How to read the numbers: Today’s average = common in today’s population – not a target or optimum · Risk = what to watch out for
Average decline over 40 years
Several studies describe a decline in average population testosterone over recent decades; its size varies between studies and is partly linked to rising obesity. The most you can do for your own levels is maintain a healthy weight, sleep well and train strength.
Decline after age 30
After thirty, men's testosterone gradually declines with age, but individual differences are large and lifestyle plays a major role. Regular strength training, enough sleep and limiting alcohol are among the most effective steps.
Below optimal after 45
Estimates of how many men over 45 have below-optimal testosterone depend on the cut-off and measurement method used, but it is a common finding. If you have fatigue or low libido, have a morning blood test and review the result with a doctor.
Testosterone is not just a "male hormone". It is an anabolic steroid that the female body produces too — only in smaller amounts. In men, it is made by the Leydig cells in the testes; in women, by the ovaries and adrenal glands. It is regulated by the hypothalamic–pituitary–gonadal axis.
The problem is not only the decline with age. It is also the speed of that decline. Studies show that testosterone levels in a 40-year-old man today are 15–20% lower than in a 40-year-old man in 1980. That is not ageing — that is environment and lifestyle.
Visceral belly fat is endocrinologically active — it produces aromatase, the enzyme that converts testosterone into oestradiol. The more visceral fat a man carries, the lower his testosterone and the higher his oestrogen.
What testosterone actually does
Testosterone regulates red blood cell production, bone density, muscle synthesis, mood, cognitive function, libido, erectile function and fat distribution. Low testosterone (hypogonadism) shows up as chronic fatigue, low mood, reduced muscle mass, visceral obesity, brain fog and low libido.
Why it is falling faster than in previous generations
Chronic stress raises cortisol, which competitively inhibits testosterone production. Lack of sleep — a single bad week lowers testosterone by 10–15%. A sedentary lifestyle, alcohol, plastics containing BPA/phthalates (xenoestrogens), excess weight and nutritional deficiencies (zinc, vitamin D, magnesium) are the main environmental causes.
Lab values — what to look for
The reference range used by most laboratories (10–35 nmol/L) is far too broad. The optimum for a vital man is 20–30 nmol/L total testosterone, with free testosterone above 300 pmol/L. SHBG (sex hormone-binding globulin) matters just as much — high SHBG reduces the amount of free testosterone available.
How to optimise testosterone naturally
Strength training 3–4× a week (especially squats and deadlifts) is the most powerful natural stimulus. Sleep 7–9 hours — 80% of daily testosterone production takes place during the REM phase. Reduce visceral fat, manage stress and eliminate plastics when eating and drinking. Zinc (15 mg/day), vitamin D (2,000–5,000 IU) and magnesium bisglycinate (300 mg in the evening) are clinically proven support.
When to consider TRT
TRT (testosterone replacement therapy) is indicated for confirmed hypogonadism — total T below 10 nmol/L with clinical symptoms. It is a medical decision that requires a thorough examination. The consequences of inappropriate TRT include testicular atrophy, erythrocytosis and cardiovascular risks. Fénix Methode will help you identify whether you need natural optimisation or a medical consultation.
