“With increasing age, testosterone levels inevitably decline.”
This assumption is widespread. However, a closer look at the scientific evidence shows that this relationship is far 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, as well as cardiometabolic diseases. Several studies have shown that these factors often have a greater impact on testosterone levels than age itself (Kelly & Jones, 2015; Grossmann, 2011).
In fact, clinical observations show that many men can maintain stable or even relatively high testosterone levels even in their later years, 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 evaluation may be advisable.
Testosterone over the course of life
Testosterone is primarily produced in the Leydig cells of the testes and is regulated via the so-called hypothalamus-pituitary-gonadal axis. 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 in the third decade of life (Jones & Stanworth, 2008). However, it is important to note that this average value shows considerable interindividual variation and is strongly influenced by accompanying factors.
Several physiological changes can occur over the course of life:
Changes in Leydig cell function
With increasing age, the steroidogenic activity of Leydig cells may decline. Studies also show reduced sensitivity to luteinizing hormone, which can further limit testosterone production (Wu et al., 2010).
Changes in hormonal regulation
Regulation via the hypothalamus-pituitary-gonadal axis can also change. Adjustments in GnRH and LH secretion may occur, affecting testosterone production (Veldhuis et al., 2008).
Increase in SHBG
Parallel to aging, the concentration of sex hormone-binding globulin (SHBG) increases in many cases. This reduces the proportion of freely available, biologically active testosterone, even if total testosterone only moderately declines (Feldman et al., 2002).
The following chart illustrates the average testosterone levels across different age groups.
These values represent statistical averages. Individual testosterone levels can remain stable even in later years, especially with good metabolic health and an active lifestyle.
Low testosterone levels can be associated with a variety of non-specific symptoms. These include:
-
reduced physical performance (Bhasin et al., 2001)
-
loss of muscle mass (Bhasin et al., 1997)
-
increase in visceral fat (Kelly & Jones, 2015)
-
persistent fatigue (Wang et al., 1996)
-
mood swings (Zarrouf et al., 2009)
Crucially, these symptoms occur in isolation, are not diagnostic, and must always be assessed in the overall context.
You can find out 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-related changes, there is evidence of a further trend across generations. Men of the same age today have lower average 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 had lower testosterone levels in later years of the study than men in 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 influence of so-called endocrine disruptors, i.e., environmentally occurring chemicals with hormonal effects that can be found in plastics, pesticides, or cosmetics, is also being discussed (Hauser et al., 2015).
The following chart illustrates this observed generational decline.
Parallel to this development, several societal factors have also changed that have been shown to influence hormonal regulation.
These include, among others:
-
the rising prevalence of obesity and metabolic syndrome (Corona et al., 2010)
-
increasing physical inactivity (Hayes et al., 2015)
-
chronic sleep deprivation (Leproult & Van Cauter, 2011)
-
rising psychosocial stress (Chrousos, 2009)
-
the possible effects of certain environmental chemicals (Diamanti-Kandarakis et al., 2009)
The causes are likely multifactorial. However, it is clear that testosterone levels are closely linked to overall metabolic health and lifestyle.
Lifestyle factors as a key lever
Although genetic factors play a role, the hormone balance is strongly influenced by everyday habits.
Several lifestyle factors have a measurable impact on testosterone regulation.
Body weight and metabolism
Overweight is one of the most important modifiable risk factors for low testosterone levels. Visceral fat tissue, in particular, plays a central role in hormonal balance. It has increased aromatase activity, which causes testosterone to be converted more frequently into estradiol.
At the same time, estradiol acts as a major negative feedback regulator of the hypothalamus-pituitary-gonadal axis in men and can further inhibit endogenous testosterone production (Cooke et al., 2017; Finkelstein et al., 2013).
Visceral fat can thus influence testosterone production on two levels: on the one hand, through increased conversion of testosterone into estradiol, and on the other hand, through increased negative feedback of estradiol on the hormonal regulation of testicular function.
Studies also show that weight loss in overweight men is often associated with 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).
This includes, among others, improvements in insulin sensitivity, a reduction in body fat, as well as the maintenance or building of muscle mass.
These changes can, in turn, have positive effects on the regulation of the hypothalamus-pituitary-gonadal axis and thus contribute to more stable testosterone levels in the long term (Vingren et al., 2010).
You can find out how closely testosterone, metabolic health, and long-term quality of life are linked in our article “Testosterone and Longevity: How Hormone Levels Influence Our Quality of Life.”
Sleep quality
A major part of testosterone secretion occurs during the nighttime sleep phases. Even short-term sleep deprivation can lead to measurable reductions in testosterone levels (Leproult & Van Cauter, 2011).
Sleep deprivation also has a negative effect on several hormonal systems, including cortisol and insulin sensitivity.
Stress management
Chronic psychosocial stress persistently activates the hypothalamic-pituitary-adrenal axis and leads to elevated cortisol levels. Cortisol can inhibit the function of the HPG axis and thus reduce 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 lower testosterone levels (Chrousos, 2009).
Nutrition
Nutrition also plays an important role in hormonal regulation. A balanced diet with sufficient energy intake, high-quality proteins, healthy fats, and micronutrients supports hormonal balance.
Energy availability also plays a central role. Persistently reduced calorie intake can lower testosterone production, especially when accompanied by rapid weight loss or very low fat intake (Volek et al., 1997; Areta et al., 2020).
In addition, a link between micronutrient status, especially zinc (Prasad et al., 1996) and vitamin D, and testosterone regulation is discussed (Pilz et al., 2010).
You can find out more about the effect of vitamin D on testosterone levels in our article “Vitamin D – How the sunshine vitamin affects testosterone levels”.
When a hormonal assessment makes sense
Not every instance of fatigue or reduced performance is automatically a testosterone deficiency. However, if several typical symptoms occur over a longer period, a structured hormonal assessment may be useful.
Typical symptoms include, for example:
-
chronic fatigue
-
reduced physical performance
-
difficulty building muscle
Laboratory-based assessment should be standardized and usually includes:
-
Albumin
The blood sample should be taken in the morning, ideally between 8 a.m. and 11 a.m., because testosterone is subject to pronounced diurnal fluctuations and typically reaches its highest levels in the early morning hours (Diver et al., 2003).
The results should always be interpreted in a clinical context by a doctor.
Testosterone therapy: When it may be useful
If clinically relevant hypogonadism is present, doctor-supervised testosterone replacement therapy can be an effective treatment option.
Current guidelines from the European Association of Urology (EAU) recommend testosterone therapy for men with typical symptoms and serum testosterone levels that have been found to be low on at least two occasions. A total testosterone level below approximately 12.1 nmol/L (≈ 350 ng/dL), in combination with corresponding symptoms, is generally considered a clinical threshold or a possible indication of hypogonadism requiring treatment (EAU Guidelines on Sexual and Reproductive Health).
A structured assessment should therefore be carried out before starting therapy. This should include at least two morning testosterone measurements as well as further hormonal assessment of pituitary hormones to distinguish between primary and secondary causes of hypogonadism.
The goal of therapy is to bring the testosterone level back into a physiological range and thus improve the symptoms.
Possible effects of a correctly indicated therapy include:
-
Improved energy and physical performance
-
Increased muscle mass
-
Reduced body fat
-
Improved libido and sexual function
-
Stabilized mood
However, therapy should always be individually planned and medically supervised. Regular check-ups are necessary to ensure safety and effectiveness. These should include monitoring testosterone levels, hematocrit, PSA, as well as clinical symptoms.
It is important to note: testosterone therapy does not replace a healthy lifestyle. It is not a lifestyle medication, but a medical treatment for men diagnosed with hypogonadism.
Conclusion: Why age is not the only factor
Changes in testosterone levels over the course of life are a complex interplay of biological age, lifestyle, and metabolic health. In many cases, hormonal changes can be positively influenced through targeted adjustments in exercise, nutrition, sleep, and stress management.
In cases of persistent symptoms and corresponding findings, a structured medical assessment and, if necessary, therapy may be useful.
