Finding out that your testosterone is low can raise as many questions as it answers. The number on the blood test confirms what you suspected, that something has changed, but it does not explain why. And the why matters, because the underlying cause determines everything that follows: whether the condition is reversible, how it should be treated, and what it means for your long-term health.
Testosterone deficiency, clinically known as hypogonadism, is not a single condition with a single cause. It is an outcome that can result from a wide range of factors, some of them straightforward and modifiable, others more complex and requiring specialist input. Understanding the spectrum of causes is the first step towards getting the right diagnosis and the right care.
Two Categories of Hypogonadism: Primary and Secondary
Clinicians categorise testosterone deficiency into two broad types based on where in the hormonal system the problem originates. This distinction is not academic. It directly influences how the condition is investigated and managed.
Primary Hypogonadism
Primary hypogonadism means that the problem lies in the testes themselves. The brain is sending the correct signals to produce testosterone, but the testes are unable to respond adequately. This is sometimes called hypergonadotropic hypogonadism because the pituitary gland, sensing that testosterone is low, produces higher levels of luteinising hormone (LH) and follicle-stimulating hormone (FSH) in an attempt to stimulate the testes. Blood tests in primary hypogonadism typically show low testosterone alongside elevated LH and FSH.
Causes of primary hypogonadism include testicular injury, infections that damage the testes (such as mumps orchitis), genetic conditions, chemotherapy or radiation treatment, and undescended testes.
Secondary Hypogonadism
Secondary hypogonadism means that the testes are capable of producing testosterone, but they are not receiving the proper signals to do so. The problem lies upstream, in the hypothalamus or pituitary gland, which control testosterone production through the hormones GnRH, LH, and FSH. Blood tests in secondary hypogonadism typically show low testosterone with low or inappropriately normal LH and FSH.
Secondary hypogonadism is actually more common than primary, particularly in middle-aged and older men. Its causes include obesity, pituitary disorders, certain medications, chronic illness, and stress-related hormonal disruption.
Some men have a combination of both, which is referred to as mixed hypogonadism. This is particularly common in older men where age-related testicular decline is compounded by other factors.
Age-Related Testosterone Decline
The most common context in which men encounter falling testosterone is the natural decline associated with ageing. From approximately age 30, testosterone levels decrease by roughly 1% to 2% per year. This is a normal physiological process and reflects gradual changes in both testicular function and the hypothalamic-pituitary axis that regulates testosterone production.
However, the rate of decline varies enormously between individuals. Some men maintain robust testosterone levels well into their 70s and beyond. Others experience a more pronounced decline that brings their levels into the deficient range by their late 40s or early 50s. The difference is influenced by genetics, body composition, overall health, and lifestyle factors.
It is important to distinguish between the normal, gradual decline that most men experience and late-onset hypogonadism, where levels fall low enough to produce clinically significant symptoms. The former is a fact of biology. The latter is a medical condition that warrants assessment and may benefit from treatment. The NHS recognises this distinction, though in practice the line between the two is not always clearly drawn in primary care.
Obesity and Excess Body Fat
Obesity is one of the most significant and most modifiable causes of low testosterone in men. The relationship is powerful, bidirectional, and well-supported by evidence.
Adipose tissue, particularly visceral fat around the abdomen, contains an enzyme called aromatase that converts testosterone to oestradiol, a form of oestrogen. The more body fat a man carries, the more active this conversion becomes, and the more testosterone is effectively removed from circulation. At the same time, excess oestrogen feeds back to the hypothalamus and pituitary gland, suppressing the signals that drive testosterone production. The result is a self-reinforcing cycle: more fat leads to less testosterone, which leads to further fat gain, which leads to even less testosterone.
Studies have consistently shown that obese men have significantly lower testosterone levels than men of healthy weight, and that weight loss can meaningfully increase testosterone levels in many cases. A landmark study published in the Journal of Clinical Endocrinology & Metabolism demonstrated that substantial weight loss through lifestyle modification can raise testosterone levels by several nmol/L in obese men with deficiency.
This does not mean that weight loss alone will resolve testosterone deficiency in every case, particularly where other causes are also present. But it does mean that body composition is a critically important factor in any assessment of low testosterone.
Chronic Illness and Medical Conditions
A number of chronic medical conditions are associated with low testosterone, either through direct effects on the testes, disruption of the hypothalamic-pituitary axis, or systemic inflammation that suppresses hormonal function.
Type 2 diabetes is strongly associated with low testosterone. The relationship is bidirectional: insulin resistance promotes testosterone decline, and testosterone deficiency worsens insulin resistance. Men with type 2 diabetes are significantly more likely to have low testosterone than men without the condition.
Chronic kidney disease can affect testosterone production through multiple mechanisms, including altered gonadotropin metabolism and increased inflammation. Men on dialysis are particularly likely to have low testosterone levels.
Liver disease, particularly cirrhosis, disrupts testosterone production and increases the level of sex hormone-binding globulin (SHBG), which reduces the amount of free, biologically active testosterone available to the body.
HIV/AIDS is associated with hypogonadism through both the disease process itself and some of the medications used to treat it.
Chronic obstructive pulmonary disease (COPD) and other chronic respiratory conditions are associated with lower testosterone levels, likely due to a combination of systemic inflammation, reduced physical activity, and corticosteroid use.
Obstructive sleep apnoea is a significant and underappreciated cause of low testosterone. Testosterone production is closely linked to sleep quality, and the repeated oxygen desaturations and sleep fragmentation caused by sleep apnoea can substantially suppress testosterone levels. Treating sleep apnoea with CPAP therapy has been shown to improve testosterone levels in some men.
Medications That Can Lower Testosterone
Several classes of medication can suppress testosterone production, sometimes significantly. If you are taking any of the following and experiencing symptoms of low testosterone, it is worth discussing this with your clinician.
Opioid pain medications are among the most common pharmaceutical causes of low testosterone. Both short-acting and long-acting opioids suppress the hypothalamic-pituitary-gonadal axis, and the effect can be substantial. Studies have found that up to 90% of men on long-term opioid therapy have testosterone levels below the normal range. This condition is known as opioid-induced androgen deficiency (OPIAD) and is increasingly recognised as a significant clinical problem.
Glucocorticoids (corticosteroids such as prednisolone and dexamethasone) suppress testosterone production through effects on both the pituitary gland and the testes. Men on long-term corticosteroid therapy are at increased risk of hypogonadism.
Anabolic steroids, paradoxically, are a major cause of low testosterone. When exogenous testosterone or other anabolic steroids are used, the body’s natural production shuts down. After stopping steroid use, it can take months or even years for natural production to recover, and in some cases, it does not fully recover at all. This is a particularly common problem in men who have used steroids for bodybuilding or performance enhancement.
Certain antidepressants and antipsychotics can affect testosterone levels, though the mechanisms vary by medication. Some antipsychotics increase prolactin levels, which in turn suppresses testosterone production.
5-alpha reductase inhibitors (finasteride, dutasteride), used for hair loss and benign prostatic hyperplasia, do not lower total testosterone but alter the hormonal environment in ways that can produce symptoms similar to low testosterone in some men.
Stress, Cortisol, and the Hormonal Balance
Chronic psychological stress has a measurable effect on testosterone levels. The mechanism involves cortisol, the body’s primary stress hormone. Cortisol and testosterone have an inverse relationship: when cortisol is chronically elevated, testosterone production is suppressed.
This is not a trivial effect. Prolonged periods of high stress, whether from work pressure, financial worry, relationship difficulties, or other sources, can meaningfully lower testosterone levels. The hypothalamus responds to sustained cortisol elevation by reducing GnRH output, which in turn reduces LH secretion and testosterone production.
Men across the UK, from high-pressure roles in the City of London to demanding jobs in Belfast, Edinburgh, or Cardiff, may be experiencing stress-related testosterone suppression without realising that the two are connected. The symptoms of chronic stress and the symptoms of low testosterone overlap considerably, which can make it difficult to identify which is driving the other, or whether both are operating simultaneously.
Addressing chronic stress is important for hormonal health, but it is also important to recognise that stress reduction alone may not restore testosterone levels if other factors are contributing to the deficiency.
Sleep Deprivation
Testosterone production follows a circadian rhythm, with the majority of daily testosterone release occurring during sleep, particularly during the deeper stages of sleep. This is why testosterone levels are highest in the morning and why blood tests are ideally performed early in the day.
When sleep is consistently insufficient or poor quality, testosterone production drops correspondingly. A well-known study demonstrated that restricting healthy young men to five hours of sleep per night for one week reduced their testosterone levels by 10% to 15%. In men who are already in the lower end of the reference range, this kind of reduction can push levels into the deficient zone.
Chronic sleep deprivation is endemic in modern life, and its effects on testosterone are often underappreciated. Poor sleep may be both a cause and a consequence of low testosterone, since testosterone deficiency itself is associated with sleep disturbance, creating another self-reinforcing cycle.
Pituitary Gland Disorders
The pituitary gland, sometimes called the master gland, sits at the base of the brain and controls testosterone production by releasing LH and FSH. Conditions that affect the pituitary can disrupt this signalling and cause secondary hypogonadism.
Pituitary adenomas (benign tumours) are the most common pituitary disorder affecting testosterone. Even small, non-functional adenomas can compress the surrounding tissue and impair hormone production. Prolactinomas, which secrete excess prolactin, are particularly likely to suppress testosterone.
Hemochromatosis, a genetic condition causing iron overload, can damage the pituitary gland and is an important but often overlooked cause of secondary hypogonadism. It is more common in men of Northern European descent and is particularly prevalent in Ireland and the UK.
Head trauma can damage the pituitary gland or hypothalamus, leading to hormonal deficiencies that may not become apparent until months or years after the injury. This is increasingly recognised in contact sports and in veterans who have experienced blast injuries.
Radiation therapy to the head or brain, as used in the treatment of certain cancers, can damage the pituitary and cause permanent hormonal deficiency.
Testicular Injury and Conditions
Direct damage to the testes is a cause of primary hypogonadism. This can result from physical trauma, torsion (twisting of the testicle that cuts off blood supply), or surgical complications. The extent of the impact on testosterone production depends on the severity of the injury and whether one or both testes are affected.
Mumps orchitis, an inflammation of the testes caused by the mumps virus, can permanently damage testosterone-producing cells if it occurs after puberty. While vaccination has made this less common, it still occurs and can have lasting effects on hormonal function.
Undescended testes (cryptorchidism) that are not corrected in early childhood can lead to impaired testosterone production later in life, as the higher temperature of the abdominal cavity damages the testicular tissue over time.
Varicocele, an enlargement of the veins within the scrotum, can affect testicular function and testosterone production in some men, though the relationship is not straightforward and not all varicoceles cause hormonal problems.
Genetic Conditions
Klinefelter syndrome is the most common genetic cause of primary hypogonadism in men. It occurs when a male is born with an extra X chromosome (47,XXY instead of 46,XY). It affects approximately 1 in 660 men, though many cases are not diagnosed until adulthood when fertility problems or symptoms of low testosterone prompt investigation. Men with Klinefelter syndrome typically have small, firm testes, reduced testosterone production, and impaired fertility.
Kallmann syndrome is a rare genetic condition that affects the development of the hypothalamus and is associated with delayed or absent puberty and an impaired sense of smell. It causes secondary hypogonadism because the hypothalamus fails to produce adequate GnRH.
Other rare genetic conditions affecting testosterone production exist, but Klinefelter and Kallmann syndromes are the most commonly encountered in clinical practice.
Lifestyle Factors
Beyond the major causes discussed above, several lifestyle factors can contribute to lower testosterone levels.
Excessive alcohol consumption suppresses testosterone through multiple mechanisms, including direct toxicity to the testes, increased aromatase activity, and disruption of the hypothalamic-pituitary axis. Heavy drinking is a well-established cause of hypogonadism.
Sedentary lifestyle is associated with lower testosterone, while regular physical activity, particularly resistance training, is associated with higher levels. The relationship is likely mediated through the effects of exercise on body composition, insulin sensitivity, and stress hormones.
Poor diet, particularly one that is excessively restrictive or very low in fat, can affect testosterone production. Testosterone is synthesised from cholesterol, and extremely low-fat diets can theoretically reduce substrate availability. More practically, diets that promote obesity or metabolic dysfunction will affect testosterone through the mechanisms described earlier.
Environmental endocrine disruptors, such as certain pesticides, plasticisers (BPA), and industrial chemicals, have been shown to interfere with hormone production and function in laboratory studies. The extent to which typical environmental exposures affect testosterone levels in men remains an active area of research, but there is growing concern about the cumulative impact of these substances.
Why Identifying the Cause Matters
Understanding the cause of your low testosterone is not just intellectually satisfying. It directly affects your treatment plan and long-term outlook. A man whose testosterone is low because of obesity may benefit most from a weight management programme, potentially alongside testosterone therapy. A man with a pituitary adenoma needs imaging and possibly neurosurgical assessment. A man whose testosterone has been suppressed by opioid medication may see improvement if pain management can be achieved through alternative means.
Proper investigation typically involves a comprehensive blood panel, not just total testosterone but also LH, FSH, prolactin, SHBG, thyroid function, and sometimes additional markers depending on clinical suspicion. This is the kind of thorough assessment that a specialist service is well-placed to provide.
At Evernu, our RQIA-regulated clinicians take a comprehensive approach to diagnosing and managing testosterone deficiency. We investigate the underlying cause, not just the number, because effective treatment depends on understanding the full picture. Whether you are in Northern Ireland, England, Scotland, or Wales, we provide accessible, evidence-based care that treats you as an individual, not a lab result.
If you are experiencing symptoms that might be related to low testosterone, start your assessment today and let us help you understand what is happening and what can be done about it.
Frequently Asked Questions About the Causes of Low Testosterone
Can stress really cause low testosterone?
Yes, chronic psychological stress can measurably suppress testosterone production. Cortisol, the body’s primary stress hormone, has an inverse relationship with testosterone. When cortisol is chronically elevated due to sustained stress, the hypothalamus reduces its output of GnRH, which reduces LH secretion and consequently testosterone production. While acute, short-term stress is unlikely to have a lasting effect, prolonged stress over weeks, months, or years can meaningfully lower testosterone levels.
Can low testosterone be caused by previous steroid use?
Yes, this is a well-recognised cause. When exogenous testosterone or anabolic steroids are used, the body’s natural testosterone production shuts down because the hypothalamic-pituitary axis detects adequate (or excessive) hormone levels and stops sending production signals. After steroid use is discontinued, natural production can take months or years to recover, and in some cases, particularly after prolonged or high-dose use, it may not fully recover without medical intervention.
Does poor sleep lower testosterone?
Yes, sleep is directly linked to testosterone production. The majority of daily testosterone secretion occurs during sleep, particularly during the deeper stages. Studies have shown that restricting sleep to five hours per night for just one week can reduce testosterone levels by 10% to 15% in healthy young men. Chronic sleep deprivation, which is common in modern life, can contribute significantly to testosterone deficiency over time. Conditions like obstructive sleep apnoea, which fragment sleep and cause repeated oxygen desaturations, are also strongly associated with low testosterone.
Is low testosterone always permanent?
No. The reversibility of low testosterone depends entirely on the cause. Low testosterone caused by obesity, medication, stress, or sleep deprivation may improve or resolve when the underlying cause is addressed. Low testosterone caused by genetic conditions, testicular damage, or pituitary destruction is typically permanent and requires ongoing management. In cases where the cause is age-related decline compounded by lifestyle factors, a combination of lifestyle modification and medical treatment may be appropriate. This is why identifying the underlying cause is so important.
Can being overweight cause low testosterone even in younger men?
Absolutely. The relationship between obesity and low testosterone is not age-dependent. Younger men with significant excess body fat can have testosterone levels well below the normal range due to increased aromatase activity (conversion of testosterone to oestrogen in fat tissue) and the resulting suppression of the hypothalamic-pituitary axis. In fact, some studies suggest that obesity is an even more significant predictor of low testosterone than age in men under 50. Weight loss can substantially improve testosterone levels in these cases, though additional investigation is warranted to ensure that other causes are not also present.
