Testosterone production peaks in late adolescence and early adulthood, then gradually declines about 1% per year starting around age 30. This natural decline is different from hypogonadism (abnormally low testosterone), which can occur at any age due to testicular problems, pituitary dysfunction, medications, obesity, chronic illness, or other factors.
Testosterone exists in three forms in blood:
- Total testosterone measures all testosterone (both bound and free)
- Free testosterone measures the unbound, biologically active form (about 2-3% of total)
- Bioavailable testosterone includes free testosterone plus loosely bound testosterone
SHBG (Sex Hormone Binding Globulin) is a protein that binds and transports sex hormones. Higher SHBG means less free testosterone available for use. SHBG increases with age and certain conditions, which is partly why older men often have lower effective testosterone even if total testosterone looks reasonable.
DHEA (Dehydroepiandrosterone) and DHEA-S are precursor hormones produced mainly by the adrenal glands. Your body can convert them into testosterone and estrogen. DHEA levels also decline with age. Some people supplement DHEA, though evidence for benefits is mixed.
Androstanedione (androstanolone/DHT) is a metabolite of testosterone that's even more potent. It's responsible for some of testosterone's effects, particularly on the prostate and hair follicles.
FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone) come from the pituitary gland and control testosterone production. High FSH and LH with low testosterone indicates primary testicular failure (testicles aren't responding to the signal). Low or normal FSH and LH with low testosterone suggests secondary hypogonadism (pituitary or hypothalamus problem).
Cortisol is the primary stress hormone. The testosterone/cortisol ratio reflects the balance between anabolic (building) processes and catabolic (breaking down) processes. High cortisol relative to testosterone can indicate chronic stress and may affect muscle mass, recovery, and overall health.
Prolactin is a pituitary hormone that can suppress testosterone production when elevated. High prolactin can indicate pituitary tumors or result from certain medications.
Thyroid hormones (T4, free T4) affect metabolism and energy. Thyroid dysfunction can impact testosterone levels and overall vitality.
PSA (Prostate-Specific Antigen) is produced by the prostate gland. We covered this in detail in the Cancer category, but it's relevant to men's health more broadly as a screening and monitoring tool for prostate health.
AMH (Anti-Müllerian Hormone) in men indicates testicular function and can help assess fertility potential [Endocrine Society].
Men's health testing is crucial for healthspan because hormonal and metabolic changes profoundly affect quality of life, physical function, cognitive health, and disease risk throughout the aging process.
Low total testosterone with normal/high SHBG might mean adequate free testosterone (the active form). Calculate free testosterone or measure it directly for accurate assessment.
Low total and free testosterone with high FSH and LH indicates primary hypogonadism (testicular failure). The pituitary is signaling correctly, but testicles aren't responding.
Low total and free testosterone with low or normal FSH and LH suggests secondary hypogonadism (pituitary or hypothalamic problem). The signal from the brain to the testicles is inadequate.
Thyroid function affects testosterone metabolism. Hypothyroidism can lower testosterone. Evaluating thyroid hormones (TSH, free T4, TPO antibodies) alongside testosterone provides complete context.
DHEA-S levels declining with age is normal, but very low levels might indicate adrenal insufficiency. High levels can indicate adrenal tumors or PCOS (in women).
Pregnenolone is the precursor to all steroid hormones. Some practitioners measure it as part of comprehensive hormone assessment, though its clinical utility is debated.
Prolactin elevation suppresses testosterone production. Finding and treating the cause (often pituitary microadenoma or certain medications) can restore testosterone levels.
Estradiol in men comes partly from direct production and partly from testosterone conversion (aromatization). Very low estradiol (sometimes from excessive aromatase inhibitor use) causes problems: joint pain, bone loss, lipid changes. Mildly elevated estradiol is common with obesity (fat tissue converts testosterone to estradiol) and may not require treatment unless symptomatic.
PSA patterns matter:
- Stable PSA over time is reassuring
- Rising PSA warrants evaluation
- Very high PSA (>10-20 ng/mL) is concerning for prostate cancer
- PSA velocity (rate of rise) and PSA density (PSA relative to prostate size) provide additional context
Example 1: Age-related testosterone decline
- Total testosterone 350 ng/dL (low-normal)
- Free testosterone low
- Normal FSH and LH
- Normal prolactin and thyroid
- Symptoms: fatigue, reduced libido, difficulty maintaining muscle
- → Pattern consistent with age-related decline; might benefit from testosterone therapy after discussing risks/benefits
Example 2: Metabolic dysfunction affecting hormones
- Low testosterone
- Elevated cortisol (morning)
- Abnormal glucose/insulin
- Elevated estradiol
- Overweight/obese
- → Metabolic syndrome affecting hormones; lifestyle intervention is first-line treatment
Example 3: Primary hypogonadism
- Very low testosterone
- Very high FSH and LH
- Low AMH
- → Testicular failure; requires testosterone replacement
Example 4: Pituitary problem
- Low testosterone
- Low FSH and LH
- Elevated prolactin
- → Possible pituitary tumor; needs imaging and endocrine evaluation
What You Can Learn
Comprehensive men's health testing provides multiple valuable insights:
Common Questions
*This information is for educational purposes and is not a substitute for professional medical advice. Always consult with your healthcare provider about your specific health needs and test results.