Thick body hair, muscle mass, and a deep voice – all thanks to one hormone? Today we give a brief overview of the male hormone testosterone, its functions, and how a possible deficiency may become noticeable.
Testosterone as a sexual drive – what’s behind it?
Testosterone is one of the body’s natural sex hormones and is the primary male sex hormone. It is produced in the testes and the adrenal cortex and fulfills a wide range of important functions. Throughout life, testosterone contributes to the development of male sexual characteristics and a typically male physical appearance, such as facial and body hair, muscle mass, and a deeper voice.
It also has a significant impact on the male brain, influencing motivation and cognitive performance. Testosterone affects libido as well: it stimulates sperm production and thus supports fertility.
Testosterone deficiency: What can be the causes?
When men feel that their sense of vitality or “masculinity” is declining, many different factors can be responsible. One possible explanation is a testosterone deficiency. But how does it develop, and how does it present itself?
Testosterone levels are regulated through a complex interaction between the hypothalamus, the pituitary gland, and the testes. Levels vary between individuals and can fluctuate throughout the day; for example, testosterone is typically highest in the morning and before noon. Various factors can also temporarily lower testosterone levels, including:
- significant overweight
- high alcohol consumption, drug or medication misuse
- prolonged fasting
- intense physical exertion
- psychological stress
- severe infections or chronic diseases such as type 2 diabetes
A healthy lifestyle can help avoid additional negative influences on testosterone production and action and may help reduce the risk of deficiency.
Scientific literature generally recommends diagnosing a deficiency when values fall below 3.48 ng/ml. Testosterone levels are measured through a blood test, although a single measurement is not sufficient for diagnosis. A testosterone deficiency may be congenital or acquired.
In general, a distinction is made between primary and secondary hypogonadism.
In primary hypogonadism, the causes lie directly in the testes, where the hormone is produced. If, on the other hand, the regulation of hormone production is disturbed at the level of the pituitary gland, this is referred to as secondary hypogonadism. Additional potential causes of low testosterone include severe burns, cancer treatments, or kidney insufficiency.
How do I recognize a possible testosterone deficiency?
Just as varied as the causes are the symptoms of testosterone deficiency. They can affect physical, psychological, and sexual well-being and vary depending on age, duration, and the extent of the deficiency. Possible symptoms include:
- delayed puberty
- small testes
- infertility
- reduced body hair
- enlargement of male breast tissue (gynecomastia)
- loss of lean body mass and reduced muscle strength
- decreased bone mineral density (osteoporosis)
- reduced sexual desire and activity
- erectile dysfunction (including reduced nighttime erections)
- hot flashes
- mood swings and fatigue
- sleep disturbances
- reduced cognitive performance
Many of these symptoms are nonspecific and are therefore often attributed to other conditions or to professional and personal stress. Not all affected individuals show the same symptoms or the same severity. Often, symptoms develop gradually over time.
If complaints persist or worsen, a testosterone deficiency may be present. In this case, a medical evaluation can provide clarity.
To take with you
Testosterone plays an important role in strength, energy, libido, mood, and overall well-being. A deficiency can affect many areas of life — but it does not have to be permanent. Many influencing factors, such as lifestyle, stress, or underlying conditions, can be treated or positively changed. Anyone who listens to their body’s signals and seeks medical advice when symptoms persist can actively support their health. With the right guidance, hormone balance can often be restored, allowing the positive effects of testosterone to re-emerge.
Further information on the topic can be found here:
Rojas-Zambrano J.G., Rojas-Zambrano A., Rojas-Zambrano A.F. (April 24, 2025) Impact of Testosterone on Male Health: A Systematic Review. Cureus 17(4): e82917. https://www.cureus.com/articles/358719-impact-of-testosterone-on-male-health-a-systematic-review
Buratto, J., Kirk, B., Phu, S., Vogrin, S., Duque, G. (2023). Safety and efficacy of testosterone therapy on musculoskeletal health and clinical outcomes in men: A systematic review and meta-analysis of randomized placebo-controlled trials. Endocrine Practice, 29(9), 727–734. https://doi.org/10.1016/j.eprac.2023.04.013
Zhang, Z., Kang, D., Li, H (2020). The effects of testosterone on bone health in males with testosterone deficiency: a systematic review and meta-analysis. BMC Endocr Disord 20, Articel 33. https://doi.org/10.1186/s12902-020-0509-6