Understanding Testosterone Levels in Men
Understanding Testosterone Levels in Men
Key Takeaways
- Normal testosterone levels in adult men range from 300-1,000 ng/dL, though optimal levels vary by age and individual health factors.
- The American Urological Association defines low testosterone (hypogonadism) as levels below 300 ng/dL combined with clinical symptoms.
- Testosterone naturally declines approximately 1-2% per year after age 30, though individual variation is significant.
- The landmark TRAVERSE trial (2023) demonstrated cardiovascular safety of testosterone replacement therapy in properly diagnosed men.
- Diagnosis requires both laboratory confirmation AND clinical symptoms—numbers alone don't tell the whole story.
Introduction: Why Testosterone Matters
Testosterone is far more than "just a hormone." As the primary androgen in the male body, it orchestrates a complex symphony of physiological processes that influence virtually every aspect of men's health—from muscle strength and bone density to cognitive function, mood regulation, and metabolic health.
Yet despite its critical importance, testosterone deficiency remains both underdiagnosed and overtreated. According to research published in the Journal of Clinical Endocrinology & Metabolism, approximately 35% of men over 45 and 30-50% of men with obesity or type 2 diabetes experience hypogonadism—many without knowing it.
At Arsenal Men's Health, we believe that understanding your testosterone levels empowers you to make informed decisions about your health. This comprehensive guide provides the clinical depth, evidence-based insights, and practical guidance you need—whether you're investigating symptoms, considering treatment, or simply optimizing your health trajectory.
What Is Testosterone? The Science Behind the Hormone
Testosterone is a steroid hormone belonging to the androgen class, primarily produced in the Leydig cells of the testes (approximately 95%), with smaller amounts synthesized in the adrenal glands. In women, testosterone is produced in the ovaries and adrenal glands in much smaller quantities.
The Hypothalamic-Pituitary-Gonadal (HPG) Axis
Testosterone production is regulated through a sophisticated feedback system known as the hypothalamic-pituitary-gonadal (HPG) axis:
- Hypothalamus: Releases gonadotropin-releasing hormone (GnRH) in pulsatile patterns
- Pituitary Gland: Responds to GnRH by secreting luteinizing hormone (LH) and follicle-stimulating hormone (FSH)
- Testes: LH stimulates Leydig cells to produce testosterone; FSH supports spermatogenesis
- Feedback Loop: Circulating testosterone inhibits further GnRH and LH release, maintaining homeostasis
This feedback mechanism is clinically important because exogenous testosterone therapy can suppress the HPG axis, potentially affecting fertility—a key consideration we discuss thoroughly with every patient at Arsenal Men's Health.
Types of Testosterone in Your Blood
When measuring testosterone, it's essential to understand that it circulates in three forms:
- Free Testosterone (1-3%): Unbound and biologically active, readily available for tissue uptake
- Albumin-Bound Testosterone (~40%): Loosely bound, can dissociate and become active ("bioavailable" when combined with free testosterone)
- SHBG-Bound Testosterone (~55-60%): Tightly bound to sex hormone-binding globulin, essentially inactive
Total testosterone measures all three forms combined, while free testosterone isolates only the biologically active portion. In cases where total testosterone is borderline or when conditions affecting SHBG are present (obesity, liver disease, thyroid disorders), measuring free testosterone provides additional clinical clarity.
Testosterone's Role in Men's Health
Testosterone influences virtually every organ system in the male body. Understanding these effects helps contextualize why low testosterone produces such wide-ranging symptoms:
Sexual Function & Libido
Testosterone is essential for maintaining sexual desire and supporting erectile function. Research published in the Journal of Sexual Medicine demonstrates that testosterone modulates nitric oxide synthase activity in penile tissue, directly influencing erectile response. The hormone also activates neural pathways in the brain that regulate libido and sexual motivation.
Muscle Mass & Strength
Testosterone promotes protein synthesis and inhibits protein catabolism, creating an anabolic environment for muscle growth. The Testosterone Trials (TTrials) demonstrated that testosterone therapy increases fat-free mass and muscle strength in hypogonadal men, with effects becoming clinically significant within 3-6 months of treatment.
Bone Health & Density
Testosterone maintains bone mineral density through multiple mechanisms: direct activation of osteoblasts (bone-building cells), suppression of osteoclasts (bone-resorbing cells), and conversion to estradiol, which has additional bone-protective effects. The TTrials Bone Trial showed that testosterone therapy increases volumetric bone mineral density and estimated bone strength in the spine and hip.
Metabolic Function
Testosterone influences body composition by reducing visceral adipose tissue and improving insulin sensitivity. Research presented at ENDO 2024 demonstrated that adequate testosterone levels appear protective against type 2 diabetes development in men under 65 with overweight or obesity—a finding with significant public health implications.
Cognitive Function & Mood
Testosterone receptors are widely distributed throughout the brain, including areas involved in memory, mood regulation, and executive function. While the TTrials found no improvement in cognitive function with testosterone therapy, data from the TRAVERSE trial showed improvements in depressive symptoms in hypogonadal men receiving treatment.
Cardiovascular & Hematologic Function
Testosterone stimulates erythropoiesis (red blood cell production), which explains both its therapeutic benefit in anemia and the need for hematocrit monitoring during therapy. The relationship between testosterone and cardiovascular health has been extensively studied, with the TRAVERSE trial providing reassuring safety data that we discuss in detail below.
What Are Normal Testosterone Levels?
Defining "normal" testosterone is more nuanced than simply citing a reference range. The Endocrine Society Clinical Practice Guideline recommends using assays harmonized to the CDC Hormone Standardization Program, which establishes a lower limit of normal at approximately 264 ng/dL (9.2 nmol/L) in healthy, nonobese young men.
However, the American Urological Association and most clinical laboratories use 300 ng/dL as the threshold for defining low testosterone, with the normal range typically spanning 300-1,000 ng/dL.
Age-Specific Reference Ranges: Emerging Evidence
A groundbreaking 2022 study published in the Journal of Urology by Dupree and colleagues analyzed testosterone levels in 1,486 men aged 20-44. Their findings challenge the one-size-fits-all 300 ng/dL cutoff:
| Age Group | Recommended Low-T Threshold | Clinical Significance |
|---|---|---|
| 20-24 years | 409 ng/dL | Peak testosterone period |
| 25-29 years | 388 ng/dL | Early decline may begin |
| 30-34 years | 369 ng/dL | Gradual decline typical |
| 35-39 years | 360 ng/dL | Symptoms may emerge |
| 40-44 years | 350 ng/dL | Standard cutoff appropriate |
| 45+ years | 300 ng/dL | AUA/Endocrine Society standard |
Table 1: Age-Specific Testosterone Thresholds (Adapted from Dupree et al., J Urol 2022)
This research suggests that using a uniform 300 ng/dL cutoff may miss testosterone deficiency in younger men who should have higher levels. At Arsenal Men's Health, we interpret results within the context of your age, symptoms, and overall health profile.
Why Do Testosterone Levels Decline?
Primary Hypogonadism
Primary hypogonadism (also called hypergonadotropic hypogonadism) occurs when the testes cannot produce adequate testosterone despite receiving proper signals from the brain. The pituitary responds by increasing LH and FSH production—a distinguishing laboratory finding.
Causes include:
- Klinefelter syndrome (47,XXY karyotype)
- Testicular trauma or torsion
- Orchitis (including mumps orchitis)
- Chemotherapy or radiation therapy
- Varicocele
Secondary Hypogonadism
Secondary hypogonadism (hypogonadotropic hypogonadism) results from inadequate stimulation of the testes due to hypothalamic or pituitary dysfunction. LH and FSH levels are low or inappropriately normal.
Causes include:
- Pituitary tumors or disease
- Kallmann syndrome
- Obesity (aromatization of testosterone to estrogen in adipose tissue)
- Chronic opioid use
- Anabolic steroid abuse (causes profound HPG axis suppression)
- Hyperprolactinemia
Age-Related Decline
Testosterone naturally declines with age at a rate of approximately 1-2% per year beginning in the 30s or 40s. This process, sometimes called "andropause" or "late-onset hypogonadism," differs from the abrupt hormonal changes of female menopause.
Concerning research published in the International Journal of Impotence Research (2025) demonstrates that testosterone levels in younger men today are lower than in previous generations—a trend potentially attributable to environmental factors, increased obesity rates, and lifestyle changes.
Symptoms and Signs of Low Testosterone
Low testosterone manifests across multiple domains, with symptoms that can significantly impact quality of life. The Endocrine Society emphasizes that diagnosis requires both laboratory confirmation AND clinical symptoms—a principle we strictly adhere to at Arsenal Men's Health.
Sexual Symptoms
- Decreased libido (often the first and most sensitive symptom)
- Erectile dysfunction or reduced erectile quality
- Loss of morning erections
- Reduced ejaculate volume
Physical Symptoms
- Decreased muscle mass and strength
- Increased body fat, particularly visceral (abdominal) fat
- Fatigue and reduced stamina
- Decreased bone mineral density
- Reduced body and facial hair growth
- Hot flashes (in severe deficiency)
Psychological Symptoms
- Depressed mood and irritability
- Decreased motivation and drive
- Difficulty concentrating ("brain fog")
- Sleep disturbances
How Is Testosterone Tested?
Accurate diagnosis of testosterone deficiency requires proper testing methodology. The Endocrine Society Clinical Practice Guideline provides clear recommendations:
Timing and Methodology
- Morning Testing (7-10 AM): Testosterone follows a circadian rhythm, peaking in early morning. Testing later in the day can yield falsely low results.
- Fasting State: Fasting morning samples provide the most accurate results.
- Confirmation Testing: Diagnosis requires at least two separate low readings—single measurements can be affected by acute illness, stress, or laboratory variability.
- Reliable Assay: We use CLIA-certified laboratories with assays harmonized to CDC standards for optimal accuracy.
Additional Testing Considerations
When total testosterone is borderline or when clinical suspicion is high despite normal total testosterone, additional testing may include:
- Free Testosterone: Particularly valuable when SHBG-altering conditions are present
- LH and FSH: Differentiates primary from secondary hypogonadism
- Prolactin: Elevated levels may indicate pituitary pathology
- Complete Blood Count: Baseline assessment before therapy
- Metabolic Panel: Assesses kidney and liver function
- PSA: Baseline prostate assessment in appropriate age groups
The TRAVERSE Trial: Landmark Evidence on Safety
The TRAVERSE trial (Testosterone Replacement therapy for Assessment of long-term Vascular Events and efficacy ResponSE in hypogonadal men), published in the New England Journal of Medicine in 2023, represents the most definitive evidence to date on cardiovascular safety of testosterone therapy.
Study Design
- 5,246 men aged 45-80 years enrolled
- All participants had preexisting or high risk of cardiovascular disease
- All had confirmed hypogonadism (two fasting testosterone levels <300 ng/dL)
- Randomized to transdermal testosterone gel vs. placebo
- Mean follow-up of 22 months
Key Findings
Primary Cardiovascular Endpoint: Major adverse cardiac events (cardiovascular death, non-fatal myocardial infarction, or non-fatal stroke) occurred in 7.0% of testosterone-treated patients vs. 7.3% of placebo patients—demonstrating non-inferiority and supporting cardiovascular safety.
As stated by the European Expert Panel for Testosterone Research (PaTeR) in their 2025 position statement: consistent with other meta-analyses and guidelines, the TRAVERSE trial found no significant increase in major adverse cardiac events associated with testosterone therapy when used appropriately.
Additional TRAVERSE Sub-Studies
- Fracture Risk: Testosterone treatment significantly reduced fracture risk in hypogonadal men
- Depression: Improvements in depressive symptoms observed in the testosterone group
- Sexual Function: Significant improvements in sexual function and hypogonadal symptoms
- Diabetes Prevention: 22.5% reduction in diabetes progression observed
Treatment Options for Low Testosterone
When hypogonadism is confirmed through proper diagnostic evaluation, several treatment approaches may be considered based on individual patient factors, treatment goals, and fertility considerations.
Testosterone Replacement Therapy (TRT)
Direct testosterone supplementation is the most common approach for symptomatic hypogonadism:
- Injectable Testosterone (Cypionate/Enanthate): Administered every 1-2 weeks; provides reliable testosterone restoration with flexible dosing
- Transdermal Gel/Cream: Daily application provides steady hormone levels; requires attention to transfer risk
- Testosterone Pellets: Subcutaneous implants lasting 3-6 months; requires minor procedure for insertion
- Oral Testosterone (Kyzatrex®): FDA-approved oral option; taken twice daily with food
Fertility-Preserving Alternatives
For men concerned about fertility, alternatives to direct testosterone replacement may be considered:
- Clomiphene Citrate: Selective estrogen receptor modulator that stimulates endogenous testosterone production; preserves fertility
- Enclomiphene: The trans-isomer of clomiphene; stimulates natural testosterone production without estrogenic side effects; maintains spermatogenesis
- Human Chorionic Gonadotropin (hCG): LH analogue that stimulates testicular testosterone production; often used with TRT to maintain fertility and testicular volume
Important Treatment Considerations
The Endocrine Society recommends against testosterone therapy in men with:
- Desire for fertility in the near term (unless fertility-sparing protocols are used)
- Untreated or poorly controlled prostate cancer
- Breast cancer
- Uncontrolled heart failure
- Hematocrit >50% without intervention
Lifestyle Factors That Influence Testosterone
Before or in addition to medical therapy, optimizing modifiable lifestyle factors can significantly impact testosterone levels:
Weight Management
Obesity is strongly associated with low testosterone through multiple mechanisms: increased aromatase activity in adipose tissue converts testosterone to estrogen, and excess body fat promotes inflammation that suppresses the HPG axis. Research shows that weight loss of 5-10% can significantly increase testosterone levels.
Exercise
Resistance training is particularly effective at supporting testosterone production. A study in The World Journal of Men's Health found that high-intensity interval training (HIIT) was superior to steady-state cardio for improving testosterone in men with erectile dysfunction.
Sleep Quality
Testosterone is primarily produced during sleep. Studies demonstrate that restricting sleep to 5 hours per night for one week reduces testosterone levels by 10-15%. Prioritizing 7-9 hours of quality sleep supports optimal hormone production.
Stress Management
Chronic stress elevates cortisol, which directly suppresses testosterone production. Effective stress management techniques—whether exercise, meditation, or other approaches—can help maintain healthy hormone balance.
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Peer-Reviewed References
- Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715-1744. doi:10.1210/jc.2018-00229
- Lincoff AM, Bhasin S, Flevaris P, et al. Cardiovascular safety of testosterone-replacement therapy. N Engl J Med. 2023;389:107-117. doi:10.1056/NEJMoa2215025
- Dupree JM, et al. What is a normal testosterone level for young men? Rethinking the 300 ng/dL cutoff for testosterone deficiency in men 20-44 years old. J Urol. 2022;208(6):1228-1236. doi:10.1097/JU.0000000000002928
- Jayasena CN, Anderson RA, Llahana S, et al. Society for Endocrinology guidelines for testosterone replacement therapy in male hypogonadism. Clin Endocrinol (Oxf). 2022;96(2):200-219. doi:10.1111/cen.14633
- Snyder PJ, Bauer DC, Ellenberg SS, et al. Testosterone treatment and fractures in men with hypogonadism. N Engl J Med. 2024;390:203-211. doi:10.1056/NEJMoa2308836
- Snyder PJ, Bhasin S, Cunningham GR, et al. Lessons from the Testosterone Trials. Endocr Rev. 2018;39(3):369-386. doi:10.1210/er.2017-00234
- Zitzmann M, et al. Cardiovascular safety of testosterone therapy—Insights from the TRAVERSE trial and beyond: A position statement of the European Expert Panel for Testosterone Research. Andrology. 2025. doi:10.1111/andr.70062
- Corona G, Rastrelli G, Maggi M. Cardiovascular safety of testosterone replacement therapy in men: an updated systematic review and meta-analysis. Expert Opin Drug Saf. 2024;23(5):565-579. doi:10.1080/14740338.2024.2337741
- Corsini C, Pozzi E, Belladelli F, et al. Age-related decline in total testosterone levels among young men: insights from a large single-center observational study. Int J Impot Res. 2025. doi:10.1038/s41443-025-01029-2
- Nassar GN, Leslie SW. Physiology, Testosterone. StatPearls [Internet]. 2023. PMID: 30285384
- Yeap BB, et al. Low testosterone levels linked to shorter life span. Ann Intern Med. 2024. Published online May 14, 2024
- Yeo JK, Cho SI, Park SG, et al. Which exercise is better for increasing serum testosterone levels in patients with erectile dysfunction? World J Mens Health. 2018;36(2):147-152. doi:10.5534/wjmh.17030
