Testosterone is an androgenic hormone that occurs in humans and other animals and plays a key role in multiple physiological processes. While often considered a ‘male’ hormone, testosterone is produced by both men and women in varying amounts.
In health and fitness contexts, testosterone is commonly associated with performance-enhancing synthetic forms of the hormone. But given the generational decline in male testosterone levels over the last two decades, male hormonal health is becoming an area of increasing importance for the general population.
Far beyond simply being responsible for typical male attributes, such as a deeper voice, facial hair and increased muscle mass, testosterone plays a pivotal role in male physical and mental health.
This article will explain what testosterone is, what role testosterone plays in the body and how it affects your health.
It will also look at the signs, symptoms and causes of low testosterone, and the steps you can take to maximise your hormonal health and testosterone levels naturally.
What is testosterone?
Testosterone is the primary sex hormone and anabolic steroid in men. Due to its growth-promoting properties, testosterone falls into a family of hormones known as androgens that are crucial for male sexual development and reproductive function. At puberty, these hormones also trigger the development of secondary male sexual characteristics, such as facial and body hair growth and deepening of the voice. Androgens also influence bone and muscle development and metabolism.
The human body produces testosterone via a system known as the hypothalamic-pituitary-adrenal axis (HPA), which connects the hypothalamus in the brain, the pituitary gland, and the gonads. In males, the Leydig cells in the testes primarily produce testosterone. When the body requires more testosterone, the hypothalamus secretes gonadotropin-releasing hormone (GRH), triggering the release of luteinising hormone (LH). Luteinising hormone travels through the blood and to the gonads, resulting in the production and secretion of testosterone into the blood.
While this is the primary physiological mechanism behind testosterone production, the body can also convert other compounds into testosterone. For example, your body can convert the adrenal hormone DHEA into testosterone in the pituitary gland. Equally, testosterone can convert to other hormones, like oestrogen, through the enzyme aromatase.
Healthy male testosterone levels fall between 10 and 30 nmol/L, depending on your age. Total testosterone measures the cumulative amount of testosterone within the body, which can be further broken down into two subtypes:
- Free testosterone and weakly bound testosterone (FWBT),
- Sex hormone-binding globulin-bound testosterone (SHBGT).
Free and weakly-bound testosterone – also known as ‘bioavailable’ testosterone – reflects an individual’s biologically active, circulating testosterone. FWBT includes free testosterone and testosterone bound to albumin, a protein in human blood that acts as a carrier for steroid hormones.
FWBT does not include sex hormone-binding globulin-bound testosterone. This type of testosterone ‘piggybacks’ onto sex hormone-binding globulin, a protein made in the liver that binds to sex hormones found in men and women. These hormones are oestrogen, dihydrotestosterone (DHT), and testosterone, which SHBGT carries through the blood.
However, the first form, FWBT, has what is known as a ‘low affinity’, meaning that its bonds can be broken relatively easily, thereby freeing the testosterone ready for use. However, in SHBGT, the bonds are far stronger, meaning that the body cannot tap into these reserves as easily. Therefore, in clinical settings, low testosterone typically refers to low levels of FWBT rather than SHBGT.
What does testosterone do?
While most people first think of bulging muscles when they hear the word testosterone, it plays a far more complex role than simply increasing muscle mass. In general, testosterone has two main effects on the body. The first is ‘anabolic’, referring to a series of metabolic pathways that construct molecules from smaller units. Anabolism is the building-up aspect of metabolism, whereas ‘catabolism’ refers to breaking down. In male physiology, its effects include:
- Skeletal development
- Muscle mass growth
- Increased red blood cell count
- Enhancing metabolic health (insulin sensitivity, fat metabolism, cholesterol levels etc.)
The second effect is ‘androgenic’, which refers to any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. These processes include:
- Male sex anatomy development (penis, testes, etc.)
- Facial, pubic, and body hair growth
- Deepening of the voice
- Body fat distribution (male-dominant versus female-dominant patterns)
- Sperm production
Interestingly, testosterone impacts men differently throughout their life. Up until the age of around 11, both sexes have relatively similar testosterone levels. However, during puberty, the difference in the hormonal profiles between males and females becomes more pronounced, resulting in physical and behavioural differences.
At this point, testosterone contributes to developing sperm-producing tissues in the testicles, growth of the jawline and Adam’s apple, an increase in muscle strength and size, deepening of the voice, stature and broadening of the shoulders.
Once puberty concludes, testosterone maintains the difference in physical appearance between men and women, supports male sexual function, and influences general health. Testosterone’s effects for adult men include maintaining muscle size and strength, sex drive, metabolic health (such as insulin sensitivity, cholesterol metabolism and red blood cell production), bone mineral density, and healthy sperm production.
Beyond its physical effects, research shows that testosterone can influence male behaviour, with links to aggression, competitive behaviour, and partner seeking,. The relationship between testosterone and behaviour seems to be via its interactions with dopamine, a neurotransmitter that transmits messages between brain cells in response to pleasurable experiences.
Testosterone influences behaviour by sensitising areas in the brain that use dopamine, increasing the strength of dopamine’s effects. As a result, testosterone seems to make men more impulsive and responsive to pleasurable stimuli. This increased impulsivity is, in part, why men statistically have a higher propensity towards high-risk behaviours and are more likely to abuse drugs, commit criminal behaviour, or even commit suicide,.
The male ‘menopause’
Ageing is a natural process that initiates various physiological changes. However, for men, ageing is one factor that significantly alters testosterone production and management. Research shows that approximately 40% of men over the age of 45 have low testosterone. From a man’s mid-thirties, average testosterone levels begin to drop by around 1-2% each year, a phenomenon you may have heard referred to as ‘the male menopause’ or, in clinical terms, the ‘andropause.’
This decline in natural testosterone production is a natural process that starts from the late twenties and thirties, triggered by a series of changes.
- The testicles naturally begin to produce less testosterone with age
- Lowered testicular testosterone means the hypothalamus produces less gonadotropin-releasing hormone (GnRH)
- Lowered GnRH causes the pituitary gland to produce less luteinising hormone (LH).
- Testosterone production decreases because of lowered LH levels.
Signs and symptoms of low testosterone
While the natural decline in testosterone doesn’t cause noticeable symptoms for many men, significant decreases may cause:
- Low sex drive
- Fewer spontaneous erections
- Erectile dysfunction
- Lowered sperm count or volume
- Difficulty sleeping
- Unusual loss of muscle and bone density
- Unexplained weight gain
However, the importance of ageing as a factor in testosterone production may be overestimated as these statistics do not account for lifestyle and behavioural factors. For example, we know that diet, exercise, sleep, and overall lifestyle impact natural testosterone levels.
Another critical detail is that only around 10% of men over 45 with clinically low testosterone present symptoms. Even when doctors prescribe testosterone replacement therapy to older men with low levels, their symptoms don’t always change. So, while testosterone tends to decline with age, adverse outcomes are not inevitable. Therefore, if you’re a man feeling the impact of ageing, low testosterone may be a catalyst but not the only cause.
When testosterone is clinically low, it can also reduce and impair male physical characteristics. Low testosterone levels often translate to alterations in body fat distribution and increased fat storage in typically female storage sites, such as the thighs, hips and breast tissue (think, the dreaded ‘man boobs’). Such changes are also accompanied by decreased muscle size and strength and reduced facial and body hair.
Low testosterone increases the risk of heart disease, high blood pressure, high cholesterol, and type 2 diabetes, a cluster of conditions that fall under the umbrella term ‘metabolic syndrome’. It is also estimated that over one-third of men with type 2 diabetes have low testosterone.
It is important to qualify that testosterone levels affect men differently. Two men could have the same testosterone levels and feel completely different. Whereas one man with low testosterone could feel lethargic and depressed, another may feel relatively healthy, happy, and fit. As a result, even if a man is diagnosed with clinically low testosterone, he may not always experience these symptoms and side effects.
Diagnosing low testosterone
If you’re concerned about your testosterone levels, your best option is to visit your doctor for further investigation or take a blood test. It’s also important to remember that testosterone is affected by various factors such as diet, sleep, time of day, fitness and certain medications. As a result, you may need to take tests at regular intervals to monitor your testosterone levels.
The medical term for low testosterone in men is hypogonadism, classified as ‘primary’ or ‘secondary’. Primary hypogonadism occurs when the testes don’t produce testosterone efficiently. In contrast, secondary hypogonadism occurs when the brain and hypothalamus don’t correctly signal testosterone production.
Clinical diagnosis of low testosterone is typically confirmed via a blood test, known as a serum testosterone test, which measures the total testosterone in your blood. A medical diagnosis of low testosterone usually also includes an analysis of symptoms and lifestyle factors. Testosterone is deemed low if it falls below the lower end of the range for your age group.
Testosterone replacement therapy (TRT) is currently the only treatment for low testosterone. TRT provides synthetic testosterone to replace the levels your body doesn’t produce, which can come in the form of gels, creams, patches, injections, and pellets surgically implanted under the skin.
If you have hypogonadism, TRT can help to improve symptoms, including:
- Improving sexual function
- Boosting sperm count and volume
- Increasing levels of other hormones that have a close relationship with testosterone, including prolactin (heavily involved in the production of LH and testosterone secretion).
Doctors may also prescribe TRT to improve hormonal imbalances resulting from:
- Autoimmune conditions
- Genetic disorders
- Infections or damage to sexual organs
- Undescended testicles
- Radiation therapy
- Surgery to sexual organs
If your testosterone levels fall slightly towards the lower end of the healthy range, it’s unlikely you will need TRT. However, if you are concerned about your testosterone levels, speak to your doctor or healthcare provider, who will discuss the best options for you.
Non-age-related causes of low testosterone
Testosterone is a sex hormone that is highly sensitive to outside influences and can be negatively affected by genetics and ill health. The mechanisms driving hypogonadism include genetic diseases, such as undescended testicles, Klinefelter’s syndrome, and Kallmann syndrome. Several chronic diseases can impair testosterone production, including hemochromatosis, cancer treatment, pituitary disorders, inflammatory diseases, and HIV/AIDS. Medications, such as anti-depressants, opioids, antihistamines, and statins, may also negatively impact testosterone levels.
However, far and away, the biggest and most controllable factor is lifestyle. Sleep, stress, and body composition play a major role in testosterone production and are particularly powerful triggers for secondary hypogonadism. For example, stress inhibits the production of gonadotropin-releasing hormone, thereby preventing the hypothalamus from triggering testosterone production.
Testosterone production can also be affected by blunt trauma to the testicles, caused by direct impact in 85% of instances. In addition, excessive heat and constrictive underwear can interfere with testosterone levels, as higher temperatures can negatively impact testicular function. Blunt trauma to the head can also damage the parts of your brain that tell your testes to produce testosterone.
Lifestyle factors, such as sleep, stress and body composition, have a significant role in testosterone production.
How can you naturally boost testosterone?
Evidence consistently demonstrates the importance of lifestyle factors in managing and increasing testosterone levels.
1. Improve your body composition
Research indicates that improving body composition through fat loss has a noticeably positive impact on obesity-related low testosterone,. One study monitored T levels in male participants and found that the prevalence of low testosterone halved after losing 10% and more of their total body weight through diet and exercise.
2. Manage stress
Stress is a factor that affects the body’s ability to manage various aspects of physiology, and testosterone is no exception. Men with low testosterone levels are statistically more likely to lead highly stressful lives, and studies even show that the mere anticipation of stress can decrease testosterone production. Stress can also indirectly impact testosterone by triggering unhealthy coping mechanisms, such as drinking, binge eating, and drug abuse. So, if you’re concerned about your T levels, setting aside time for stress management, such as meditation, journaling, and relaxation, is a crucial pillar to support your hormonal health.
3. Prioritise resistance training and physical activity
Research shows that men who remain physically active through life have higher testosterone levels. Of all forms of exercise, resistance training seems to be the most beneficial for boosting testosterone. So, if you’re not already following a structured resistance training program, there’s even more reason to get started.
4. Prioritise sleep and recovery
Sleep is one of the most potent tools for managing overall well-being as well as boosting your hormonal health. On average, men who sleep less have lower testosterone, with as little as one week of short sleep being sufficient to reduce your testosterone by 15%,. Most adults need somewhere between 7-9 hours of sleep per night, so if you’re not achieving this, focus on improving your sleep hygiene.
5. Improve your dietary quality and plug nutritional gaps with supplementation
While diet impacts hormonal balance primarily through weight management, nutrient deficiencies are also crucial in hormonal production. Zinc has proven links to male hormonal balance, with research showing that restricting zinc intake lowers testosterone. Equally, magnesium also appears to play a role in testosterone serum concentration and bioavailability. While the only way to fully determine nutrient deficiencies is via blood analysis, supplementing with UltraMag and Zinc NT can help provide your body with vital nutrients in a bioavailable form.
Resistance training, regular activity, diet, sleep and stress management all play a role in helping foster healthy testosterone levels.
Testosterone is a hormone that plays a crucial role in male health with wide-ranging physical, mental and behavioural effects.
While ageing brings an inevitable decline in sex hormone production, lifestyle and behaviour play a key role in modulating T levels. So, while you may not be able to stop the clock entirely, healthy lifestyle change through diet, exercise and effective recovery can help stem the tide on the ‘male menopause’.
If you are concerned about your hormone levels, always refer to your doctor, who will be able to explain your options when it comes to TRT or other solutions.
- Testosterone is the male-dominant sex hormone that produces anabolic and androgenic effects in the body.
- In men, testosterone production primarily occurs in the Leydig cells of the testes.
- Testosterone produces masculinising and growth-promoting effects in men, including men’s sex anatomy development and muscle mass growth.
- Testosterone plays a crucial role in male mood and behaviour and may cause increased impulsivity.
- Low male testosterone can cause side effects, such as infertility, increased body fat levels, and chronic fatigue.
- Genetics, disease, and lifestyle factors can all negatively impact sex hormone production.
- After 30, men’s testosterone levels taper off by around 1-2% each year on average, although it isn’t clear how much ageing contributes to testosterone levels.
- Healthy lifestyle habits like exercise, weight management and sleep can all positively influence men’s testosterone levels.
 Travison, T. G., et al. (2007). A population-level decline in serum testosterone levels in American men, The Journal of clinical endocrinology and metabolism, 92(1).
 Delville, Y., et al. (1996). Testosterone facilitates aggression by modulating vasopressin receptors in the hypothalamus, Physiology & Behaviour, 60(1).
 Carré, J.M., Olmstead, N.A. (2015). Social neuroendocrinology of human aggression: examining the role of competition-induced testosterone dynamics, Neuroscience, 286.
 Open Learn. (2021). How testosterone affects risk taking behaviour. https://www.open.edu/openlearn/ [Last accessed 18 August 2021].
 Open Learn. (2021). How testosterone affects risk taking behaviour.
 Men’s Health Forum. (2021). Key data: mental health. https://www.menshealthforum.org.uk/key-data-mental-health. [Last accessed 17 May 2021].
 MHFA. (2021), Mental health statistics. https://mhfaengland.org/mhfa-centre/research-and-evaluation. [Last accessed 17 May 2021].
 Rivas, A. M., et al. (2014). Diagnosing and managing low serum testosterone, Proceedings (Baylor University. Medical Center), 27(4),
 Stanworth, R. D., & Jones, T. H. (2008). Testosterone for the aging male; current evidence and recommended practice. Clinical interventions in aging, 3(1), pp. 25–44.
 Rivas, A. M., et al. (2014). Diagnosing and managing low serum testosterone.
 Emmelot-Vonk, M. H., et al. (2011). Low testosterone concentrations and the symptoms of testosterone deficiency according to the Androgen Deficiency in Ageing Males (ADAM) and Ageing Males’ Symptoms rating scale (AMS) questionnaires, Clinical endocrinology, 74(4).
 Muraleedharan, V., Jones, T. H. (2010). Testosterone and the metabolic syndrome, Therapeutic advances in endocrinology and metabolism, 1(5).
 Al Hayek, A. A., et al. (2013). Prevalence of low testosterone levels in men with type 2 diabetes mellitus: a cross-sectional study, Journal of family & community medicine, 20(3).
 Durairajanayagam, D. (2018). Lifestyle causes of male infertility, Arab Journal of Urology, 16(1).
 WebMD. (2021). Testicular Injuries: Causes and Treatments. [online] Available at: https://www.webmd.com/men/guide. [Last accessed 18 August 2021].
 Minguez-Alarcon, L. (2018). Type of underwear worn and markers of testicular function among men attending a fertility center, Human Reproduction. 33(9).
 Craig Hospital. (2021). Neuroendocrine Dysfunction in Traumatic Brain Injury: Effects of Testosterone Therapy. https://craighospital.org/programs/research. [Last accessed 18 August 2021.
 WHO. (2021). Obesity and overweight. https://www.who.int/news-room/fact-sheets. [Last accessed 12 August 2021].
 Travison, T.G, et al. (2007). A population-level decline in serum testosterone levels in American men.
 Rabasseda, X. (2012). A report from the endocrine society’s 94th annual meeting & expo (June 23-26 – Houston, Texas, USA), Drugs of today, 48(9)
 Schulz, P., et al. (1996). Lower sex hormones in men during anticipatory stress, Neuroreport. 7(18).
 Vaamonde, D., et al. (2012). Physically active men show better semen parameters and hormone values than sedentary men, European Journal of Applied Physiology, 112(9).
 Vingren, J.L., Kraemer, W.J., Ratamess et al. (2010). Testosterone physiology in resistance exercise and training: the up-stream regulatory elements. Sports Medicine. 40 (12), pp. 1037-53.
 Leproult, R., (2011). Effect of 1 Week of Sleep Restriction on Testosterone Levels in Young Healthy Men, JAMA, 305(21).
 Prasad, A. S., et al. (1996). Zinc status and serum testosterone levels of healthy adults, Nutrition, 12, (5).
 Maggio, M., et al. (2014). The Interplay between Magnesium and Testosterone in Modulating Physical Function in Men, International Journal of Endocrinology, Special Issue 2014.