Testosterone is a key hormone for male sexual function, body composition, bone health, and overall vitality. Many men experience a gradual decline in testosterone as they age, while others develop clinically significant low testosterone earlier due to health conditions that interfere with hormone production or signaling. Because symptoms such as fatigue, reduced libido, and low mood have many possible causes, a careful approach starts with understanding the biology and confirming deficiency with appropriate morning lab testing.
This article explains how testosterone is produced, why it declines, how clinicians diagnose testosterone deficiency, and what treatment options are commonly used when therapy is appropriate.
What Testosterone Does and How It Circulates
Testosterone supports libido, erectile function, sperm production, muscle protein synthesis, bone mineral density, and red blood cell production. It also influences fat distribution and insulin sensitivity and can affect mood and cognition.
In blood, testosterone is measured as total testosterone and, in selected cases, free testosterone. Total testosterone includes hormone bound to sex hormone binding globulin, bound to albumin, and unbound. Free and albumin bound testosterone are often considered the most biologically available. This matters because total testosterone can be misleading when sex hormone binding globulin is unusually high or low.
How Testosterone Is Made
Testosterone production depends on the hypothalamic pituitary gonadal axis.
The hypothalamus releases gonadotropin releasing hormone in pulses. The pituitary responds by releasing luteinizing hormone and follicle stimulating hormone. Luteinizing hormone stimulates Leydig cells in the testes to produce testosterone. The system works as a feedback loop: when testosterone rises, the brain reduces stimulation; when testosterone falls, stimulation increases.
Low testosterone can result from reduced testicular production, reduced brain signaling, or a combination of both.
Why Testosterone Declines With Age
Aging is associated with changes that can reduce testosterone, but the degree varies widely between men. In practice, health status often explains more of the difference than age alone.
Reduced Testicular Output
Over time, Leydig cells may respond less strongly to luteinizing hormone. Even with normal pituitary signals, testosterone production can decline. Vascular health, inflammation, and chronic disease can worsen this effect.
Changes in Brain Signaling
Some men develop secondary hypogonadism, meaning the hypothalamus or pituitary does not provide enough stimulation. Significant stress, under nutrition, chronic illness, and certain medications can blunt hormonal signaling and reduce luteinizing hormone output.
Rising Sex Hormone Binding Globulin
Sex hormone binding globulin tends to increase with age in many men. When it rises, more testosterone is bound and less is free. This is one reason clinicians sometimes evaluate free testosterone when symptoms are present but total testosterone is borderline.
Common Causes of Testosterone Decline Beyond Aging
Low testosterone is frequently influenced by modifiable factors. Identifying them is important because improving the underlying driver can reduce symptoms and improve overall health, whether or not testosterone therapy is used.
Excess Body Fat and Metabolic Dysfunction
Visceral fat is strongly associated with lower testosterone. Fat tissue can increase conversion of testosterone to estradiol, which may suppress the hypothalamic pituitary gonadal axis. Obesity is also linked to insulin resistance and inflammation, both of which can impair hormone signaling. Weight loss and resistance training can raise testosterone in some men and often improve symptoms even when testosterone does not fully normalize.
Type 2 Diabetes and Chronic Inflammatory States
Men with insulin resistance, type 2 diabetes, and chronic inflammatory conditions commonly have lower testosterone. Metabolic disease can suppress testosterone, and low testosterone can contribute to unfavorable body composition. A complete plan usually includes glycemic control, nutrition, and physical activity.
Sleep Disruption and Sleep Apnea
Testosterone follows a daily rhythm and is sensitive to sleep quality. Short sleep and fragmented sleep can lower morning testosterone and worsen symptoms such as fatigue and reduced libido. Obstructive sleep apnea can further aggravate this pattern. Treating sleep disorders can improve wellbeing and may improve testosterone status in some men.
Medication Effects
Long term opioid use is a recognized cause of secondary hypogonadism by suppressing brain signaling. Glucocorticoids can also reduce gonadotropins and lower testosterone, especially with prolonged use. A careful medication review is a standard part of evaluation.
Pituitary and Endocrine Disorders
Less commonly, low testosterone is driven by pituitary disorders, elevated prolactin, iron overload, or other endocrine conditions. Very low testosterone, low or inappropriately normal luteinizing hormone, headaches, visual symptoms, or infertility can signal the need for additional endocrine testing.
How Clinicians Diagnose Testosterone Deficiency
Diagnosis typically requires both consistent symptoms and consistently low testosterone on properly collected labs.
Symptoms may include reduced libido, erectile dysfunction, fewer morning erections, fatigue, depressed mood, decreased muscle mass, increased body fat, reduced physical performance, and decreased motivation. These symptoms are not specific to testosterone deficiency, which is why testing and clinical context matter.
Testing is usually done with early morning total testosterone, often repeated on a different day to confirm consistency. If total testosterone is borderline or if sex hormone binding globulin is likely abnormal, free testosterone may be assessed using an accepted method. Clinicians may also order luteinizing hormone, follicle stimulating hormone, prolactin, thyroid testing, iron studies, and metabolic markers when appropriate.
Acute illness, major stress, and poor sleep can temporarily lower testosterone. Interpreting results without accounting for these factors can lead to overtreatment.
Treatment Options for Low Testosterone
Treatment is individualized and should reflect symptoms, lab confirmation, underlying cause, fertility goals, and medical risk factors.
Address Reversible Contributors First
For many men, the first and most impactful step is improving factors that suppress testosterone or overlap with low testosterone symptoms. This commonly includes weight reduction when needed, resistance training, adequate sleep, evaluation for sleep apnea, and optimized management of diabetes and cardiovascular risk factors. These changes improve health regardless of whether hormone therapy is later used.
Testosterone Replacement Therapy When Appropriate
When symptoms are meaningful and low testosterone is confirmed on repeat testing, testosterone replacement therapy may be considered. The goal is to restore testosterone to a physiologic range and improve symptoms attributable to deficiency, with ongoing monitoring for safety.
For a local overview of evaluation and treatment planning, see Med Matrix information on Hormone Replacement Therapy in Portland, Maine. For a broader explanation of clinical care principles and follow up, visit the Med Matrix page on testosterone replacement therapy.
Common TRT Formulations
Clinicians select a formulation based on medical history, preference, cost, and practicality.
Injectable testosterone is widely used and can be cost effective. Transdermal gels are applied daily and can provide steady levels, but users must prevent transfer to others. Patches are another daily option but can irritate skin. Pellets provide longer lasting dosing but require a minor procedure and are slower to adjust.
Fertility Preserving Approaches
Exogenous testosterone can suppress luteinizing hormone and follicle stimulating hormone, which can reduce sperm production. Men who want children in the near term should discuss fertility goals before starting TRT. In selected cases, clinicians may use alternatives that support endogenous testosterone production or spermatogenesis, often under specialist guidance.
Monitoring, Safety, and Expectations
TRT can be effective for appropriately selected patients, but outcomes depend on the underlying cause and on lifestyle factors such as sleep and exercise.
What Improvements Are Most Consistent
Libido and sexual function often improve when low testosterone is the main driver. Energy, mood, and cognitive symptoms may improve, but the response varies. Body composition changes, such as increased lean mass and reduced fat mass, are more likely when therapy is paired with resistance training and nutrition support. Bone density can improve with sustained treatment in men with deficiency.
Why Monitoring Matters
Monitoring helps ensure testosterone stays in a physiologic range and helps detect side effects early. Clinicians often check testosterone levels, hematocrit, and other labs based on individual risk, and they assess blood pressure and overall cardiovascular risk factors. Prostate related evaluation is typically guided by age and personal risk.
A notable potential issue is erythrocytosis, an increase in red blood cell concentration. If hematocrit rises too high, dose adjustment or a change in formulation may be needed.
Putting the Science Into Practice
Testosterone decline is often influenced by more than age. Body fat, metabolic health, sleep quality, medications, and chronic disease can all lower testosterone or create symptoms that look like testosterone deficiency. A careful evaluation confirms whether deficiency is present and identifies contributors that can be improved.
When testosterone deficiency is confirmed and symptoms are meaningful, treatment options range from lifestyle based intervention to medically supervised testosterone therapy, with formulation choice and monitoring tailored to the individual. The most reliable outcomes come from evidence informed care, realistic expectations, and a plan that prioritizes safety, fertility goals, and long term health.
This information is educational and should not replace personalized medical care.
