Richard G. Bribiescas is a professor of anthropology and evolutionary biology at Yale University and his new book is the best short summation I have seen of a massive body of scientific research to address his title subject, How Men Age. Now that I am in my early 60s I find myself gravitating toward this literature, but this is not a how-to book. There is no men’s magazine-style bullet list of what older men should do to look and be young again. Bribiescas is a good scientist, and as such he makes it clear that all such studies are limited in scope, have exceptions, and the long-term consequences of any artificial interference with the aging process beyond diet and exercise are unknown. Caveat emptor! Here is what we know.
Aging is the decline in physiological function that occurs over a measurable passage of time, caused by a combination of physics, genes, disease, and other environmental assaults and stressors. Aging is highly heritable, which is why physicians and life insurance companies always ask about the age of your parents at death and the causes of their deaths. But there is no “gene for aging,” or even a suite of genes. Aging happens across most of the systems in your body and there’s only so much you can do to stave off its inevitable effects. Worse, tinkering with the aging process too much can lead to a phenomenon the biologist G. C. Williams discovered called antagonistic pleiotropy—traits beneficial to an organism early in its life may be detrimental later in life, such as women’s high ovarian steroid levels during peak reproductive age that can lead to breast cancer decades later, or high testosterone in young men that leads to prostate cancer in old age. So the idea of taking testosterone supplements to ward off aging’s effects may have unintended and possibly antagonistic pleiotropic effects that lead to even earlier mortality.
According to “rate of living theory,” larger mammals conserve heat more efficiently, have slower metabolic rates, burn energy slower, and live longer. Humans are relatively large mammals and we live longer than any other primate, but within our species even though men are larger than women they burn more energy per unit time, so men age faster than women and women live longer than men. As well, because the world is a dangerous place and men face many more risks than women, they tend to discount the future and reproduce earlier, just in case.
Environment also makes a difference. The evolutionary biologist Steven Austad conducted a study of opossum populations, one on an island with no predators and the other on the mainland with the usual assortment of threats to life and limb. Austad found that the island opossums reproduced later and aged slower whereas the mainland opossums reproduced sooner and aged faster.
What about human populations? Bribiescas has conducted research on the traditional hunter-gatherer Aché people of Paraguay, where he has witnessed many young girls age rapidly once they started having children. Why? Entropy. “The daily grind of activities necessary to care for a family surely contributes to their physical decline.” At his lab at Yale University, Bribiescas’s research group hypothesized “that women who have more children will exhibit physiological signs of accelerated aging,” and they tested this hypothesis on a group of rural postmenopausal Polish women who were part of a long-term study on women’s health by the University of Krakow. The researchers found that women with more children had significantly higher levels of oxidative stress compared to those who had fewer children, which is revealing because oxidative stress is one of the key physiological markers of genetic, cellular, and tissue damage associated with aging in all organisms.
Men don’t suffer such reproductive costs, but their aging comes from other assaults on their bodies as a result of competing for women and resources. It’s a cost-benefit trade-off argument: “a male who engages in a behavior or invests in metabolic processes that increase his present mortality risk by 1 percent but also promotes his probability of mating opportunities will have potentially greater fitness benefits compared to a female who engages in the same risk and mating benefit since access to more than one mate will not increase a female’s fitness.”
Among the many activities that leads to earlier mortality for men are the stupid things they do to win the affections of females and gain status among their fellow males. “Men are willing to bet a stack of survivorship chips if the big payout is the possibility of sex,” Bribiescas avers. Studies in the evolutionary psychology of mating strategies show that young women tend to prefer men who engage in risky behavior—the risk taking being a “costly signal” that indicates to a female that a male’s genes are so good he can afford to take such risks. Men smoke, drink, gamble and partake in risky sports more than women, and are less likely to seek medical attention when ill.
There’s another type of fitness beyond evolutionary, and that is physical. Getting a handle on men’s love handles is one Bribiescas addresses in discussing aging and the metabolism of men. Why do we have them? Humans are sexually dimorphic, which means that men and women differ in size and strength, the most common difference involving muscle mass and tone. Human hunters don’t have awesome claws, fangs, or antlers, but we have upper-body strength and we can throw projectiles, the capacity for which appears to have evolved in humans (but not as much in chimps and other primates) around the time that hunting developed in human history.
Declines in testosterone, lower metabolic rates, and shifts in the hypothalamic-pituitary-testicular (HPT) hormone axis is what ultimately makes men go soft in the middle. Testosterone levels peak in the second decade of life, decline until around age 40, and remain stable thereafter. Encouragingly, Bribiescas cites a study by endocrinologists in which younger men (age 19–35) and older men (age 60–75) were given testosterone supplementation (controlled for natural background rate differences) that found “increases in overall fat-free mass, muscle growth, and strength to graded doses were not significantly different between younger and older men.” Both age cohorts responded positively, and in fact “older men exhibited significantly higher testosterone levels in response to each graded dose compared to younger men.” Meaning? “Younger men may have more efficient liver and kidney function, resulting in higher clearance rates, or, more interestingly, there may be differences in hypothalamic function in response to testosterone.”
This would seem to confirm the in-flight magazine ad for anabolic hormone therapy for men featuring the older physician with the young buff body, but Bribiescas cautions that he is “not aware of any clinical studies indicating that this therapy regimen is safe.” Nevertheless, he continues, “other clinical studies strongly suggest that men can improve strength and vigor with hormones.” So why don’t our bodies do this naturally? It’s the trade-off problem again. Fueling all that extra muscle is expensive, and evolution probably selected for a shift in investment costs over time—older men don’t need as much muscle because they are putting their valuable resources elsewhere, and “muscle-induced increases in metabolic rate can tax the limits of other organs such as the heart, liver, and kidneys.” I.e., there’s no free lunch. There are trade-offs at every stage of life. You want your 25-year old body back at 75? You can have it but you are going to pay a price somewhere, and we do not yet fully know what that price might be.
We do know one penalty men pay for having a higher metabolic rate than women: shorter lives. The best study on the relationship between basal metabolic rate (BMR) and mortality is the Baltimore Men’s Study on 972 men over 40 years that found BMR declined with age, but in men with naturally higher BMR their mortality increased. Specifically, compared to a younger age group, elevated BMR in men age 33.9–36.4 was 28 percent higher, and in men 36.5 or older mortality increased 53 percent, although Bribiescas cautions that “this study raises the question of why some men have higher BMR than others.” There may be intervening variables not yet determined.
More trade-offs: taking testosterone supplements may lead to fat loss and muscle bulk and strength, not to mention making you feel virile and strong again, but there is some evidence that taking testosterone supplements may lead to a serious myocardial infarction within a few weeks, compared to men not taking the hormone. It may also suppress immune function, not to mention the well-known effect that high testosterone men are more likely to engage in risky behaviors that have their own mortality risks. In the end, Bribiescas concludes in this book that should be read by all men age 50 and older (and young men who hope to grow old), “As anyone who has had one martini too many can tell you, feeling good does not necessarily mean you are engaging in healthy behavior.”
Michael Shermer is the publisher of Skeptic magazine, a monthly columnist for Scientific American, and a Presidential Fellow at Chapman University. His book The Moral Arc is now out in paperback. Follow him on Twitter @michaelshermer.