The clinical syndrome at the heart of the debate is defined by the coexistence of characteristic symptoms with persistently low serum testosterone concentrations. That dual requirement matters, because testosterone levels alone tell an incomplete story. The condition exerts wide-ranging effects across the male body, influencing sexual function, metabolic health, bone integrity, mood, haematopoiesis and overall quality of life. The authors classify hypogonadism into three broad categories: primary hypogonadism, arising from testicular failure; secondary hypogonadism, driven by dysfunction of the hypothalamic–pituitary axis; and functional hypogonadism, a form commonly associated with ageing, obesity and chronic systemic disease. The functional category has attracted growing attention because it blurs the line between endocrine disease and the physiological consequences of modern lifestyles, and because it may be partially reversible when the underlying drivers are addressed.

The mechanistic interplay between adiposity and testosterone is particularly striking. Adipose tissue expresses aromatase, the enzyme that converts androgens into oestrogens, so expanding fat mass both consumes testosterone and suppresses the hypothalamic–pituitary–gonadal axis through feedback and inflammatory adipocytokine signalling. This hypogonadal–obesity–adipocytokine hypothesis, illustrated in the review, describes a self-reinforcing cycle: low testosterone promotes visceral fat accumulation and insulin resistance, which in turn further suppress testosterone production. Recent work cited in the review has documented altered expression of aromatase and oestrogen receptors in adipose tissue from men with obesity and type 2 diabetes, providing a molecular substrate for the clinical observations. Breaking this cycle, whether through weight loss, pharmacotherapy or testosterone replacement itself, is therefore a central therapeutic goal.

Diagnosis remains the discipline’s most contested territory, and the review is emphatic about rigour. Confirmation requires both clinical features and biochemical evidence, typically obtained through morning serum testosterone measurements, because testosterone follows a diurnal rhythm that flattens with age and is blunted by poor sleep and illness. When values fall into a borderline zone, or when symptoms and total testosterone concentrations appear discordant, measurement of sex hormone-binding globulin and calculated free testosterone can provide additional clarity, since a substantial fraction of circulating testosterone is bound and biologically inactive. The authors highlight recent joint position statements from the Society for Endocrinology and the Association for Clinical Biochemistry and Laboratory Medicine aimed at standardizing biochemical confirmation, an attempt to reduce the diagnostic variability that has plagued the field. Symptom questionnaires such as the Aging Males’ Symptoms scale and the quantitative ADAM instrument can support, but never replace, laboratory confirmation.

Once the diagnosis is secure, the evidence for treatment is substantial. Meta-analyses of randomized trials report consistent improvements in sexual desire and erectile function, with testosterone therapy also enhancing the response to phosphodiesterase 5 inhibitors in men who previously failed to respond. The large TRAVERSE trial programme has added high-quality data on mood, showing improvement in depressive syndromes among hypogonadal men, while earlier trials demonstrated benefits in energy and health-related quality of life. Haematological effects are equally well documented: testosterone stimulates erythropoiesis, and randomized studies have shown that replacement therapy corrects anaemia in hypogonadal men, a finding with potential relevance for older men whose fatigue and functional decline are partly attributable to low red cell mass.

Metabolic and skeletal outcomes form a second pillar of benefit. Trials in men with type 2 diabetes and metabolic syndrome, including the TIMES2 study and the T4DM trial, indicate that testosterone replacement improves insulin resistance, glycaemic control and body composition, reducing fat mass while increasing lean mass. Registry data suggest that long-term therapy can even be associated with remission of type 2 diabetes in some hypogonadal men. On bone, testosterone is aromatized to oestradiol in skeletal tissue, and both sex steroids contribute to bone maintenance. Randomized trials have shown increases in bone mineral density and improvements in volumetric bone strength, and a 2024 analysis in the New England Journal of Medicine reported that testosterone treatment reduced fracture risk in men with hypogonadism, converting a long-standing surrogate outcome into a hard clinical endpoint.

Safety has been the field’s defining controversy. The historical fear that testosterone fuels prostate cancer stemmed from the observation, dating to Huggins and Hodges in 1941, that androgen deprivation shrinks metastatic disease. The modern saturation model proposes instead that androgen-dependent growth plateaus at low concentrations, so raising testosterone from deficient to normal levels has limited proliferative effect. Contemporary data reviewed by the authors, including meta-analyses of prostate cancer incidence in treated men and studies of therapy in prostate cancer survivors after definitive local treatment, do not demonstrate increased oncological risk when monitoring is appropriate. Cardiovascular safety has followed a similar arc from alarm to reassurance: early observational studies suggesting excess myocardial infarction were followed by the TRAVERSE trial, published in 2023, which found that testosterone replacement did not increase major adverse cardiovascular events in middle-aged and older men, and by subsequent European expert panel position statements concluding that appropriately monitored therapy is cardiovascularly safe.

Not all risks can be dismissed, however, and the review is candid about the caveats. Testosterone therapy suppresses spermatogenesis through inhibition of gonadotropin secretion, making it inappropriate for men who wish to preserve fertility; alternatives such as selective oestrogen receptor modulators, aromatase inhibitors, human chorionic gonadotropin and, in trials of male obesity-related hypogonadism, the aromatase inhibitor leflutrozole can raise testosterone while maintaining or restoring sperm production. Erythrocytosis remains the most common laboratory adverse effect requiring dose adjustment, and testosterone therapy can worsen obstructive sleep apnoea, which should be assessed and treated before and during treatment. The authors also flag a practical laboratory pitfall: contamination of the venipuncture site with topical testosterone gel can produce falsely elevated readings, a reminder that even the diagnostic pathway demands attention to detail.

The therapeutic arsenal has expanded considerably. Transdermal gels and solutions remain the most widely used formulations, offering physiological absorption but requiring daily application and posing a theoretical risk of transfer to partners and children. Newer oral testosterone undecanoate formulations, absorbed via the lymphatic system when taken with food, avoid the hepatotoxicity that doomed earlier oral preparations and have shown efficacy across body mass index ranges in phase III trials. Long-acting intramuscular testosterone undecanoate injections provide stable levels for ten to fourteen weeks, while subcutaneous enanthate auto-injectors and subdermal pellets serve patients who prefer less frequent administration. Intranasal gel offers rapid achievement of steady-state levels and, notably, has been shown in trials to preserve semen parameters better than other routes, an option for younger men with fertility concerns. Patient preference, adherence data and pharmacokinetic profiles all inform the choice, and the review stresses that individualized selection, careful counselling and structured monitoring of testosterone levels, haematocrit and prostate-specific antigen are essential to optimize outcomes.

The broader significance of this update lies in its recalibration of a polarized debate. The evidence now supports a middle path: testosterone deficiency is a real and treatable syndrome with demonstrable benefits across sexual, metabolic, skeletal, haematological and psychological domains, but it is neither a panacea for ageing nor a condition to be diagnosed from a single afternoon blood test. Regulatory bodies, including the European Medicines Agency and the US Food and Drug Administration, have moved toward positions consistent with the trial evidence, though the FDA continues to require labelling about possible cardiovascular risk in age-related use. For the millions of men worldwide whose symptoms, metabolic disease and bone fragility intersect with low testosterone, the message from this authoritative synthesis is measured but clear: with rigorous diagnosis, appropriate patient selection and disciplined monitoring, testosterone replacement therapy has earned its place in modern endocrine practice.

Subject of Research: Diagnosis, clinical benefits and safety of testosterone replacement therapy in male hypogonadism

Article Title: Update on testosterone deficiency and therapeutic options for testosterone replacement therapy

Article References: Thompson, T., Mubarak, M., Jones, T. H., Pearce, I., & Modgil, V. (2026). Update on testosterone deficiency and therapeutic options for testosterone replacement therapy. Nature Reviews Urology. https://doi.org/10.1038/s41585-026-01190-3

Image Credits: AI Generated

DOI: 10.1038/s41585-026-01190-3

Keywords: testosterone deficiency, male hypogonadism, testosterone replacement therapy, hypothalamic-pituitary-gonadal axis, obesity, type 2 diabetes, bone mineral density, cardiovascular safety, prostate cancer, TRAVERSE trial, free testosterone, hypogonadism diagnosis

Testosterone is central to male reproductive biology, but its effects extend throughout the body. The hormone contributes to sperm production, sexual function, muscle maintenance, bone strength, red blood cell formation, mood and energy regulation. Levels vary substantially between individuals and fluctuate with age, sleep, illness, stress, body composition, medications and the time of day. That biological variability makes testosterone testing deceptively difficult: a single low result does not automatically mean that a man has a medical disorder requiring treatment.

The authors’ focus on military personnel is significant because service members operate in environments where physical performance, mental resilience and long-term health are closely monitored. Military populations also share structured medical systems, standardized occupational demands and detailed health records, creating conditions in which screening strategies could be evaluated more rigorously than in fragmented healthcare settings. If designed carefully, routine testing could reveal how testosterone levels relate to symptoms, fitness, recovery, metabolic health and deployment-related stress without assuming that every abnormal result represents disease.

A major technical challenge is deciding what constitutes a genuinely low testosterone level. Testosterone follows a circadian rhythm, generally reaching its highest concentrations in the morning and declining later in the day. Concentrations can also fall temporarily during acute infection, severe calorie restriction, sleep deprivation or intense physical stress. For that reason, clinical assessment typically depends on a combination of symptoms and consistently low measurements, ideally obtained through properly timed morning blood samples and confirmed with repeat testing. Laboratory methods also matter, because different assays can produce meaningfully different results.

The hormone circulating in blood exists in several forms. Some testosterone is tightly bound to proteins, while another fraction is loosely bound or remains unbound and is considered more biologically available. Conditions that alter sex hormone-binding globulin, including obesity, thyroid disorders, liver disease and aging, can change total testosterone without producing the same change in active hormone. A technically sound screening program would therefore need to account for these variables and use validated laboratory techniques rather than relying on a single universal cutoff.

The prospect of routine screening is likely to attract attention because testosterone therapy has become increasingly visible in popular culture. Clinics and online companies frequently market testosterone as a solution for fatigue, reduced libido, weight gain or declining athletic performance. Yet these symptoms are nonspecific and may arise from depression, sleep apnea, medication effects, overtraining, diabetes, obesity or chronic disease. Expanding testing without clinical safeguards could encourage unnecessary treatment, expose healthy men to avoidable risks and reinforce the misleading idea that testosterone is a general-purpose performance enhancer.

Testosterone replacement can be appropriate for men with confirmed hormone deficiency and compatible clinical symptoms, but it is not risk-free. Treatment can suppress the body’s own testosterone production and reduce sperm production, making it unsuitable for men seeking fertility in the near term. It can also increase red blood cell production, requiring monitoring for erythrocytosis, and may worsen untreated sleep apnea or complicate the evaluation of prostate health. Cardiovascular safety remains an area of active clinical discussion, which further underscores the importance of individualized assessment rather than automatic treatment after a low laboratory result.

For military organizations, the consequences of poorly designed screening could extend beyond individual medical decisions. A test result might affect deployment eligibility, career progression, insurance, privacy or perceptions of physical capability. Any program would therefore need strict rules governing informed consent, confidentiality, data access and the separation of health protection from disciplinary or employment decisions. Service members should not be pressured into testing or treatment merely because a hormone measurement is available, and abnormal results should trigger careful clinical evaluation rather than administrative labeling.

The authors’ argument is ultimately less about testing everyone than about building a reliable evidence base for men’s health. Military health systems could help researchers study how testosterone measurements perform across different ages, occupations, training loads and environmental conditions. Long-term data might clarify which symptoms and biological markers best predict clinically meaningful deficiency, which men benefit from treatment and whether screening improves outcomes compared with symptom-led testing. Such research could also expose important gaps, including how testosterone-related care should be adapted for diverse ethnic groups, transgender and gender-diverse personnel, and men with chronic illness.

As testosterone moves from a niche endocrine concern into a viral topic in wellness culture, the call for evidence-based implementation is timely. Routine screening could improve recognition of genuine hormone disorders, but only if it is paired with accurate assays, repeat testing, symptom assessment, fertility counseling and protection against overtreatment. The military may offer a uniquely organized setting to test that model, yet the broader lesson applies far beyond the barracks: testosterone is a clinically meaningful hormone, not a standalone scorecard for health, masculinity or performance.

Subject of Research: Routine testosterone screening in military personnel and its potential role in evidence-based men’s health.

Article Title: Routine testosterone screening in military personnel: an opportunity for evidence-based implementation in men’s health.

Article References: Mubarak, M., Modgil, V. Routine testosterone screening in military personnel: an opportunity for evidence-based implementation in men’s health. Nature Reviews Urology (2026). https://doi.org/10.1038/s41585-026-01181-4

Image Credits: AI Generated

DOI: 10.1038/s41585-026-01181-4

Keywords: testosterone screening, military health, men’s health, hypogonadism, testosterone deficiency, hormone testing, endocrinology, evidence-based medicine, testosterone therapy, reproductive health