Where Has All the Testosterone Gone?
· The Atlantic
The Trump administration seems to harbor a hulking obsession with testosterone. Health Secretary Robert F. Kennedy Jr. once claimed that the president’s testosterone levels are unusually high for a man of his age, and Kennedy is known to take a supplementary dose of the male sex hormone himself. In April, the FDA moved to expand access to testosterone-replacement therapy for greater numbers of men. And last month, Defense Secretary Pete Hegseth announced that “warfighters” older than 30 will have their testosterone levels checked annually so that they can stay on the “leading edge of lethality.”
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The need for expansive testing or for testosterone replacement is questionable, according to several medical experts I spoke with. But underneath the administration’s preoccupation lies a real trend: Although most men’s levels are still within the normal range, average testosterone has been declining among men for the past several decades. A recent review of studies involving more than a million men all over the world found that average testosterone levels in blood have dropped by about 20 percent over the past half century. A new, unpublished study put the decrease during that basic time period at closer to 50 percent. Some scientists are skeptical of these numbers because testosterone has been measured in different ways over time. But Michael Eisenberg, a urologist at Stanford Medicine who specializes in male fertility, told me that the findings of a decline are “pretty solid.” The testosterone slump, he said, has “manifested across many different study designs.”
Medical researchers aren’t certain what’s causing the drop. The global population is aging, and men’s testosterone levels go down naturally as they get older—but this can’t account for the change, because most studies control for age. One theory is that the environment is playing a role: John Meeker, an environmental-health professor at the University of Michigan, pointed to endocrine-disrupting “forever chemicals,” such as the phthalates in our plastic kitchen utensils and the PFAS in our nonstick pans. These chemicals can interrupt both the creation and the activity of testosterone in the body.
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Lifestyle shifts seem to be a big part of the story. “Our population is less well than it was decades ago,” Richard J. Fantus, a urologist at the University of Kansas, told me. Manual laborers, whose ranks have decreased over time, have more testosterone than men whose jobs are less physically demanding, and some men who are very physically active are less likely to have clinically low testosterone. Obesity, a condition that about 14 percent of men around the world have, can suppress the hormone. Fat tissue contains high amounts of an enzyme that converts testosterone into estrogen, and excess fat can overheat the testes. When obese men lose weight, including through the use of GLP-1s, Fantus told me, their testosterone levels tend to go up.
Obesity can’t explain the entire decrease, however. One large-scale, recent review found a testosterone slump despite researchers’ adjusting for the subjects’ body mass index. “Even among normal-weight men, we see that same decline,” Eisenberg said. Some analyses, he added, have suggested that testosterone has dropped off most profoundly among normal-weight men. Some other broad societal shifts, meanwhile, have not seemed to affect testosterone in expected ways: Fathers and men with long-term romantic partners have lower testosterone than single and childless men—but even as marriage and fertility rates have slowed in many parts of the world, testosterone levels have continued dropping.
Whatever the cause, the decline is somewhat worrisome because testosterone is important for mood, sexual function, and energy levels, as well as muscle, heart, and bone health. Men whose testosterone levels are too low might struggle with decreased sex drive, fatigue, depression, or muscle loss. Testosterone is needed for sperm production, so low testosterone might impair fertility too. More philosophically, the drop is just kind of strange: Why would an essential hormone suddenly fade away? “It’s kind of frightening,” Eisenberg said, “to think that there’s something that is fundamentally changing our biology.”
What to do about this problem, however, is far from obvious. On a societal level, unwinding dependence on forever chemicals, eliminating obesity, or reversing the trend toward office jobs would be nearly impossible. On an individual level, men who suspect that they have low testosterone can get lab tests. But if they do turn out to have low levels, whether they should pursue treatment is unclear. For men with low levels, testosterone supplements have been shown to improve mood and increase bone density, red-blood-cell count, and interest in sex. But unlike the testosterone the body naturally makes, supplements can paradoxically decrease sperm count, and a man who wants to have kids may want to avoid them for that reason. In addition, Fantus told me, supplementing with testosterone might raise the hormone’s levels but not alleviate symptoms.
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One approach that most experts I spoke with agreed was unnecessary: widespread monitoring of the sort that Hegseth has proposed for the military. For the 90,000-some female service members older than 30, the policy is useless—testing women for insufficient testosterone is never recommended. For men—especially those without symptoms—the Endocrine Society cautions against broad testing. Peter J. Snyder, an endocrinologist at the University of Pennsylvania who led a major study called the “Testosterone Trials,” told me that to find 800 participants who qualified as having low testosterone, he and his colleagues had to screen more than 50,000 men. “It was harder to get into the Testosterone Trials than to get into the University of Pennsylvania medical school,” he said.
A regimen such as the one the Defense Department is pursuing, Snyder told me, has a higher chance of surfacing false-positive results than accurate ones. Fantus said that broadly screening for low testosterone would mean “we would be overdiagnosing”—which could also lead to overtreating. Hegseth has said that testosterone supplements would be optional, but presumably many service members who receive a low reading might feel pressure to use them.
Perhaps it’s a mistake to see low testosterone as a sickness urgently in need of a cure, when the dip may simply be a marker of modernity. Altered hormones, along with eyestrain and belly paunch, could be part of the price we pay for material comforts. The testosterone dip, in other words, might be a bellwether—another sign that contemporary life is changing humans in ways we are only beginning to recognize.