Testosterone Levels by Age: What the Numbers Mean — and What They Don't

What does testosterone actually do in the body?

Testosterone is the primary androgen in people assigned male at birth, where it drives puberty, supports muscle and bone mass, regulates red blood cell production, influences mood and energy, and is required for sperm production. It is also present in people assigned female at birth, though at much lower concentrations, where even modest elevations can be clinically significant.

Clinicians most often measure testosterone when someone reports symptoms such as persistent fatigue, reduced sex drive, difficulty with erections, mood changes, loss of body hair, or unexplained loss of muscle or bone density. It is also part of fertility evaluations and monitoring of certain hormone conditions.

How do testosterone levels change across a lifetime?

Testosterone production rises sharply during puberty, peaks in the late teens and early twenties, then declines gradually through adulthood. Data from the Massachusetts Male Aging Study — a large population-based cohort that tracked over 1,000 men for 7 to 10 years — found that total testosterone declined at roughly 0.8 percent per year of age cross-sectionally, while bioavailable (free and albumin-bound) testosterone declined closer to 2 percent per year longitudinally 1Ref 1Feldman HA, Longcope C, Derby CA, Johannes CB, Araujo AB, Coviello AD, Bremner WJ, McKinlay JB (2002).Age trends in the level of serum testosterone and other hormones in middle-aged men: longitudinal results from the Massachusetts male aging study.Testosterone declines at roughly 0.8% per year cross-sectionally and bioavailable testosterone approximately 2% per year longitudinally in aging men.

This decline is a normal part of aging, not a disease in itself. A man in his late sixties or seventies may have measurably lower levels than he did at thirty, yet still fall well within a healthy range. The critical phrase is "within a range": reference intervals are deliberately wide because healthy, symptom-free men sit across the full span of them throughout their lives.

Why is a testosterone result harder to read than it looks?

Several factors make a single testosterone number difficult to interpret without clinical context.

Lab reference ranges differ. Methods vary between laboratories, so a value flagged low by one may not be by another. The Endocrine Society's 2018 clinical practice guideline recommends using a lower threshold of approximately 300 ng/dL (10.4 nmol/L) for total testosterone as one indicator of deficiency, but emphasizes this is a guideline, not an absolute cutoff 2Ref 2Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, Snyder PJ, Swerdloff RS, Wu FC, Yialamas MA (2018).Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline.Reference threshold of ~300 ng/dL; requirement for two morning draws; treatment reserved for men with both low levels and symptoms; free testosterone interpretation in altered protein-binding states. The AUA's 2018 guideline similarly uses 300 ng/dL as a threshold while emphasizing the need for two morning measurements before acting on a result 3Ref 3Mulhall JP, Trost LW, Brannigan RE, et al. (2018).Evaluation and Management of Testosterone Deficiency: AUA Guideline.AUA threshold of 300 ng/dL; requirement for two separate morning draws before diagnosis; evaluation framework for testosterone deficiency.

Total testosterone includes inactive hormone. Most standard tests measure total testosterone — the sum of hormone bound to sex hormone-binding globulin (SHBG), hormone loosely bound to albumin, and the small free fraction. Only the free and albumin-bound fractions are biologically active. A high SHBG level (common with aging, certain liver conditions, or hyperthyroidism) can make total testosterone look adequate while active hormone is actually low. Free testosterone measurement is less standardized but can tell a different story in men with altered protein binding 2Ref 2Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, Snyder PJ, Swerdloff RS, Wu FC, Yialamas MA (2018).Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline.Reference threshold of ~300 ng/dL; requirement for two morning draws; treatment reserved for men with both low levels and symptoms; free testosterone interpretation in altered protein-binding states.

Timing of the draw matters. Testosterone peaks in the early morning and is substantially lower by late afternoon — research has shown a roughly 20 to 25 percent difference between an 8 AM and 4 PM draw in younger men, an effect that diminishes but does not disappear with age 4Ref 4Brambilla DJ, Matsumoto AM, Araujo AB, McKinlay JB (2009).The effect of diurnal variation on clinical measurement of serum testosterone and other sex hormone levels in men.Testosterone is roughly 20-25% lower at 4 PM than at 8 AM in younger men; morning draw recommended for accurate clinical measurement. Both major guidelines recommend confirming any low result with a second morning draw before making clinical decisions 2Ref 2Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, Snyder PJ, Swerdloff RS, Wu FC, Yialamas MA (2018).Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline.Reference threshold of ~300 ng/dL; requirement for two morning draws; treatment reserved for men with both low levels and symptoms; free testosterone interpretation in altered protein-binding states3Ref 3Mulhall JP, Trost LW, Brannigan RE, et al. (2018).Evaluation and Management of Testosterone Deficiency: AUA Guideline.AUA threshold of 300 ng/dL; requirement for two separate morning draws before diagnosis; evaluation framework for testosterone deficiency.

What can push testosterone lower besides aging?

Several reversible or modifiable conditions can suppress testosterone independent of how the testes or pituitary are functioning.

Obesity. Excess adipose tissue contains the enzyme aromatase, which converts testosterone to estrogen. Higher estrogen then signals the hypothalamus and pituitary to reduce output, suppressing the whole axis. Body weight also lowers SHBG, further reducing total testosterone. A review of the mechanisms found that this functional hypogonadism in obese men is physiologically distinct from primary testicular failure — and that weight loss can partially reverse it 5Ref 5Ng Tang Fui M, Dupuis P, Grossmann M (2014).Lowered testosterone in male obesity: mechanisms, morbidity and management.Mechanisms by which obesity suppresses testosterone via aromatase, estrogen feedback, and SHBG reduction; functional hypogonadism distinct from primary testicular failure.

Obstructive sleep apnea. There is a well-documented association between untreated sleep apnea and lower testosterone, though a 2019 meta-analysis of 12 studies found that CPAP therapy alone did not reliably raise testosterone levels — suggesting that sleep apnea and obesity together, rather than apnea alone, drive much of the suppression 6Ref 6Cignarelli A, Castellana M, Castellana G, Perrini S, Brescia F, Natalicchio A, Garruti G, Laviola L, Resta O, Giorgino F (2019).Effects of CPAP on Testosterone Levels in Patients With Obstructive Sleep Apnea: A Meta-Analysis Study.CPAP alone was not associated with a significant change in total testosterone across 12 studies of 388 male patients with OSA; obesity likely the primary driver. Treating sleep apnea matters for overall health; its effect on testosterone specifically depends on the individual's circumstances.

Medications. Opioid analgesics are among the strongest suppressors: a 2020 systematic review and meta-analysis confirmed that opioids suppress testosterone centrally by inhibiting gonadotropin-releasing hormone (GnRH) secretion, with the prevalence of opioid-induced androgen deficiency in men ranging from 20 to 80 percent depending on dose, duration, and age 7Ref 7de Vries F, Bruin M, Lobatto DJ, Dekkers OM, Schoones JW, van Furth WR, Pereira AM, Karavitaki N, Biermasz NR, Zamanipoor Najafabadi AH (2020).Opioids and Their Endocrine Effects: A Systematic Review and Meta-analysis.Opioids suppress testosterone centrally via GnRH inhibition; prevalence of opioid-induced androgen deficiency ranges 20-80% depending on dose, duration, and age. Corticosteroids, certain antidepressants, antipsychotics, and some antihypertensives can also suppress the axis.

Other chronic illness. Type 2 diabetes, chronic kidney disease, HIV, and other systemic conditions are associated with functional testosterone suppression. Treating the underlying condition often improves levels without hormone therapy.

What happens when a clinician evaluates a low result?

If a first low result is confirmed on a second morning draw, the next step is understanding why — because the treatment and prognosis differ depending on the origin.

Primary hypogonadism (testicular origin) produces low testosterone alongside elevated LH and FSH, because the pituitary is signaling the testes normally but they are not responding. Causes include prior testicular injury, infection (such as orchitis), chemotherapy or radiation, genetic conditions like Klinefelter syndrome, or progressive age-related decline.

Secondary hypogonadism (pituitary or hypothalamic origin) produces low testosterone with low or inappropriately normal LH and FSH — the pituitary is not signaling strongly enough. Causes include a pituitary adenoma, hyperprolactinemia, chronic opioid use, obesity-driven suppression, or significant caloric restriction.

Additional tests often ordered alongside the hormone panel include LH, FSH, prolactin, and SHBG; thyroid function, complete blood count, and metabolic panel to rule out overlapping conditions; and in some cases imaging of the pituitary.

Treatment is not automatic. The Endocrine Society guideline is explicit that treatment should be reserved for men who have both a confirmed low level and symptoms attributable to deficiency — not for asymptomatic low numbers or for symptoms without biochemical confirmation 2Ref 2Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, Snyder PJ, Swerdloff RS, Wu FC, Yialamas MA (2018).Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline.Reference threshold of ~300 ng/dL; requirement for two morning draws; treatment reserved for men with both low levels and symptoms; free testosterone interpretation in altered protein-binding states. If treatment is considered, the fertility conversation must happen first: exogenous testosterone reliably suppresses sperm production, and a 2018 review confirmed azoospermia in approximately 65 percent of men within four months of use 8Ref 8Patel AS, Leong JY, Ramos L, Ramasamy R (2018).Testosterone Is a Contraceptive and Should Not Be Used in Men Who Desire Fertility.Exogenous testosterone causes azoospermia in approximately 65% of normospermic men within 4 months; fertility counseling required before initiating therapy. For men who want to conceive, testosterone therapy is generally avoided, and alternative approaches exist.

What should you bring to an appointment about this result?

A testosterone result is most useful when it arrives with context. Before or at the visit, it helps to have:

• The actual lab report, including the reference range used by that specific lab and the units (ng/dL or nmol/L)
• The time of day the blood was drawn
• A written list of all symptoms and how long each has been present
• All current medications, supplements, and herbal products
• Any previous testosterone results, for comparison over time
• Information about sleep quality, weight history, alcohol use, and relevant medical conditions

A clinician will typically ask about the time of the draw, symptoms, medications (particularly opioids or steroids), sleep quality, weight, and fertility goals before deciding whether the result is clinically meaningful.