Want to live to 100? A new study suggests that, for men, your testicles might be holding you back.
Korean eunuchs — men who had their testicles removed — outlived their contemporaries by as many as 14 to 19 years, suggesting that male sex hormones somehow act to shorten the male human lifespan, according to a new historical study of records spanning from the 14th century through the early 19th century.
The finding, reported Monday in the journal Current Biology, argues for something called the “disposable soma theory.” The idea is that since animals have limited access to energy, there is a natural trade-off between reproduction and the maintenance of the body’s cells.
But evidence for the theory has been limited, and some strong counter-evidence exists: Numerous studies in mammals have shown that restricting caloric intake can lengthen the lifespan of some animals — though sometimes such animals become infertile, a fact that may favor the disposable soma hypothesis.
If the theory were true, South Korean researchers figured that it could be seen in humans by looking at the production and circulation of male sex hormones. That makes eunuchs a nice group to study, since the testicles are responsible for much of that work.
The study authors used an historical document from the early 19th century called the Yang-Se-Gye-Bo, which is a genealogy of eunuchs who worked in the palace and served the nation’s royalty. The researchers were able to identify 81 eunuchs in the document for whom they could identify birth and death dates. Then they cross-referenced the information with other historical Korean documents, including the Annals of the Chosun Dynasty, to ensure the data were accurate.
They found that the eunuchs lived to be around 70 years old on average, while non-eunuchs who lived alongside them with similar social and economic status lived to be between 50 and 55 years old — a difference that was striking and unlikely to be due to chance.
The researchers use the finding to explain another common observation: The fact that women generally live longer than men, which they say may be because women lack the same quantities of hormones like testosterone.
While it is possible that working in the royal palace contributed to the eunuchs’ longevity, the researchers did their best to control for this by comparing them to men in the royal family, who, according to the Annals of the Chosun Dynasty, rarely made it to 50 years of age.
The small group of eunuchs studied included three centenarians — well above the statistical averages seen today across the developed world. Japan has only one centenarian for every 3,500 people; the U.S. has one in 4,000, according to the study.
The evidence is compelling that the eunuchs lived substantially longer than their peers. But any biological explanation remains hard to confirm, in part because it is impossible to know whether other aspects of their lifestyle — including potential dietary choices or physical exercise — might have contributed to their longevity.
So while it is clear that something about the eunuchs allowed them to live long lives, it remains to be determined whether it was their lack of testicles alone.
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