The Trump administration has developed a truly remarkable fixation on testosterone. Health Secretary Robert F. Kennedy Jr. has claimed the president's T-levels are unusually high for a man his age (and he takes a supplement himself). In April, the FDA moved to expand access to testosterone-replacement therapy. And last month, Defense Secretary Pete Hegseth announced that "warfighters" over 30 will get their testosterone checked annually to stay on the "leading edge of lethality."

Medical experts are, shall we say, skeptical about the need for widespread testing or replacement. But beneath the administration's obsession lies a real trend: average testosterone has been declining for decades. A review of studies involving over a million men found average levels have dropped about 20% over the past half century, and a new unpublished study puts the figure closer to 50%. Some scientists question these numbers due to inconsistent measurement methods, but Stanford urologist Michael Eisenberg says the decline is "pretty solid" across many studies.

The cause is unclear. Aging doesn't explain it, since studies control for age. One theory points to endocrine-disrupting "forever chemicals" like phthalates in plastic utensils and PFAS in nonstick pans. Lifestyle shifts play a role: manual laborers have higher T, obesity (affecting about 14% of men globally) suppresses it, and fat tissue converts testosterone to estrogen. But even normal-weight men show the decline, and while fathers and partnered men have lower T, declining marriage and fertility rates haven't reversed the trend.

The drop matters because testosterone affects mood, sexual function, energy, muscle, heart, bone health, and sperm production. Low T can cause decreased libido, fatigue, depression, muscle loss, and fertility issues. It's also just unsettling: "It's kind of frightening to think that there's something that is fundamentally changing our biology," Eisenberg said.

What to do? On a societal level, eliminating forever chemicals, obesity, and office jobs is a tall order. Individually, men can get tested, but treatment is murky. Supplements improve mood, bone density, red blood cells, and libido for those with low levels, but they paradoxically reduce sperm count and may not relieve symptoms.

Most experts agree that widespread screening, like Hegseth's military plan, is unnecessary. For the 90,000 female service members over 30, it's useless - testing women for low T is never recommended. For men without symptoms, the Endocrine Society advises against broad testing. Penn endocrinologist Peter Snyder noted it took screening over 50,000 men to find 800 participants for his "Testosterone Trials" - harder than getting into Penn med school. Broad screening risks false positives and overdiagnosis, leading to overtreatment. And while supplements would be optional, service members might feel pressured.

Maybe low testosterone isn't a disease but a marker of modernity, alongside eyestrain and belly paunch. The decline could be a bellwether that contemporary life is fundamentally changing us in ways we're only beginning to grasp.