We were very surprised to find the large difference. The incidence of centenarians was what surprised us most; out of 81 eunuchs, three lived for more than 100 years.
Professor Kyung-Jin Min
Research which has appeared today in the Cell Press publication Current Biology
suggests that castrated men outlived other men during the years of Chosun dynasty in Korea by a significant margin. The study adds weight to the argument that male sex hormones could be responsible for shortening men’s lives and for creating the discrepancy in expected lifespan between men and women.
Kyung-Jin Min, Associate Professor in the Department of Natural Medical Sciences at Inha University in South Korea, took the time to expound on the research findings to ScienceOmega.com
in more detail. He began by setting out what prompted him and his colleagues to carry out the study.
"It is well-known that castration extends lifespan in many mammalian species," Professor Min explained. "However, there are limited studies which come to different conclusions regarding the effects of castration on lifespan in humans. We thought that measuring the lifespan of Korean eunuchs could nail down the unsolved question."
The study was based on the analysis of detailed genealogical records of eunuchs from the Imperial court of the Korean Chosun dynasty, which ruled from 1392 AD to 1910. In the court, eunuchs were allowed to marry and carried on their lines by adopting girls and castrated boys. Although the members would not have been blood-related, it is believed the ties formed within these families were often as strong as those in blood-related families.
Along with his colleague Cheol-Koo Lee of Korea University, Professor Min found from studying the records that the lifespan of eunuchs was considerably longer than that of non-castrated males of similar socio-economic status; they lived 14 to 19 years longer. I asked Professor Min if they were surprised to find such a large difference between the average lifespan of eunuchs and other men in the Korean Imperial court.
"We were very surprised to find the large difference," he said. "The incidence of centenarians was what surprised us most; out of 81 eunuchs, three lived for more than 100 years."
Even by modern standards these figures are remarkable. Given that only one in 4400 Americans and one in 3500 Japanese citizens live to 100, the incidence of centenarians among the eunuchs is 130 times greater than in present day, developed societies. The team believes their evidence is conclusive that the privileges and benefits of high socio-economic status alone cannot account for this significant difference in longevity.
"We wanted to check whether lifestyle had affected the results," Professor Min remarked. "However, the eunuchs did not live inside the palace. Except for a few, most had their home outside the palace and would only spend the night inside the palace when on duty.
"We also checked the lifespan of kings and male royal family members to see whether the lifestyle experienced inside the palace could have affected the results. The average lifespan of kings and royal family members was still significantly lower than that of eunuchs."
I asked Professor Min how he and his colleagues think the difference could be explained.
"The male sex hormone, testosterone, could explain the difference," he answered. "Testosterone is known to reduce immune function and increase the incidence of coronary heart disease. Castration shuts off the production of testosterone and, it seems, must boost immune function and decrease the incidence of heart disease."
It has been hypothesised – in the disposable soma theory – that cells in the rest of the body go unrepaired as resources are competitively allocated to reproduction. The results of the study seem to uphold this idea, and the researchers intend to investigate the lifespan of eunuchs in other cultures, such as the Chinese and Ottoman empires, to further explore the effects of the male sex hormone on ageing.