testosterone

basic

Here you will learn the basics – explained simply and understandably.

What is testosterone?

Testosterone is the most important of the male sex hormones , also known as androgens. These include testosterone, DHT, DHEA, androstenedione, and androsterone.

In men, the testes produce about 6-7 mg of testosterone daily. Testosterone is also produced in the adrenal glands, but this accounts for only a small portion (<5%) of the body's testosterone production. ¹

Women also have their own testosterone: 50% of it is produced directly in the ovaries and adrenal glands, and the other half is converted from androgen precursors. However, women have significantly lower testosterone levels than men. ²

Alternative names for testosterone

In colloquial language, testosterone is often shortened to "testo" or "T." It is often referred to as the "male hormone" or "male sex hormone." In older texts, the term "testicular hormone" is also found, based on the Latin origin of the word (testis = testicle).

Chemically, testosterone can also be described as 17β-hydroxy-4-androsten-3-one (C ₁₉ H ₂₈ O ₂ ). ³

There are various trade names for medical testosterone preparations such as Tostran®, Testoviron® or Andriol®.

What function does testosterone have in the body?

Testosterone is crucial for a man’s physique and sexual function:

• During puberty, the hormone promotes physical maturation: testicles and penis grow, sperm production begins, and potency and libido awaken. The growth of the larynx leads to voice change, beard and body hair sprout, and sebaceous gland production is stimulated. Furthermore, rising testosterone levels trigger a pubertal growth spurt, particularly an increase in muscle mass: in 15-year-old boys, muscle mass accounts for an average of 50% of body weight, compared to only 43% in girls of the same age. ⁴
• In adult men, the hormone ensures the maintenance of physique, potency, and libido: Testosterone influences the process of blood formation, bone stability, and body mass composition, as well as erectile function and ejaculate volume. ⁵ It also affects cognition, particularly spatial perception. ⁶ It also influences the psyche—especially sexual desire, but also general mood and drive. ⁷

Testosterone also plays an important role in women, both during puberty and adulthood. It always acts in dynamic balance with the female sex hormones (estrogen and progesterone). Testosterone is particularly important in blood formation and muscle and bone development; it also affects the skin, hair follicles, and sebaceous glands. It also serves as an important starting material for the production of estradiol. ⁸

How is testosterone regulated in the body?

Testosterone production in men is primarily regulated by the interaction of the brain, pituitary gland, and testes. Various hormones serve as messengers.

The brain, or more precisely the hypothalamus , releases GnRH (gonadotropin-releasing hormone) at rhythmic intervals. GnRH stimulates the pituitary gland to produce LH (luteinizing hormone). LH activates the Leydig cells in the testes to produce testosterone. A sufficient amount of testosterone causes a negative feedback loop, meaning it inhibits further LH release in the pituitary gland and thus also the activity of the Leydig cells. Other hormones are also involved in the fine-tuning of this process, particularly FSH (follicle-stimulating hormone), activin, and inhibin. ⁹

Similar regulatory circuits also operate in other organs: ACTH (adrenocorticotropic hormone) controls testosterone production in the adrenal glands in men and women, while LH regulates this process in the ovaries of women. ¹⁰

The complex mechanisms of testosterone production can be influenced by certain diseases and medications as well as by lifestyle factors (including diet, exercise and sleep).

Free testosterone vs. total testosterone: What's the difference?

Testosterone is transported throughout the body in the blood. During transport, it is bound to two other proteins: albumin and sex hormone-binding globulin (SHBG). Only a very small portion (2%) of testosterone remains free or unbound in the blood. ¹¹

Testosterone tests can therefore determine two different values:

• the free testosterone, measured in pg/ml or pmol/l – i.e. picograms or picomoles
• the total testosterone, measured in ng/ml or nmol/l – i.e. nanograms or nanomoles (1 nanogram = 1000 picograms, 1 nanomole = 1000 picomoles) ¹²

How does testosterone affect my mood and behavior?

Testosterone is a key factor in a man's quality of life : It not only influences libido and sexual experience, but also has a positive effect on general well-being, self-confidence, and motivation. Testosterone promotes the pursuit of social status and, depending on self-image, can also increase risk-taking. At the same time, the hormone has an anxiolytic effect—it influences alertness, reward processing, and stress resilience.

A testosterone deficiency, on the other hand, can increase feelings of anxiety, trigger depressive symptoms, and make you feel sluggish and listless. ¹³ The perception of physical changes resulting from testosterone deficiency can further reinforce this negative mood.

Good to know: The connection between testosterone and behavior works both ways, meaning you can actively influence your testosterone levels .

What happens if I have too much testosterone?

Testosterone is an important factor for sperm production in men – but excessively high testosterone levels can suppress spermatogenesis . This sounds paradoxical, but it is based on the negative feedback mechanism in the hormonal control circuit:

The brain stimulates the pituitary gland to secrete LH (luteinizing hormone) and FSH (follicle-stimulating hormone). LH activates testosterone production in the Leydig cells of the testes, and FSH stimulates spermatogenesis in the Sertoli cells of the testes. High levels of testosterone cause a negative feedback loop, meaning they inhibit further hormone secretion from the pituitary gland and thus also spermatogenesis.

• Important to know: If a testosterone test shows noticeably high values, this may indicate a serious illness – medical advice is always recommended! ¹⁴
• Taking testosterone supplements without medical supervision can also lead to elevated hormone levels, which not only limit fertility but also pose numerous other health risks. ¹⁵

An excess of androgen in women can alter the appearance of the skin, increase body hair (hirsutism), and cause scalp hair loss (androgenetic alopecia). Changes to the breasts and genitals, as well as reduced fertility, are also possible. ¹⁶

What happens if I have a testosterone deficiency?

Too low testosterone levels can significantly impair a man’s quality of life.

On the one hand, psychological well-being is negatively affected: testosterone deficiency leads to bad moods, even depressive moods, reduced drive and lack of sexual desire.

On the other hand, physical performance decreases, and potency and muscle strength decline. Visible changes also occur: increased body fat, less beard growth and body hair, and in some cases, a reduction in penis and testicles and/or an enlargement of the mammary glands (gynecomastia). Invisible, but equally serious for men's health, are the effects of testosterone deficiency on the prostate (atrophy), metabolism, blood formation (anemia), and bone density (increased risk of osteoporosis). ¹⁷

Advanced

This section will deepen your knowledge and give you more detailed insights.

When is my testosterone level highest and when is it lowest?

Testosterone levels in men change throughout the day. Testosterone levels are highest in the morning , then fall by up to 35% throughout the day. They are lowest in the late evening, before rising again around midnight. ¹⁸

In women, testosterone levels depend not only on the time of day, but also, and above all, on the cycle. ¹⁹

How can I influence my hormone levels?

Nutrition, exercise, regeneration – these are the three most important lifestyle factors with which you can actively influence your testosterone levels.

• With a balanced diet, you provide your body with the building blocks for all metabolic processes, including testosterone production. Pay particular attention to an adequate calorie intake, as obesity , especially an excess of visceral fat, is one of the main factors for low testosterone levels in older men. ²⁰
• Regular exercise can boost testosterone production . ²¹ This applies to both traditional strength training ²² and endurance sports ²³ , and even gentle yoga stretching leads to a measurable improvement. ²⁴
• On the one hand, regeneration means a restful night's sleep. On the other hand, active relaxation techniques are particularly useful during stressful periods, as chronic stress can significantly impair testosterone levels. ²⁵ The reason for this is that the production of the stress hormone cortisol is in direct competition with testosterone production.

Which foods can affect my testosterone levels?

Foods rich in zinc should be regularly included in every man's diet, as zinc contributes to maintaining normal testosterone levels in the blood. ²⁶ Good sources of this trace element include fish, shellfish, poultry, beef, wheat bran, oatmeal, legumes, nuts, seeds, and dairy products. ²⁷ If necessary, you can also optimize your zinc intake with dietary supplements.

Some scientific studies also show a positive association between testosterone and omega-3 fatty acids , particularly docosahexaenoic acid (DHA), which are mainly found in marine fish oils ²⁸ , as well as vitamin D , which is also found in oily fish but is largely produced in the skin under the influence of sunlight ^{29 .}

In general, a Mediterranean low-carb diet with plenty of vegetables, whole grain products, lean meat, fish, and vegetable fats has a positive effect on testosterone levels. ³⁰

Although cholesterol is a basic substance for testosterone production, increased cholesterol intake does not increase testosterone levels.

Excessive alcohol consumption lowers testosterone levels. A small amount of alcohol, however, can temporarily increase testosterone levels because the breakdown of alcohol in the liver causes increased activity of detoxification enzymes. ³¹

How does testosterone change with age?

Male testosterone levels change significantly over the course of life:

• In newborns, it almost reaches adult levels, but then adjusts to the level of female infants by the 6th month of life. ³²
• During puberty it increases about tenfold (prepubertal 0.28-0.49 nmol/l → pubertal 2.8-6.3 nmol/l).
• In adult men, the reference range for total testosterone is 9.0–34.7 nmol/l. ³³
• With advancing age , the body's own hormone production declines; by the age of 60-70, testosterone levels are only half what they were in younger years. ³⁴

In women, testosterone also increases with the onset of puberty and decreases with the onset of menopause. ³⁵

How does sleep affect my testosterone levels?

In men, a large portion of the daily amount of testosterone is released during sleep. Sleep interruptions and reduced sleep quality (e.g., due to sleep apnea) are associated with reduced testosterone levels. Even in young, healthy men, just one week of only 5 hours of sleep a night can reduce testosterone levels by 10-15%. ³⁶

What false myths are there about testosterone?

There are many myths or rather half-truths circulating about the male hormone testosterone, which we would like to clarify here:

• " Testosterone makes you aggressive " – High testosterone levels were often associated with excessive aggression in previous studies. Current research, however, shows a more complex relationship: Testosterone promotes the pursuit of social status – but how much risk one takes and whether one relies more on aggressive or prosocial behavior depends, in part, on one's self-image. ³⁷
• " Bald men have a lot of testosterone " – Androgens are indeed involved in hair growth, but the extent and pattern of hair loss are primarily influenced by genetic factors and the individual distribution of androgen receptors. Furthermore, it is not testosterone itself that affects the hair, but rather its conversion product, DHT. ³⁸ The idea of ​​using medication to prevent this conversion process and thus hair loss is obvious, but is associated with numerous side effects. ³⁹
• “ Testosterone makes you taller ” – During puberty, testosterone is crucial for height growth, as well as the growth of the testicles and penis. ⁴⁰ In adult men, however, there is no correlation between testosterone and height ⁴¹ or testosterone and penis length. ⁴²

Expert

This is about advanced concepts for a deeper understanding.

Which substances are involved in the formation of testosterone?

The basic substance for testosterone production is cholesterol, which is released from fat droplets in the cytoplasm. The conversion occurs via several intermediate steps:

• Cholesterol → Pregnenolone , under the influence of the enzyme cytochrome P ₄₅₀ SSC, whose release is activated by the luteinizing hormone
• Pregnenolone → Androstenedione , whereby the synthesis can proceed via progesterone and 17-alpha-hydroxyprogesterone, or via 17-alpha-hydroxypregnenolone and dehydroepiandrosterone (DHEA)
• Androstenedione → Testosterone ⁴³

However, it would be wrong to believe that a high-cholesterol diet increases testosterone levels. ⁴⁴

What substances are produced from testosterone?

Testosterone exerts its effect in some cases directly (e.g. in muscle tissue), but mostly indirectly, i.e. after conversion into other substances:

• Testosterone → estradiol , which primarily affects the central nervous system, testes, bones, adipose tissue, and endothelium. The conversion is catalyzed by the enzyme aromatase.
• Testosterone → Dihydrotestosterone (DHT) , which primarily affects the prostate, skin, hair, and bones. The conversion is catalyzed by the enzyme 5-alpha reductase. ⁴⁵

Scientific sources