Testosterone levels among men have declined significantly over the past half-century, an international group of researchers has determined after analyzing data on more than 100,000 men from seven countries. Testosterone has long been seen as a symbol of male health, physical strength, sexuality — in short, of “masculinity.” There are several reasons for the decline, but the main one is an obesity epidemic leading to related metabolic disorders. Among other factors, cientists cite changes in lifestyle, chronic stress, and environmental pollution. There is a hypothesis that the trend toward declining testosterone production could be reversed by the spread of drugs such as Ozempic, which promote weight loss. In fact, this theory is already gaining scientific support.
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What the new study actually showed
The British newspaper The Guardian, which published widely circulated news about a 54% global decline in men’s testosterone levels, described the trend as one of the most alarming findings in modern reproductive medicine. However, it is important to understand that the article was based not on a full scientific publication but on a presentation given at the annual congress of the European Society of Human Reproduction and Embryology (ESHRE). The researchers published only a brief description of the study — its main findings — without explaining the methodology, statistical analysis, or limitations of the research.
The authors examined data from studies on changes in men’s testosterone levels between 1972 and 2019. Of the more than 8,600 publications identified, only 12 studies met the selection criteria. These contained data on 102,334 men from seven countries — mostly, as the authors note, high-income ones. This means the findings may not fully reflect the situation in regions where comparable long-term data are still virtually nonexistent
The researchers analyzed three measures: total testosterone, free testosterone, and sex hormone-binding globulin. According to the meta-analysis, all three measures have declined significantly over the past 50 years. The authors also noted that after the year 2000, the rate of decline in total testosterone nearly doubled. However, the 54% figure cited by The Guardiandoes not appear in the study materials. It may have been mentioned during the presentation itself or included in the slides accompanying the talk (but this cannot currently be verified, as the slides are not publicly available).
It is also important to understand that such a meta-analysis can identify a statistical trend but cannot establish its causes. It shows that the measures are changing over time but does not answer the question of why. Moreover, the authors themselves note that the results may have been influenced by changes in the characteristics of the populations studied (such as the growing prevalence of obesity). As a result, they stress the need for further research
What you need to know about testosterone
In modern medicine, testosterone is regarded as one of the important markers of a man’s overall health. It plays a role in the development of the reproductive organs even before birth, and also plays a critical role in puberty, sperm production, libido, and erectile function. The hormone affects muscle mass, bone density, fat distribution, blood cell production, metabolism, and even brain function. Testosterone receptors have been found in virtually all tissues of the body
Modern medicine regards testosterone as a marker of a man’s overall health
But testosterone levels are not constant — they decline with age, and also follow circadian rhythms. Testosterone concentrations are usually highest in the early morning and gradually decline throughout the day. Because of these variations, it is recommended that blood tests be taken in the morning, and if the result is borderline or unexpectedly low, that the test be repeated on another day
In addition to natural daily fluctuations, testosterone levels are affected by body weight, sleep quality, physical activity, chronic diseases, certain medications, alcohol consumption, and stress. In other words, the level of testosterone reflects the overall state of the body
However, even taking individual fluctuations in testosterone levels into account, a decline in the average level may indicate that real biological changes are occurring in the population. If such a trend does indeed exist, what exactly is driving it?
Why testosterone levels are declining
Today, most researchers view declining testosterone levels as the result of an interplay of aging, chronic diseases, lifestyle, and environmental factors. At the same time, the strength of the evidence for different causes varies considerably. Some factors are supported by large epidemiological studies, clinical observations, and mechanistic data, while others are backed only by isolated observations and experimental models
Metabolism
Scientists are most confident about the negative role played by excess weight. Adipose tissue, particularly visceral fat (the kind that accumulates around the internal organs), literally converts testosterone into estradiol, the most active of the estrogens (female sex hormones). The more of this fat there is, the faster estrogen levels rise — and in turn, they suppress signals from the brain that trigger testosterone production in the testes. Low testosterone makes it easier to accumulate the same visceral fat, and so the cycle closes.
Excess weight is the main factor behind declining testosterone levels
This process is reversible, as numerous studies have confirmed. One of the first major meta-analyses, published in 2013 by a group of scientists from the University of Florence in Italy, showed that a low-calorie diet can increase testosterone levels (as can bariatric surgery to reduce the size of the stomach). Obesity is perhaps the only factor that can be effectively addressed: lose the excess weight, and hormone levels return to normal
Type 2 diabetes also causes testosterone levels to decline and leads to hypogonadism — a condition in which the body does not produce enough of the hormone. Persistently high blood sugar and insulin resistance disrupt signaling in the brain and directly affect the cells that produce testosterone. At the same time, low testosterone levels, in turn, reduce the sensitivity of organ tissues to insulin, creating another vicious cycle
Metabolic syndrome works in a similar way — a dangerous “cocktail” of high blood pressure, disrupted cholesterol levels, and abdominal obesity (when excess weight accumulates around the abdomen, surrounding the internal organs with metabolically active visceral fat)
The authors of a large population-based study, the Study of Health in Pomerania (SHIP), conducted in northeastern Germany, identified a pattern: the more components of the syndrome (a sagging belly, high blood pressure, and hormonal imbalances) a man has, the more rapidly his testosterone levels decline, with the effect particularly pronounced in younger patients
The more factors that lower testosterone accumulate in a man, the faster his hormone levels decline
Almost all metabolic disorders are accompanied by so-called systemic chronic inflammation. In obesity and diabetes, fat cells and macrophages (cells of the immune system) continuously release “alarm signals” into the bloodstream — pro-inflammatory cytokines — which directly attack the body’s testosterone “factories.” Laboratory experiments using cultures of Leydig cells (which synthesize the hormone in the testes) have shown that the higher the concentration of cytokines, the more strongly testosterone synthesis is suppressed.
Chronic inflammation literally “switches off” key enzymes inside cells, blocking the production of the hormone. Many modern endocrinologists agree that inflammation is how the harmful effects of excess weight, impaired glucose metabolism, and even the natural aging are mediated (the latter is known in science as “inflammaging,” or inflammatory aging)
Lifestyle
Unlike obesity or diabetes, the effects of lifestyle on testosterone levels have not been studied as extensively. The concept itself is too broad to be measured as precisely as blood sugar levels. Taken together, the evidence suggests that chronic stress, insufficient sleep, alcohol abuse, certain medications, and excessive physical activity can indeed lower levels of male sex hormones
Sleep is the most extensively studied factor in this group. Men produce the most testosterone at night, during the deeper stages of sleep, so it is logical to assume that sleep deprivation would directly affect the hormone. Evidence supporting this hypothesis was provided by a 2011 study by researchers at the University of Chicago: ten healthy young men slept for five hours a night for a week instead of their usual eight, and by the end of the experiment, their daytime testosterone levels had fallen noticeably, with the participants themselves beginning to complain of low energy and reduced libido.
Dozens of observational studies involving much larger groups subsequently confirmed the same pattern — an analysis by the U.S. National Center for Health Statistics involving thousands of participants, for one. However, when the effects of obesity and associated diseases are removed from the calculations, the link between sleep and testosterone levels weakens considerably, suggesting that insufficient sleep most likely reinforces the metabolic mechanisms described above
The mechanism by which chronic stress affects testosterone has been well-studied at the experimental level: it triggers the production of cortisol, which suppresses the signal from the brain that is essential for initiating the entire chain of testosterone synthesis. The problem is that at the population level, it is extremely difficult to standardize the very concept of “stress” — after all, strenuous physical work, anxiety, depression, and chronic illnesses produce very different hormonal effects. As large systematic reviews show, when data from thousands of men are analyzed, subjectively perceived psychological stress is only weakly associated with testosterone levels, unlike in strictly controlled experimental models.
In the case of alcohol, hormone production is clearly dose-dependent. In cases of chronic alcohol abuse, ethanol and its metabolite acetaldehyde directly damage Leydig cells and suppress the production of the regulatory hormone that gives these cells the signal to synthesize testosterone. A marked decline in total and free testosterone is found specifically in men with chronic patterns of alcohol consumption
Moderate consumption, however, is a different story: most studies have found no consistent clinically significant effect. Some short-term experiments have even shown a temporary spike in testosterone in response to small amounts of alcohol, but these changes quickly disappeared and had no lasting consequences
As for medications, it is specific groups of potentially harmful drugs that disrupt hormonal balance. The main enemy of testosterone in this case is potent opioid painkillers. When taken over a long period, they literally “switch off” the mechanism in the brain that signals the body to produce the male hormone. There is even a separate term for this condition — opioid-induced androgen deficiency (a deficiency of male sex hormones). Statistically, this problem affects upwards of 80% of men who take high dosages of certain painkillers for an extended period. T
Diet and physical activity
Contrary to “superfood” advertising campaigns, there is no magic diet for men’s health — what matters to the body is overall balance and metabolic health, not specific foods. Both overeating and starvation are equally harmful to the hormonal system.
Too much food leads to obesity (which, as noted above, literally destroys testosterone). However, strict diets and a sharp calorie deficit signal to the body that it is in survival mode, causing it to conserve energy. In such cases, the first thing to be shut down is the reproductive function. Additionally, a deficiency of zinc, magnesium, or vitamin D can cause a slight drop in testosterone levels, but for men whose blood tests are normal, an extra dose of vitamins will do absolutely nothing
There is no diet specifically designed to maintain “men’s health”
Large-scale meta-analyses confirm that physical activity does cause a substantial but short-lived spike in testosterone levels in men. Long-distance runners, however, have been found to show the opposite trend: excessive cardio exercise lowers baseline testosterone levels. This phenomenon is explained by relative energy deficiency in sport (RED-S) — with frequent endurance training, the body experiences a calorie deficit and deliberately suppresses the reproductive system. Thus, maintaining a stable hormonal balance requires moderation. Moderate strength training and adequate calorie intake stimulate testosterone production, while chronic excessive cardio training has the opposite effect. And the long-term effects of exercise programs in older people vary considerably depending on the type and intensity of exercise.
Environmental factors
In recent years, there have been increasingly frequent claims that microplastic pollution and household chemicals are to blame for the global decline in testosterone levels. The leading proponent of this idea is Shanna Swan, a leading environmental epidemiologist at the Icahn School of Medicine in New York. She has raised the alarm about the issue on major media platforms — from the podcasts of Joe Rogan and Andrew Huberman to Netflix documentaries. In her book Count Down, Swan argues that plastic and household chemicals are threatening humanity with a reproductive apocalypse.
Proving this hypothesis is more difficult than establishing the effects of obesity or diabetes. The problem is methodological: in today’s world, it is impossible to create a “clean” control group. Microplastics and phthalates affect people even before birth and remain with them throughout their lives. In a “cocktail” of hundreds of substances, it is difficult to identify a specific “culprit” and prove its direct effect. Nevertheless, it is worth looking at the factors currently under active investigation.
First on the list of prime suspects is bisphenol A (BPA) — a basic component of rigid, transparent plastics, epoxy resins, and the inner lining of food cans. As a structural analogue of estrogen, the substance can fool the body by binding to hormone receptors. Large-scale laboratory tests demonstrate that in animals, BPA suppresses testosterone synthesis in the testes and interferes with the activity of brain structures that initiate this process. Cell experiments have also shown that the substance disrupts the biosynthesis of cholesterol — the primary raw material for producing the male hormone.
Bisphenol A (BPA) – a basic component of rigid transparent plastic – is considered one of the factors behind declining testosterone levels
However, when scientists test these findings in humans, they once again encounter contradictions. On the one hand, a large-scale meta-analysis of epidemiological studies in 2024 found an association in men between high concentrations of bisphenol and lower testosterone levels. On the other hand, the effects of BPA in real life appear to be quite modest. Another study, published in 2010, found that in adult men, higher urinary BPA levels were associated with only minimal fluctuations in sex hormones.
The next suspects are phthalates, which are used to make plastic soft and flexible. Their effects on fetal development are well documented. For example, Shanna Swan found that boys born to women with high concentrations of phthalates in their urine showed signs of reduced exposure to male sex hormones in the womb. This finding was later confirmed to varying degrees by large cohort studies in Sweden, Mexico and the United States, and Japan
The link between phthalates and testosterone in adult men has also been documented, but the effect is usually minimal, inconsistent, and highly dependent on the specific chemical compound. Data from the U.S. National Center for Health Statistics show that these substances significantly lower hormone levels only in men over 60. In younger people, the body can metabolize and eliminate these toxins quickly.
For adult men, the problem is different: according to a meta-analysis published in March 2026, phthalates impair sperm quality and motility. In other words, plastic-induced “chemical castration” is not a threat to adult men, but fertility problems certainly are
Chemicals significantly lower hormone levels only in men over 60
Next are the so-called forever chemicals (PFAS), which do not break down for decades, whether in the environment or in the body. Here, the findings are even more contradictory. Some studies have found a link between high concentrations of PFAS in the blood and low testosterone, while others have found no such association. Nevertheless, the link between “forever chemicals” and impaired sperm quality has been consistently confirmed
A large systematic review by a group of researchers from Michigan notes that the decline in sperm motility and concentration associated with PFAS is much more consistently observed than their effect on testosterone levels
Air pollution is also being considered as a factor in the global decline in testosterone. So far, this question has been addressed by only one large study, conducted by researchers in Beijing. From 2014 to 2019, they collected data on nearly 73,000 men aged 20 to 55 and compared their testosterone levels with concentrations of air pollutants both on the day of testing and during the preceding month
They found that the dirtier the air immediately before the measurement, the lower the testosterone level. A 10-microgram-per-cubic-meter increase in the concentration of fine particulate matter was associated with a roughly 1.6% drop in testosterone, while for larger particles, the decline was 1.1%. The figures are small, but the effect proved consistent and statistically significant across the enormous sample
Nevertheless, this study has significant limitations. First, the data do not show the effect that long-term exposure to a polluted environment may have on testosterone production. Second, it has not been established that particulate matter affects hormone levels directly rather than through some other factor. Third, pollution levels were assessed using data from urban monitoring stations rather than individual sensors — meaning the study does not account for who spent more time outdoors and who stayed indoors with an air purifier.
Finally, it is not entirely clear from the study data to what extent the participants’ lifestyle, stress, and sleep were taken into account — factors that may well accompany exposure to polluted air in a major city. In short, it is too early to speak of a sustained effect of air pollution on testosterone. In order to find a reliable answer, studies with individual exposure monitoring and long-term follow-up of the measured individuals are needed
It is too early to speak of a sustained effect of air pollution on testosterone
The last factor under discussion is climate change. Here, science is still limited to hypotheses and assumptions. Scientists have demonstrated that extreme heat is a proven threat to male fertility. However, studies of men engaged in strenuous work in conditions of constant overheating (such as foundry workers) show that although heat stress damages sperm, it has virtually no effect on testosterone levels. A global report published by The Lancet in 2025 clearly distinguishes established reproductive risks from the hypothetical effects of climate on the endocrine system.
An aging population
Could it be that there is no real decline in testosterone at all, and that it is all due to statistical artifacts – for example, the population is aging, more older men with comorbidities are included in samples, and the average level is falling as a result? Scientists have repeatedly tested this hypothesis
Virtually all major studies on the subject use statistics specifically adjusted for age: instead of comparing all men indiscriminately, they compare, say, 30-year-olds from a sample collected in the 1990s with 30-year-olds from a sample collected in the 2010s. Even with this methodology, the decline in testosterone persists
The Massachusetts Male Aging Study in the United States – one of the first and best-known studies on the subject – shows that a man who was 60 in 1989 had, on average, higher testosterone levels than a man who reached that age in the 2000s
A similar trend has been observed in a much more recent study by scientists at Tel Aviv University: after analyzing the results of tests performed on more than 100,000 men between 2006 and 2019, they found a sustained, statistically significant decline in testosterone that was independent of age. The trend persisted within each age group separately and could not be explained by the increase in obesity among the participants
What a decline in testosterone levels means
From a biological perspective, the consequences of declining testosterone extend far beyond what is usually associated with “male strength.” They include loss of muscle mass, an increase in body fat (which, as noted above, only exacerbates the problem), an increased risk of osteoporosis, metabolic disorders, and an overall decline in quality of life. In some cases, fertility is also affected
For the healthcare system, this translates into an additional burden on clinics. Demographic consequences, however, should be discussed with caution: there is simply no scientific evidence yet directly linking declining testosterone levels to falling birth rates at the population level. A man can have perfectly normal hormone levels and still experience reproductive problems for dozens of other reasons. Conversely, fertility is not necessarily affected in all men with low testosterone
Can the spread of weight-loss drugs reverse this trend?
Importantly from a scientific standpoint, obesity has been shown to be the factor that has the strongest effect on testosterone levels. Could widespread weight loss driven by the growing use of drugs such as Ozempic reverse the downward trend in this hormone? GLP-1 receptor agonists — semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) — slow gastric emptying and suppress appetite, causing patients to lose an average of 10–17% of their body weight
Data from the past two years have so far supported this hypothesis. A retrospective study based on a sample of 234 men, presented at the Endocrine Society’s annual meeting (ENDO) in San Francisco in 2025, found that after starting treatment with these drugs, both total and free testosterone levels increased in men with obesity
According to another study presented at the same event, over 18 months of treatment, the proportion of patients with normal testosterone levels in a group of 110 men with obesity or type 2 diabetes rose from 53% to 77% as they lost about 10% of their body weight. The researchers explain that weight loss increases levels of SHBG (sex hormone-binding globulin), which in turn raises total testosterone levels
Weight loss increases total testosterone levels
However, there is no shortage of evidence pointing in the opposite direction. Animal experiments show that GLP-1 agonists are not always capable of restoring testosterone levels lowered by a high-fat diet. Nevertheless, the widespread use of GLP-1 therapy in the coming years could become the largest natural experiment in the history of endocrinology
If the average testosterone level in the population begins to rise as obesity declines, this would provide one of the most compelling indirect confirmations of the metabolic hypothesis discussed above. If that does not happen, scientists will have to take a much closer look at other factors — the environment, modern lifestyles, and perhaps other potential causes that have yet to be identified
