Men, what would you be willing to give up to live a couple decades longer? Think carefully before you answer. Research has shown that men who are castrated may have significantly longer lifespans. Here's what we know.

Photo Credit: Colby Stopa via flickr | CC BY 2.0

Behavior or Biology?

You've probably heard about the gender gap in human life expectancy. According to the United Nations Department of Economic and Social Affairs, females worldwide live an average of 73.5 years, while males average 68.5. Those figures can vary pretty drastically (life expectancy for both men and women is still less than 55 years throughout much of sub-Saharan Africa), but the last several decades have seen large gains in life expectancy across the globe, for men and women, alike. Still, the gender gap persists*. "Wherever they live in the world," reported the World Health Organization in 2014, "women live longer than men."

Why the disparity? It's tempting to pin the blame on social and behavioral differences. Consider, for example, that 82% of people killed by lightning are male. Now, is there something about the male biology that makes it more attractive to bolts of electricity, or are men just more likely to engage in behavior that'll get them zapped? The National Oceanic and Atmospheric Administration, for its part, thinks it's the latter:

Possible explanations for this finding are that males are unaware of all the dangers associated with lightning, are more likely to be in vulnerable situations, are unwilling to be inconvenienced by the threat of lightning, are in situations that make it difficult to get to a safe place in a timely manner, don't react quickly to the lightning threat, or any combination of these explanations.

This pattern of male fatalities exceeding female ones holds, elsewhere. The Insurance Institute for Highway Safety reports that "more men than women die each year in motor vehicle crashes," with the former logging more miles and engaging in riskier driving practices than the latter; and the U.S. Department of Labor reports that, in 2013, male fatalities accounted for a staggering 93% of occupational deaths in the United States.

Castration's Questionable Life-Prolonging Effects

What none of these demographics point to is a clear biological basis for men's shorter lifespans. In the late sixties, however, results from a study conducted by researchers James Hamilton and Gordon Mestler seemed to provide exactly that. The Straight Dope's Cecil Adams provides a tidy summary of their investigation, the findings of which are published in 1969 issue of The Journal of Gerontology:

[Hamilton and Mestler] compared the lifespans of 297 castrated inmates at a Kansas institution for the mentally retarded with those of 735 intact males at the same facility. The castrated males had gone under the knife at ages from 8 to 59 years old, with the average age ranging from 12 (!) in 1898 to 30 in 1923. They didn't vary markedly from intact inmates in terms of IQ, type of mental disability, and so on, suggesting there had been no firm criteria for the operation other than possibly your getting on the hospital staff's nerves — too bad if you were an inmate but lucky for science, since except for castration the two groups were indistinguishable.

Result: the castrated inmates on average lived 13.6 years longer than the intact ones (55.7 vs 69.3 years). What's more, the earlier you were castrated, the longer you lived.

The findings suggested that one side-effect of testosterone may be an abbreviated lifespan, and that curbing the sex hormone's release could help males live longer. Hamilton and Mestler hypothesized that testosterone's ill-effects, and the life-prolonging benefits of castration, applied to males of all species, due in large part to a wideheld belief that castrated animals live longer than their intact counterparts. But the evidence for these assumptions is rather ambiguous.

While there seems to be some consensus that the females of most species live longer than males, a 2010 evaluation of the risks and benefits of neutering dogs and cats pokes holes in the idea that sex hormones are to blame, by reporting that "no firm conclusions can be drawn about the effect of neutering on longevity." One notable exception is a study that found neutering to prolong the lives of Rottweilers, but the fact that neutered females lived longer than their male counterparts confounds things, by suggesting that sex hormones broadly – as opposed to testosterone, specifically – may be responsible for shortened lifespans.

The upshot? It's complicated! A recent investigation into lifespan and aging in Drosophila simulans (an important model organism in speciation research that is closely related to the ubiquitous D. melanogaster) highlights how confusing things can get, when considering the effects of natural and sexual selection – both of which depend on behavioral and social factors – on the evolution of aging and lifespan. Taken together, the authors write, sex-specific effects of sexual selection (i.e. how successful members of a species are at securing and reproducing with mates) and natural selection "may help explain the diverse patterns of aging seen in nature, but complicate predictions about how aging and life span evolve across the sexes."

More Contradicting Evidence

The most recent study I could find on the subject of human castration's longevity boosting effects in humans was "The Lifespan of Korean Eunuchs," a straightforwardly titled investigation performed by Korean scientists Kyung-Jin Min, Cheol0-Koo Lee, and Han-Nam Park, and published in a 2012 issue of Current Biology.

Min and his colleagues studied the genealogical records of 81 Korean eunuchs born between 1556 and 1861. (Historically, Korean royalty relied on eunuchs to guard the gates, manage food, etc., and were the only men outside the royal family permitted to spend the night inside the palace walls.) The average lifespan of eunuchs was found to be 70 years of age (the records also made note of three centenarian eunuchs, including a 109-year-old), 14.4- to 19.1-years longer than the lifespan of non-castrated men of comparable social standing.

Min told the BBC at the time: "We also thought that different living circumstances or lifestyles of eunuchs can be attributed to the lifespan difference... However, except for a few eunuchs, most lived outside the palace and spent time inside the palace only when they were on duty." Instead, the researchers conclude their study "provides compelling evidence that male sex hormone reduces male lifespan."

Evidence is not always proof, however, and other experts emphasize this fact. "It may not have anything to do with being eunuchs," said S. Jay Olshansky, a professor of public health at the University of Illinois in Chicago who studies longevity, at the time. Similarly, a small, unpublished study of 25 documented castrati born between 1610 and 1762 seems to contradict the Korean eunuch study. Researcher J.S. Jenkins found the average lifespan of the castrated group to be similar to that of 25 intact male singers born during a similar period. "The relative longevity for this period may be explained by the fact that both groups lived fairly cosseted lives," Jenkins writes.

All that being said: If you're a man, and you're considering taking drastic measures to extend your lifespan, you should know that everyone seems to agree that castration is not the answer. "I would not recommend becoming a eunuch," says Dr. L. Stephen Coles, a co-founder of the Los Angeles Gerontology Research Group. Taking drugs to reduce your sex hormones is also a bad idea, he says, pushing the quality v. quantity of life angle, adding that this could have undesirable side-effects, e.g. severely diminishing one's sex drive.

Min and the other authors of the Korean eunuch study, agree. There are less drastic ways to extend one's life. Smoke less. Eat better. Exercise more. You know, the usual. "For better health and longevity," they write, "stay away from stresses and learn what you can from women."

You can start by staying inside during lightning storms.

*It is true that, in many countries (the U.S. included), that gap is narrowing; and there are, of course, some striking geopolitical outliers (in Japan, the average male life expectancy of 85 years exceeds the average female life expectancies of all but eleven countries) – but on a country-by-country basis, women still dominate the long game.