Researchers here mine human data and records from zoos to show that male castration and female sterilization increase life span in a very broad range of higher animals. Mechanisms are thought to be similar from species to species, even if the size of the effect on life span varies. In males, it appears largely connected with systemic effects of exposure to androgen hormones over a lifespan, while in females it appears largely connected to stresses resulting from reproduction. Thus in males only hormone level reduction increases life span, while in females any contraceptive approach that prevents reproduction increases life span.
Our results demonstrate that ongoing hormonal contraception and permanent methods of surgical sterilization increase vertebrate survivorship. The analysis of zoo records provides unparalleled insight into the taxonomic breadth of the lifespan response, with male castration, female surgical sterilization and ongoing female hormonal contraception linked to increased life expectancy across a broad range of species within the mammalian kingdom.
Life expectancy is increased by an average of 10-20% depending on the timing of treatment and environment the animal is exposed to, providing strong evidence for the presence of an intraspecific trade-off between adult reproduction and survival in vertebrates. Notably, however, we do not observe the very substantial, often more than 50% increases in lifespan that are observed in some invertebrate species after germ cell removal, particularly in species that are semelparous.
There is a wide species-level heterogeneity in the survival response to sterilization and contraception. What causes this remains to be determined. It has been widely hypothesized that male gonadal-specific hormone production (testosterone) contributes to shorter lifespans in males relative to females. In rodents, castration is associated with improvements in several domains of health in later life, in particular cognition and physical function. Thus, reducing male androgen signalling may broadly target multiple processes involved in the biology of ageing.
In females, increased life expectancy occurred with various contraceptive methods. Contraception reduced the risk of death from multiple causes, including infectious and non-infectious diseases. We hypothesize that the increased life expectancy in females arises from reduced allocation to reproduction and reproductive processes in adulthood, with contraception strongly reducing the direct and indirect costs of offspring production.
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