The team also reviewed historical human studies of castration. Although those epidemiological results were mixed, pooled analyses showed an average lifespan increase in castrated men similar to the animal data—around 18%. The authors caution, though, that human results are retrospective and subject to confounding factors.
Important limitations apply to the animal work as well: the data come primarily from captive animals, where medical care, diet and social conditions differ from the wild. Observational and historical datasets can be affected by selection biases and unmeasured confounders, and associations do not prove direct causation. Still, the consistency of the patterns across species and study types strengthens the evidence that reproductive biology and sex hormones play major roles in aging trajectories.
What This Means
The study highlights how energy allocation, hormones and behavior combine to link reproduction and longevity. It suggests that suppressing reproduction—by altering hormones or reproductive effort—can shift physiological investment toward maintenance and survival, but the health trade-offs depend on sex, method and timing. These results deepen our understanding of life-history trade-offs and point to hormone-related pathways as promising targets for aging research, with careful attention to healthspan as well as lifespan.
Note: The findings do not imply simple prescriptions for humans. Differences between captive animal populations and humans, plus the complex roles of sex hormones in overall health, mean medical or ethical implications require cautious interpretation and further research.
