The primary male sex hormone that drives muscle, bone density, sexual function, mood and metabolic health — and what happens when levels decline.
Testosterone is the primary male sex hormone — an androgen produced mainly in the Leydig cells of the testes (approximately 95%) with a small contribution from the adrenal glands. It is the central regulator of male physiology: driving muscle development, bone density, sexual function, red blood cell production, mood, cognitive performance and metabolic health. Testosterone peaks in early adulthood (typically ages 18–25) and declines at approximately 1–2% per year from around age 30. Not all testosterone is biologically active — only “free” testosterone (unbound to carrier proteins) exerts effects on target tissues. Understanding total testosterone, free testosterone and SHBG together gives a complete hormonal picture.
Why total testosterone alone doesn't tell the full story
| Form | Role | Too Low | Too High |
|---|---|---|---|
| Total Testosterone | The sum of all circulating testosterone — bound and unbound. Standard first-line test but not always clinically meaningful alone. | Fatigue, low libido, muscle loss, depression, brain fog | Acne, aggression, polycythaemia, testicular atrophy (if exogenous) |
| Free Testosterone | Biologically active testosterone — unbound to SHBG or albumin. Drives most of testosterone's physiological effects. | Symptoms of low T despite 'normal' total T; common with high SHBG | Less common; may occur with very high total T or low SHBG |
| SHBG (Sex Hormone-Binding Globulin) | Carrier protein that binds testosterone, rendering it inactive. High SHBG = low free T even when total T is normal. | More free testosterone available — seen in obesity, insulin resistance | Reduces free testosterone — seen with age, hypothyroidism, some medications |
Testosterone imbalance in men primarily presents as deficiency (hypogonadism), though elevated levels — usually from exogenous sources — carry their own risks.
The testes fail to produce adequate testosterone despite normal or elevated LH/FSH from the pituitary. Causes: Klinefelter syndrome, orchitis, trauma, chemotherapy, radiation. Blood test: low T + high LH/FSH.
The pituitary fails to send adequate LH signal to the testes. Causes: obesity, hyperprolactinaemia, pituitary tumours, opioid use, anabolic steroid history. Blood test: low T + low/normal LH/FSH.
Testosterone gradually declines from age 30. When symptomatic, this is called late-onset hypogonadism or andropause. Symptoms are often attributed to 'ageing' and dismissed — but treatment is available.
Testosterone above physiological levels — from TRT dosing errors or anabolic steroid misuse. Risks: polycythaemia, cardiovascular strain, testicular atrophy, infertility, acne, mood disturbance.
Testosterone is converted to estradiol (the primary estrogen) by the enzyme aromatase — and this conversion is essential for male health. Men need estradiol for bone density, cardiovascular protection, libido and brain function. Problems arise when the testosterone-to-estradiol ratio becomes imbalanced.
Excess body fat dramatically increases aromatase activity — converting more testosterone to estradiol. This raises E2, reduces free T and worsens symptoms of low T, creating a self-reinforcing cycle.
Too little estradiol (from aromatase inhibitor overuse or very low T) causes bone loss, impaired libido, joint pain and cardiovascular harm. Men need estrogen — just in appropriate amounts.
Healthy testosterone with proportionate estradiol conversion supports bone, mood, libido and cardiovascular health. Managing body composition is the most effective way to optimise this ratio naturally.
Testosterone is far more than a sex hormone. It is the central regulator of male physiology — governing muscle mass, bone density, energy levels, mood, cognitive function, cardiovascular health and sexual function. While testosterone is most often discussed in the context of libido and gym performance, its systemic effects are profound and far-reaching. Understanding testosterone is one of the most important steps any man can take for his long-term health.
Testosterone is produced primarily in the Leydig cells of the testes, under stimulation from luteinising hormone (LH), which is itself regulated by the hypothalamic-pituitary-gonadal (HPG) axis. This feedback system means that disruptions at any level — from chronic stress suppressing GnRH release, to a pituitary tumour reducing LH output, to primary testicular failure — can result in low testosterone.
Testosterone levels peak in early adulthood and decline gradually from approximately age 30 at a rate of 1–2% per year. This age-related decline is normal, but for a significant proportion of men, the decline becomes clinically meaningful — producing symptoms of fatigue, low libido, loss of muscle, increased body fat, depression and cognitive changes that are frequently dismissed as “normal ageing”. Late-onset hypogonadism is an underdiagnosed condition in South Africa, partly due to limited access to specialist men’s health services and cultural barriers to seeking help.
For South African men, the burden is compounded by high rates of obesity, metabolic syndrome and psychological stress — all of which suppress testosterone production. The good news is that lifestyle interventions — particularly resistance training, improved sleep, weight loss and stress management — can meaningfully raise testosterone levels without medical intervention in many men. Where clinical hypogonadism is confirmed, testosterone replacement therapy (TRT) is safe and effective when properly managed by a qualified specialist.
HealthLab’s Men’s Health section provides comprehensive, evidence-based information on testosterone testing, treatment options, natural optimisation strategies and the broader context of male hormonal health. Whether you’re experiencing symptoms of low T, exploring TRT for the first time, or simply want to understand your hormones better, our resources are here to support you — alongside our directory of HPCSA-registered men’s health specialists across South Africa.
