Eunuchs - men who were castrated as children - live up to 19 years longer than intact males, according to research by scientists in South Korea.This study, published in Current Biology, was conducted using historical records of more than 385 eunuchs who lived in Korea - where they served the royal family - between 1551 and 1861. From these records, Kyung-Jin Min and his colleagues at Inha University were able to find the dates when 81 of the listed eunuchs were born and died. They found that on average, each lived about 70 years, which is considerably longer than the 50-55 years managed by the equivalent intact man living at the same time. Ironically, this is also far longer than the kings they were serving, who managed, on average, just 47 years!The researchers argue that this difference is likely to be down to hormone levels. Testosterone is mainly produced in the testes, so after castration the amount secreted into the bloodstream falls dramatically. Testosterone might have a negative effect on the immune system, meaning the Eunchs were better protected against infection. It also causes aggression and competitive behaviour in humans and other animals, so it could be that these eunuchs were getting into fewer fights than their un-castrated counterparts and lived less stressful lives. As well as living longer on average, eunuchs were more likely to live to be centenarians; in fact, there were three amongst the 81 individuals the scientists studied. Compared with Japan, where centenarians occur at roughly the rate of one in every 3500 individuals, that makes the Korean eunuchs over 130 times more likely to be a centenarian than average - so there does seem to be something in the idea that reducing testosterone increases lifespan. But we still don't know exactly how this happens, or whether only castration during childhood has the same longevity-enhancing effects. Would a man castrated later in life gain the same advantages? We just don't know.Some critics of the study have also pointed out that no difference in longevity is found when castratos versus non-castrato singers from the same era are compared.A lot more research is needed before we can say for sure that castration will increase your chances of living to 100!