Testosterone Deficiency: Why More Men Are Affected Than Ever

Testosterone Deficiency: Why More Men Are Affected Than Ever

Testosterone deficiency has become increasingly recognised as a common health issue, with evidence that more men are affected today than in previous generations, and that this sits within a wider decline in male reproductive health.

From Discovery to Medical Treatment

Testosterone was first isolated in 1935, when Ernst Laqueur obtained crystalline testosterone from bull testes and, independently, Adolf Butenandt and Leopold Ruzicka achieved full chemical synthesis of the hormone. These breakthroughs meant testosterone could be produced reliably and in sufficient quantities for therapeutic use rather than just for experimental work. Early oral preparations were limited by rapid hepatic inactivation, prompting the development of injectable esters and later transdermal and longer-acting depot formulations that better mimic physiological levels. Over the following decades, formulations were refined to provide more stable serum concentrations and improved tolerability, forming the basis of modern testosterone replacement therapy (TRT).

How Testosterone Entered Clinical Practice

Clinically, testosterone was initially used for classic hypogonadism due to testicular failure or pituitary disease, where benefits for sexual function, muscle mass and bone health were obvious. As understanding grew, age-related (late-onset) hypogonadism was recognised as a syndrome of low serum testosterone combined with symptoms such as reduced libido, erectile dysfunction, depressed mood, fatigue and loss of vitality. Large cohort studies like the Baltimore Longitudinal Study of Aging showed that total testosterone falls steadily with age, with hypogonadism affecting about 20% of men in their 60s, 30% in their 70s and roughly half of those in their 80s, using biochemical cut-offs alone. Modern guidelines therefore emphasise both symptoms and consistently low levels before initiating TRT, with ongoing monitoring for efficacy and safety.

How Common Testosterone Deficiency Is Now vs. the Past

Defining testosterone deficiency is challenging because different studies use different thresholds (often 200-400 ng/dL), but global estimates now suggest 10-40% of adult men may have biochemical or symptomatic deficiency depending on age and criteria used. One major US population-based analysis estimated symptomatic androgen deficiency at 5.6% of men aged 30-79, rising sharply with age, and projected that the burden would increase by 38% between 2000 and 2025 due to population ageing alone.

Longitudinal data indicate that average testosterone levels have been declining across birth cohorts, not just with ageing; for example, analyses of men tested between the 1980s and early 2000s showed lower testosterone at a given age in more recent cohorts, suggesting environmental and lifestyle factors beyond normal ageing. Cross-sectional surveys also show a large gap between men with high symptom scores suggestive of deficiency and those formally diagnosed, implying that a substantial proportion of affected men remain untreated.

Why Testosterone Deficiency May Be Increasing

Several interacting trends are thought to underlie the apparent rise in testosterone deficiency and related symptoms.

Endocrine Disrupting Chemicals (EDCs)

A growing body of epidemiological and experimental work links ubiquitous chemicals such as phthalates, bisphenol A, certain pesticides and other industrial pollutants to reduced testosterone synthesis and impaired testicular function. Human data from large surveys like NHANES show an inverse relationship between urinary phthalate metabolites and circulating testosterone in men, with some exposures associated with 10-30% lower testosterone levels. Mechanistically, EDCs can interfere with Leydig cell steroidogenesis, disrupt the hypothalamic-pituitary-gonadal axis, increase oxidative stress and induce epigenetic changes affecting reproductive tissues.

Pesticides and Environmental Pollutants

Animal and human studies indicate that chronic low-dose exposure to certain herbicides and pesticides, including glyphosate-based formulations, can damage testicular structure, lower serum testosterone and reduce sperm counts. Reviews conclude that persistent pollutants contribute to reduced sperm concentration, motility and DNA integrity, alongside hormonal disruption, even at exposure levels found in the general population.

Calorie-Dense, Nutrient-Poor Diets and Obesity

Rising rates of obesity and metabolic syndrome are strongly associated with lower total and free testosterone, through mechanisms including increased aromatisation of androgens to oestrogens in adipose tissue, insulin resistance and chronic low-grade inflammation. Observational studies consistently show that higher BMI and central adiposity correlate with reduced testosterone, while weight loss and improved diet can partially reverse this.

Sedentary Lifestyles and Chronic Stress

Physical inactivity, poor sleep and chronic psychosocial stress are all linked to lower testosterone and poorer reproductive parameters. Regular resistance and aerobic exercise, on the other hand, can improve testosterone levels and mitigate some age-related decline, particularly when combined with weight reduction. Modern work patterns, screen time and reduced physical labour likely contribute to the background shift in hormonal milieu.

Collectively, these factors mean contemporary men are exposed to a very different environment than their counterparts 50 years ago, with multiple simultaneous pressures on androgen production and reproductive health.

Declining Male Fertility and What It Means

Parallel to changes in testosterone, multiple meta-analyses have documented a substantial, ongoing decline in sperm counts and other semen parameters over the last half-century. A landmark systematic review and meta-analysis reported that sperm concentration and total sperm count in men from Western countries dropped by more than 50% between the 1970s and early 2010s, with more recent updates showing that the decline is global and appears to be continuing into the 21st century at an accelerated rate.

Reviews of male fertility consistently implicate endocrine disrupting chemicals, air pollution, smoking, poor diet, obesity, heat exposure and lifestyle factors in reduced sperm concentration, motility, morphology and DNA integrity. Because adequate testosterone is essential for spermatogenesis, disturbances in androgen signalling and direct testicular toxicity from pollutants likely work together to drive the fertility decline.

The implications of sustained reductions in testosterone and male fertility are wide-ranging. At an individual level, men may experience sexual dysfunction, reduced wellbeing, sarcopenia, osteoporosis risk and metabolic complications, while couples face increasing difficulty conceiving without assisted reproduction. At a population level, continued downward trends in sperm count and reproductive capacity could further depress birth rates in already low-fertility societies, strain fertility services and raise complex ethical and social questions about environmental stewardship, intergenerational health and the medicalisation of reproduction.

Addressing these trends will require not only better diagnosis and treatment of testosterone deficiency, but also upstream action on environmental exposures, urban design, food systems and broader determinants of male health.