Castration can increase a man's lifespan by up to almost 20 years, a study of eunuchs has shown.
Scientists analysed genealogy records of members of the Korean imperial court dating from 1392 to 1910.
The records were kept as proof that people belonged to the noble class. They included information about eunuchs, who either lost their reproductive organs in accidents or underwent castration to gain early access to the palace.
The noble Korean eunuchs lived 14 to 19 years longer than men of similar social class who were "intact".
Among 81 eunuchs studied, three lived to 100 or more. The average eunuch lifespan was 70 years, compared with 60 to 56 for non-eunuch men in the court.
Centenarians were at least 130 times more common among the Korean eunuchs than they are in developed countries today, said the researchers.
The finding suggests that male sex hormones, produced in the testes, may be responsible for shortening the lives of men.
In the UK, men today live an average of 78 years and women 82, though the gap is narrowing.
"This discovery adds an important clue for understanding why there is a difference in the expected lifespan between men and women," said lead scientist Dr Kyung-Jin Min, from Inha University in Korea.
The research is reported in the latest issue of the journal, Current Biology.
Eunuchs have historically been employed as guards and servants in harems across the Middle East and Asia.
Several studies have described the long-term effects of castration in eunuchs, but no data on lifespan has been available before.
In the latest research, the longevity of eunuchs was compared with that of men from three non-eunuch families of similar social status in the imperial court of the Korean Chosun Dynasty.
The scientists discounted the theory that palace life contributed to the eunuchs' long lives.
Most of the eunuchs lived outside the palace and only visited it when on duty.
Kings and male members of the Korean royal family, who spent all their time in the palace, also had among the shortest lifespans of all, surviving only to their mid-forties.