The eunuch group also boasted three centenarians among the 81 verified life spans, an unusual number considering that the current incidence of centenarians is just one in 3,500 in Japan and one in 4,400 in the United States.
"I thought there were errors in our data and checked everything again," Min says. "I was quite surprised by the big difference in longevity and the number of centenarians."
The study doesn't directly explain why the eunuchs lived so much longer, but it provides the strongest evidence yet that testosterone — the key difference between the eunuchs and their peers in this study and a proxy for the difference between women and men — plays a role, says Steven Austad, a biogerontologist at the University of Texas Health Science Center in San Antonio, who was not involved in Min's study.
"This is the most thorough, well-controlled study of its kind," Austad says. "The sex difference in aging and longevity is an almost unexplored area, and this study highlights that testosterone is part of the issue."
Identifying all the factors that contribute to the difference in longevity between men and women may help researchers find ways to temper their effects, Austad says. That, in turn, could help men live longer — without losing any body parts in the process.
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This article was produced by ScienceNOW, the daily online news service of the journal Science.