But the longevity gap isn't solely restricted to humans. Female members of the animal kingdom also commonly live longer than their male counterparts. For example, female chimps live about 14 years longer, female orcas about 30 years longer, and female sea lions 12 years longer.
Such a universal disparity in longevity likely suggests that a fundamental difference between the sexes is to blame. Mutations in mitochondria -- the cell's powerhouse's -- have recently been implicated. Men also may simply be more "disposable" (in a biological sense, of course). But the likeliest culprit is the very hormone that defines masculinity: testosterone.
Primarily secreted in sex organs, testosterone is the principal male sex hormone and is essential to male functioning and well-being. Each day, men produce about twenty times more of it than women do. But while testosterone defines manhood, it may also get men killed.
Commonly thought to promote both aggression and risky behavior, testosterone is often implicated as the driver behind the glaring male-female mortality gap among twenty-somethings, an age demographic where men are two-and-a-half times more likely to die than women. Because of young men's proclivity to undertake risky behaviors in their twenties -- activities like binge drinking, fighting, and general acts of stupidity (apparently meant to showcase virility) -- this time is often labeled the "Testosterone Storm."
Testosterone-fueled risk-taking may persist even later in life. In 1999, a sweeping analysis of the link between testosterone and men's health was published in the Journal of Behavioral Medicine. Researchers interviewed and examined 4,393 men, and discerned good and bad news for guys' favorite hormone.
Men with testosterone levels slightly above average were less likely to have high blood pressure, less likely to experience a heart attack, and less likely to be obese. However, men with higher testosterone levels were more likely to report one or more injuries, more likely to consume five or more alcoholic drinks in a day, more likely to have had a sexually transmitted infection, and more likely to smoke.
"Analysis revealed that having a high level of testosterone, compared to a low level, increased the odds of health risk behavior," the authors reported.
Strong Libido, Weak Immune System?
Testosterone seems to be a double-edged sword. While it appears to enhance mating success, it also may reduce the strength of the immune system.
"When testosterone is lacking, the demand for amino acids to support cell proliferation and muscle-building is decreased, and it's thought that the body then shifts the use of these basic building blocks towards cellular defense and stress resistance," gerontologist Holly Brown-Borg told NewScientist.
Excessive testosterone appears to lead to adverse health consequences and reduced lifespan, but does this mean that cutting the hormone almost completely out of the equation bodes an opposite, positive outcome? A study published last year, which followed Korean eunuchs living between the mid-16th and mid-19th centuries, found that they lived 14 to 19 years longer than their non-castrated counterparts.
Worldwide, testosterone levels appear to be falling, and many bemoan the end of masculinity. There is, however, a silver lining to this reduction in macho-ness: men appear to be narrowing the gender gap with women.
Testosterone is the sword that men live by and die by. If the blade dulls, men may very well live longer.
(Image: Macho Man via Shutterstock)