Castration increases the lifespan of males in many mammalian species, including humans. However, a new study has revealed an unexpected finding: the procedure does not necessarily need to be performed at a young age to extend life, as was previously believed. The researchers report that removing the testes of adult male mice increased their lifespans by more than 30%. This challenges long-held views regarding the role of the testes in the aging process.
If the underlying mechanism can be uncovered, it may become possible to develop a therapy that offers the same benefits as castration—without the need for surgery.
In humans, females live significantly longer than males. Men are more susceptible to almost all age-related diseases, including cancer and heart disease. This female longevity advantage is one of the most consistent features of human biology.
While the exact causes remain unclear, there is compelling evidence that the testes themselves may be detrimental to males. A 1969 study of individuals with intellectual disabilities in a psychiatric institution—who had been subjected to forced castration—suggested that the removal of the sex glands could extend life by more than a decade. Furthermore, a 2025 analysis covering 22 vertebrate species identified a consistent link between castration and increased longevity.
Studying this effect in laboratory mice is complex, as the lifespan gap between males and females varies by genetic strain—in some strains, males actually live longer than females. In a 2023 study, biogerontologist James Nelson and his colleagues at the University of Texas Health Science Center at San Antonio utilized a strain in which females consistently lived longer than males—a pattern similar to that seen in humans. When the males were castrated before reaching sexual maturity, they lived nearly as long as the females. This suggested that the testes, in one way or another, shorten one’s lifespan.
In a new study, Nelson, his graduate student Laurence Maeyens, and their colleagues set out to determine at what age the testes begin to have a detrimental effect. They castrated male mice from the same strain, dividing them into three groups: those castrated before puberty, shortly after puberty, and on the 240th day of life—an age roughly equivalent to 30 years in humans. All three groups lived longer than the control animals, which had undergone a sham surgery (a procedure that mimicked the operation but left the testes intact).
The greatest increase in lifespan was observed in the mice castrated during adulthood: they lived approximately 33% longer than the control group. For the animals that underwent the procedure before or shortly after puberty, lifespans increased by 19% and 26%, respectively. This finding came as a surprise to the researchers.
In the adult mice, the effect became apparent almost immediately following the removal of the testes. Not a single animal from this group died within the year following the surgery—a particularly notable outcome, given that the mortality rate for mice typically rises sharply at that age. The authors suggest that the testes may begin to harm the body in later life, whereas in youth, their presence might actually promote longevity.
Why the mice castrated on the 240th day lived longer than the others remains a mystery. Furthermore, as they aged, these mice did not appear physically stronger than the other animals; in all three castrated groups, grip strength declined at the same rate, and other signs of aging emerged at a similar pace.
To gain further insight, the researchers plan to examine the organs of the castrated mice to identify the specific health issues that led to their deaths. Additionally, the scientists hope to identify substances produced by the testes that may influence lifespan. These organs produce more than 90% of the testosterone in the body, but it is too early to claim that this specific hormone accounts for the observed patterns.
If the factors determining the difference in lifespan can be identified, it could lead to the development of so-called “castration mimetics”—agents that replicate the longevity-promoting effects of removing the testes. Such interventions might prove effective even in old age. However, researchers caution that it is far too soon to extrapolate these experimental findings to humans.
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