Why Are Testosterone Levels Dropping Across Generations

Testosterone levels in men have been falling steadily for decades, and the decline is not simply a matter of men getting older. Multiple large studies, conducted across different countries and time periods, show that a man born in the 1960s typically had lower testosterone at any given age than a man born in the 1930s, and a man born in the 1980s is on track to have even less. The average drop works out to roughly one to two percent per year across diverse populations, a pace that outstrips the normal age-related decline any individual man experiences over his lifetime.¹ No single cause explains this trend. Instead, the evidence points to a tangle of factors, from expanding waistlines and chemical exposures to shifts in sleep, diet, and physical activity, all of which have changed dramatically over the same decades testosterone has been falling.

What the Population Studies Actually Show

The landmark study that put this issue on the map followed men in the Boston area across three measurement waves from the late 1980s to the early 2000s. It found a substantial age-independent decline in total testosterone that could not be explained by observable health and lifestyle changes, including shifts in smoking and body weight.² A similar pattern turned up in Danish population surveys, where younger birth cohorts had lower testosterone than older cohorts tested at the same ages.³ These weren’t small blips. The estimated population-level declines were larger in magnitude than the cross-sectional dip in testosterone typically seen as an individual man ages from, say, 40 to 60.

Not every dataset tells exactly the same story, though. A separate analysis of nationally representative U.S. data from the late 1980s through the early 2000s found little overall change in total testosterone or free testosterone across that window, though it did find declines in certain androgen metabolites and in sex hormone-binding globulin among younger white men.⁴ One reason studies can disagree is the way testosterone was measured. Commercial immunoassays, the workhorses of hospital labs, can carry significant biases compared to more precise methods. One comparison found that a widely used immunoassay systematically underestimated testosterone relative to the reference standard maintained by the CDC, especially at low concentrations.⁵ So part of the variation between studies may come down to which lab ran the blood samples and when. That said, the overall weight of evidence, drawn from multiple countries and measurement platforms, still supports a real generational decline.

Obesity Is the Biggest Single Factor, but It Is Not the Whole Story

If you had to pick one driver and one driver only, rising body weight would be the strongest candidate. Extra body fat, particularly visceral fat around the organs, actively converts testosterone into estrogen. Fat tissue also releases inflammatory signals that suppress testosterone production at its source. Epidemiological data consistently link low testosterone with obesity, insulin resistance, and unfavorable blood lipid profiles, and the relationship runs in both directions: low testosterone promotes fat gain, and fat gain further suppresses testosterone.⁶ Research on men with very low testosterone found they were roughly twice as insulin resistant as men with normal levels, driven by decreased responsiveness in the testes themselves.⁷

But obesity does not explain the full decline. A study that tracked individual men over roughly two decades found that weight gain accounted for about 16 percent of the variance in dropping testosterone. Even men who lost weight or stayed weight-stable over that period still saw their testosterone fall by about 19 percent on average.⁸ In the Danish data, adjusting for the concurrent rise in body mass index reduced the significance of the testosterone trend, but the shift in sex hormone-binding globulin remained even after that adjustment.³ Something else, or more likely several something-elses, is at work.

Endocrine-Disrupting Chemicals

Modern life marinates us in synthetic chemicals that our grandparents never encountered. Among the most studied are phthalates, a family of compounds found in flexible plastics, food packaging, personal care products, and dozens of other everyday items. These chemicals can interfere with Leydig cells in the testes, the cells responsible for making testosterone. In a large nationally representative U.S. sample, higher urinary levels of certain high-molecular-weight phthalates were associated with lower total, free, and bioavailable testosterone among men aged 60 and older. Each doubling of one common phthalate metabolite was linked to nearly an eight percent drop in total testosterone in that age group.⁹ A separate study confirmed that non-occupational phthalate exposure was related to reduced secretion of both testosterone and INSL3, another hormone produced by Leydig cells, raising concern given how pervasive these exposures are in the general population.¹⁰

Phthalates are far from the only chemicals implicated. Bisphenols, certain pesticides, flame retardants, and per- and polyfluoroalkyl substances (PFAS) all fall under the broad umbrella of endocrine-disrupting chemicals. The challenge is that people are typically exposed to a cocktail of these compounds simultaneously, making it hard to isolate the contribution of any single one. What researchers can say is that the total chemical burden has increased dramatically over the same decades testosterone has been falling, and the biological pathways these chemicals disrupt align with the hormonal shifts being observed.

What Happens Before You Are Even Born

Some of the damage may begin in the womb. Prenatal exposure to both chemical and non-chemical stressors can alter sex steroid pathways in the developing fetus. Animal research shows that prenatal stress may modify how anti-androgenic chemicals like phthalates affect reproductive development in infant boys.¹¹ Experimental work in mice has demonstrated that prenatal exposure to the synthetic glucocorticoid dexamethasone disrupted the expression of key sex-determining genes and lowered fetal testosterone concentrations, in parallel with reduced numbers of the steroidogenic cells that produce it.¹²

This line of research is still in its early stages for humans, but it raises the possibility that each successive generation arrives with a slightly different hormonal starting point, shaped by whatever chemical and psychological stressors the mother experienced during pregnancy. If the fetal environment programs the capacity of Leydig cells or alters how the hormonal axis is calibrated, the effects could persist into adulthood and potentially carry forward.

Sleep, Stress, and Sitting Still

Three of the most widespread lifestyle changes over recent decades, shorter sleep, higher chronic stress, and less physical activity, each independently drag testosterone down. A controlled trial found that total sleep deprivation reduced total testosterone, an effect that aligns with the broader population trend of sleeping less than previous generations did.¹³ Chronic psychological stress elevates cortisol, and cortisol and testosterone tend to move in opposite directions. In one clinical study of men with type 2 diabetes, higher cortisol levels tracked closely with lower testosterone.¹⁴

Sedentary behavior compounds the problem through several routes at once. Inactivity promotes visceral fat accumulation, which as noted earlier converts testosterone to estrogen and drives chronic inflammation that suppresses testosterone production. It also contributes to muscle loss, reduced blood flow, and disturbed sleep, all of which feed back into further hormonal decline.¹⁵ The modern economy has shifted dramatically away from physical labor over the past half-century, and screen-based leisure time has ballooned. It would be surprising if those shifts had no hormonal footprint.

Ultra-Processed Food as an Emerging Suspect

Diet has changed alongside everything else. A growing body of research links high consumption of ultra-processed foods to worse reproductive outcomes in men. Multiple cross-sectional studies have found that men eating more ultra-processed food tend to have lower sperm concentration, lower sperm motility, and lower serum testosterone. In one series of studies reviewed together, an unhealthy dietary pattern heavy in fried and industrially processed items was consistently associated with lower testosterone levels and a reduced testosterone-to-triglyceride ratio compared to healthier dietary patterns.¹⁶ The food additives used to enhance taste, texture, and shelf life in these products have themselves been identified as endocrine-disrupting chemicals, creating yet another exposure route beyond the packaging the food comes in.

Data from younger populations adds another layer. In a study of children and adolescents, higher intake of ultra-processed food showed associations with altered sex hormone-binding globulin levels and with increased free androgen index in girls, hinting that these dietary patterns may affect hormonal development early in life.¹⁷ Given that ultra-processed foods now make up over half of caloric intake in many Western countries, even a modest hormonal effect per serving could scale into a meaningful population-level shift over time.

The Smoking Paradox

Here is a counterintuitive wrinkle: smoking rates have plummeted over the same decades testosterone has fallen, and nicotine actually appears to raise testosterone, at least up to a point. An analysis of U.S. adults found a positive association between serum cotinine, a marker of nicotine exposure, and total testosterone after adjusting for confounding factors. The relationship held up to a cotinine level of about 487 ng/mL, above which testosterone started to decline.¹⁸ The original Boston study noted that the decline in testosterone could not be fully attributed to observed changes in smoking and other lifestyle factors, but the direction of the effect is suggestive.² In other words, the public-health victory of reducing smoking may have inadvertently removed a factor that was propping testosterone levels up, an ironic trade-off given how overwhelmingly beneficial smoking cessation is for longevity.

Opioids and Other Medications

The opioid crisis, which accelerated dramatically starting in the late 1990s, brought its own hormonal toll. A systematic review and meta-analysis found that men using opioids regularly had total testosterone levels roughly 165 ng/dL lower than non-users, a clinically meaningful suppression that held regardless of the specific opioid involved.¹⁹ Opioids suppress the hormonal signaling from the brain that tells the testes to produce testosterone, and the effect can persist as long as someone is taking the drug. With tens of millions of opioid prescriptions dispensed annually at the peak of the crisis, this is not a niche concern. Other commonly prescribed medications, including certain antidepressants, corticosteroids, and some blood pressure drugs, can also lower testosterone, though the effects tend to be smaller and more variable.

Health Consequences That Go Beyond Libido

When people hear “low testosterone,” they tend to think of sex drive and muscle mass. Those are real effects, but the downstream health implications are broader. Low testosterone is associated with increased cardiovascular risk, and multiple studies have identified it as an independent risk factor for both cardiovascular and all-cause mortality.²⁰ Research suggests that testosterone shortens a key cardiac electrical interval, improves blood sugar control, promotes blood vessel dilation, and has anti-obesity effects.²¹

That said, the relationship between testosterone and cardiovascular disease is not fully settled. Some reviewers note that while low testosterone tracks with metabolic syndrome and cardiovascular death in observational data, it remains possible that both low testosterone and cardiovascular disease are products of some other shared underlying factor, rather than one causing the other. Meta-analyses of testosterone replacement therapy have not consistently shown a significant reduction in cardiovascular events themselves.²² The population-level trend of declining testosterone is also associated with reduced fertility, mood disturbances, and diminished quality of life.²³

What You Can Actually Do About It

The generational trend is driven by population-wide forces that no individual fully controls, but a meaningful share of the decline is tied to modifiable factors. Weight loss is the single most impactful intervention supported by the evidence. Both moderate and significant reductions in body fat are associated with notable increases in serum testosterone. Dietary approaches, particularly lower-carbohydrate and Mediterranean-style diets, have been linked to improved testosterone production in men carrying extra weight. Resistance training helps by reducing fat mass and directly stimulating hormonal output. For severely obese men, bariatric surgery has emerged as one of the most effective methods for raising testosterone, with improvements that hold over time.²⁴

Beyond body composition, improving sleep duration and quality, reducing chronic stress, cutting back on ultra-processed food, and minimizing exposure to known endocrine disruptors (choosing glass or stainless steel over soft plastic for food storage, checking personal care products for phthalates) are all steps that align with the mechanistic evidence. None of these is a silver bullet, and the in utero and early-life exposures that may have programmed some of the decline are by definition not reversible after the fact. But stacking several of these lifestyle changes can produce measurable hormonal improvements.

The Parallel Decline in Sperm Counts

Testosterone is not declining in isolation. Global sperm concentration dropped by over 50 percent between 1973 and 2018, and the rate of decline has been accelerating, from about one percent per year before 2000 to nearly three percent per year afterward.¹ The overlap in suspected causes, endocrine disruptors, obesity, poor diet, sedentary behavior, suggests these are not independent trends but reflections of the same broader assault on male reproductive biology. Evolutionary biologists have long noted that testosterone mediates trade-offs between reproduction and long-term survival, allocating resources toward mating effort at the cost of immune function and tissue maintenance.²⁵ In an environment where energetic resources are abundant but chemical stressors are novel, the body’s calibration of that trade-off may be shifting in ways evolution never had to contend with before. Whether that shift is simply a marker of a changed environment or represents a genuine threat to population health is one of the more pressing questions in reproductive endocrinology today.