"As you get older, your testosterone levels inevitably decrease."
This assumption is widespread. However, a closer look at the scientific evidence shows that this relationship is much more nuanced. While lower levels are measured on average in older men, the decline cannot be explained by chronological age alone.
In addition to age, metabolic and lifestyle factors primarily influence testosterone regulation. These include body fat percentage, sleep duration, physical activity, stress levels, and cardiometabolic diseases. Several studies have shown that these factors often have a greater influence on testosterone levels than age itself (Kelly & Jones, 2015; Grossmann, 2011).
In fact, clinical observations show that many men can have stable or even relatively high testosterone levels even in older age, especially if they are metabolically healthy and maintain an active lifestyle (Feldman et al., 2002).
The following article highlights two important developments: changes in testosterone levels over the course of life, and the observed decline in average testosterone levels across generations. It also explains the role of lifestyle factors and when medical clarification may be advisable.
Testosterone over the course of life
Testosterone production primarily occurs in the Leydig cells of the testes and is regulated by the hypothalamic-pituitary-gonadal axis. Specifically, luteinizing hormone (LH) stimulates the testes to produce testosterone.
Population-based cohort studies often show an average decline in total testosterone of about 1 to 2 percent per year starting from the third decade of life (Jones & Stanworth, 2008). However, it is important to note that this average value exhibits considerable interindividual variation and is strongly influenced by cofactors.
Several physiological changes can occur over the course of life:
Changes in Leydig Cell Function
With increasing age, the steroidogenic activity of Leydig cells can decrease. At the same time, studies show reduced sensitivity to luteinizing hormone, which can further limit testosterone production (Wu et al., 2010).
Changes in hormonal regulation
Regulation via the hypothalamic-pituitary-gonadal axis can also change. Adjustments in GnRH and LH secretion can occur, which influence testosterone production (Veldhuis et al., 2008).
Increase in SHBG
Parallel to age, the concentration of sex hormone-binding globulin (SHBG) often increases. This reduces the proportion of free, biologically active testosterone, even if total testosterone only moderately decreases (Feldman et al., 2002).
The following graph shows, by way of example, the average testosterone levels across different age groups.
These values represent statistical averages. Individually, testosterone levels can remain stable even in older age, especially with good metabolic health and an active lifestyle.
Low testosterone levels can be associated with a variety of non-specific symptoms. These include, among others:
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reduced physical performance (Bhasin et al., 2001)
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decrease in muscle mass (Bhasin et al., 1997)
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increase in visceral adipose tissue (Kelly & Jones, 2015)
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persistent fatigue (Wang et al., 1996)
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mood swings (Zarrouf et al., 2009)
It is crucial that these isolated symptoms are not diagnostic and must always be assessed in the overall clinical picture.
You can find more about causes, symptoms, and possible connections in our article " Testosterone Deficiency in Men: Causes, Symptoms, and Solutions".
Declining testosterone levels across generations
In addition to age-dependent changes, there is evidence of an additional, cross-generational trend. Men of the same age today have, on average, lower testosterone levels than earlier comparison cohorts.
This effect was described, among others, in the Massachusetts Male Aging Study (MMAS), which showed that men of the same age in later study years had lower testosterone levels than men of the same age groups in earlier decades (Travison et al., 2007). This trend was later confirmed in further analyses (Perheentupa et al., 2012).
This finding suggests that in addition to individual factors, societal or environmental changes may also play a role. The discussion includes influences from so-called endocrine disruptors, i.e., hormonally active environmental chemicals that can be found in plastics, pesticides, or cosmetics (Hauser et al., 2015).
The following graphic illustrates this observed generational decline.
Parallel to this development, several societal factors have also changed, which have been shown to influence hormonal regulation.
These include, among others:
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increasing prevalence of obesity and metabolic syndrome (Corona et al., 2010)
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increasing physical inactivity (Hayes et al., 2015)
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chronic sleep deprivation (Leproult & Van Cauter, 2011)
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increasing psychosocial stress load (Chrousos, 2009)
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possible effects of certain environmental chemicals (Diamanti-Kandarakis et al., 2009)
The causes are probably multifactorial. However, it is clear that testosterone levels are closely related to general metabolic health and lifestyle.
Lifestyle factors as a central lever
Even though genetic factors play a role, hormone balance is strongly influenced by everyday habits.
Several lifestyle factors have a measurable impact on testosterone regulation.
Body weight and metabolism
Obesity is one of the most important modifiable risk factors for low testosterone levels. Visceral adipose tissue, in particular, plays a central role in hormonal balance. It exhibits increased aromatase activity, which leads to increased conversion of testosterone into estradiol.
At the same time, estradiol in men acts as a significant negative feedback regulator of the hypothalamic-pituitary-gonadal axis and can additionally inhibit endogenous testosterone production (Cooke et al., 2017; Finkelstein et al., 2013).
Visceral fat can therefore influence testosterone production on two levels: firstly, through increased conversion of testosterone into estradiol, and secondly, through increased negative feedback via estradiol on the hormonal regulation of testicular function.
Studies also show that weight reduction in overweight men is often accompanied by a measurable increase in testosterone levels (Kelly & Jones, 2015).
Strength training and physical activity
Regular physical activity, especially strength training and high-intensity exercise, can lead to a short-term increase in testosterone levels and also have a positive long-term effect through metabolic adaptations (Kraemer & Ratamess, 2005; Hayes et al., 2015).
These include improvements in insulin sensitivity, a reduction in fat mass, and the preservation or build-up of muscle mass.
These changes can in turn have positive effects on the regulation of the hypothalamic-pituitary-gonadal axis and thus contribute to more stable testosterone levels in the long term (Vingren et al., 2010).
Find out more about how testosterone, metabolic health, and long-term quality of life are closely related in our article " Testosterone and Longevity: How Hormone Levels Affect Our Quality of Life".
Sleep quality
A significant portion of testosterone secretion occurs during nocturnal sleep phases. Even short-term sleep deprivation can lead to measurable reductions in testosterone levels (Leproult & Van Cauter, 2011).
Sleep deprivation also negatively affects several hormonal systems, including cortisol and insulin sensitivity.
Stress management
Chronic psychosocial stress permanently activates the hypothalamic-pituitary-adrenal axis and leads to elevated cortisol levels. Cortisol can inhibit the function of the HPG axis, thereby reducing testosterone production. Studies show that elevated cortisol levels can directly suppress testosterone secretion (Cumming et al., 1983).
In the long term, chronic activation of the stress axis can therefore contribute to a decrease in testosterone levels (Chrousos, 2009).
Nutrition
Diet also plays an important role in hormonal regulation. A balanced diet with adequate energy intake, high-quality proteins, healthy fats, and micronutrients supports hormonal balance.
Energy availability also plays a central role. A persistently reduced caloric intake can lower testosterone production, especially if accompanied by rapid weight loss or very low fat intake (Volek et al., 1997; Areta et al., 2020).
In addition, a connection between micronutrient status, especially zinc (Prasad et al., 1996) and vitamin D, and testosterone regulation is discussed (Pilz et al., 2010).
You can find more about the influence of vitamin D on testosterone levels in our article "Vitamin D – How the sunshine vitamin influences testosterone levels".
When a hormonal evaluation is advisable
Not every fatigue or decrease in performance automatically indicates testosterone deficiency. However, if several typical symptoms persist for a longer period, a structured hormonal diagnosis may be useful.
Typical initiating symptoms include, for example:
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Chronic fatigue
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Reduced physical performance
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Difficulties in building muscle
Laboratory diagnostic clarification should be standardized and usually includes:
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Albumin
Blood samples should be taken in the morning, ideally between 8 and 11 am, as testosterone is subject to significant daily fluctuations and typically shows its highest values in the early morning hours (Diver et al., 2003).
The interpretation of the values should always be made by a doctor within the clinical context.
Testosterone therapy: When it can be useful
If a clinically relevant hypogonadism is present, medically supervised testosterone replacement therapy can be an effective treatment option.
The current guidelines of the European Association of Urology (EAU) recommend testosterone therapy for men with typical symptoms and at least two documented low serum testosterone levels. Generally, a total testosterone level below approximately 12.1 nmol/L (≈ 350 ng/dL) in combination with corresponding symptoms is considered a clinical threshold or a possible indication of hypogonadism requiring treatment (EAU Guidelines on Sexual and Reproductive Health).
Before starting therapy, a structured diagnosis should therefore be performed. This includes at least two morning testosterone measurements and further hormonal evaluation of pituitary hormones to differentiate between primary and secondary causes of hypogonadism.
The goal of therapy is to restore testosterone levels to a physiological range, thereby improving symptoms.
Possible effects of a correctly indicated therapy can include:
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Improvement in energy and physical performance
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Increase in muscle mass
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Reduction of fat mass
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Improvement of libido and sexual function
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Mood stabilization
However, the therapy should always be individually planned and medically supervised. Regular check-ups are necessary to ensure safety and effectiveness. This includes, in particular, monitoring testosterone levels, hematocrit, PSA, and clinical symptoms.
It is important to note: Testosterone therapy is not a substitute for a healthy lifestyle. It is not a lifestyle medication, but a medical treatment for men with diagnosed hypogonadism.
Conclusion: Why age is not the only factor
Testosterone changes throughout life are a complex interplay of biological age, lifestyle, and metabolic health. In many cases, hormonal changes can be positively influenced by targeted adjustments in exercise, nutrition, sleep, and stress management.
In the case of persistent complaints and corresponding findings, a structured medical evaluation and, if necessary, therapy may be advisable.
