Testosterone levels in men are decreasing globally at an alarming rate. Recent studies show a steady and significant decline of 1% per year since the 1970s (1). Most concerning is the reduction in adolescent and young adult males, who have experienced a 25% drop between 1999 and 2016 (2). This decline appears to have been particularly rapid in the last two decades. The result is that modern men now have testosterone levels that are 20–30% lower than those of their fathers’ generation (1). This is a serious public health issue, as low testosterone is associated with a range of health problems. These include:
- Reduced bone density
- Loss of muscle mass and strength
- Decline in libido, fertility and sexual function
- Mood disturbance
- Poor cognitive function
- Increased risk of dementia, obesity, and metabolic and cardiovascular disease (3).
So, what’s causing testosterone decline? We’ll explore the potential causes of this concerning phenomenon and provide evidence-based strategies to help mitigate it.
How much testosterone should we have?
In adult males, normal total testosterone concentrations typically fall within the range of 10–35 nmol/L (300–1000 ng/dL) (4). Levels below 10.4 nmol/L, particularly when accompanied by clinical symptoms, are classified as hypogonadism. This condition reflects inadequate testosterone production by the testes and is estimated to affect up to 40% of men aged 45 years and older (2).
The most common way to check testosterone levels is with a blood test. This test usually measures both total and free testosterone. Total testosterone is the amount of the hormone in your bloodstream. It includes bound testosterone, which is the portion bound to proteins, mainly sex hormone-binding globulin (SHBG), and free testosterone, which is unbound and active. Free testosterone makes up about 1–4% of the total. Because it’s not attached to proteins, it can quickly enter cells and produce effects, such as helping stimulate muscle protein growth.
Symptoms of low testosterone
There are symptoms that can indicate low testosterone levels, which include:
- A decrease in body hair
- A decrease in haemoglobin and mild anaemia
- Breast development (gynecomastia)
- Decreased sense of well-being
- Depressed mood
- Difficulties with concentration and memory
- Erectile dysfunction
- Fatigue
- Increased body fat
- Infertility
- Loss of muscle mass and strength
- Low sex drive
- Moodiness and irritability
- Osteoporosis (thinning of the bones)
While these symptoms can be an indicator of low testosterone, they may also be symptoms of other medical conditions. That’s why it’s important to visit a qualified healthcare professional to give you an accurate diagnosis.
Causes of low testosterone
Low testosterone levels can be caused by a number of factors. These include existing health conditions, certain medications, exposure to endocrine-disrupting chemicals, unhealthy body composition, ageing, and various lifestyle habits.
Some of the most common medical causes are type 2 diabetes, metabolic syndrome, obesity, pituitary gland disorders, testicular conditions, chronic illnesses such as kidney or liver disease, thyroid disorders, and sleep apnoea.
In other cases, low testosterone is not caused by the medical condition itself but by the treatments used to manage it. Long-term use of opioids, glucocorticoids, and some chemotherapy or radiation therapies can all suppress testosterone production.
The dangers of endocrine-disrupting chemicals
Endocrine-disrupting chemicals (EDCs) are natural or man-made substances that block, mimic, or alter hormones. They can bind to hormone receptors, change hormone production, or interfere with hormone transport and metabolism.
Several have been shown to reduce testosterone levels. For example, Bisphenol A (BPA) found in plastics and the lining of food tins, mimics oestrogen and reduces testosterone synthesis. Phthalates (e.g., DEHP, DBP), which occur in plastics and personal care products, block androgen receptors and lower testosterone.
How body composition affects testosterone
There is a well-acknowledged correlation between testosterone and body composition. Males with greater muscle mass typically have higher testosterone, while those with greater fat mass tend to exhibit lower levels. This is because excess body fat, particularly abdominal fat, is associated with an increase in activity of the enzyme aromatase, which converts testosterone to oestrogen, thereby reducing testosterone levels (5).
Ageing
In males, testosterone levels typically peak in the late teens or early 20s. Then, around 30 to 40 years old, there tends to be a decline of approximately 1-2% per year. However, this decline may not be as inevitable as previously thought. The results of a study by Sartorius et al., (5) found no decrease in testosterone associated with age among men over 40 years who were in very good or excellent health. Based on these findings, the authors suggest that the decline in testosterone often seen in older men with non specific symptoms is more likely due to age related health conditions than to a true testosterone deficiency.
The impact of lifestyle
Aspects of our lifestyle, including physical activity, sleep, chronic stress, diet, and alcohol and substance abuse, have been shown to negatively impact testosterone levels. For example, reducing sleep to five hours per night for only one week resulted in a decrease of 10-15% in healthy young men (6). While just six weeks of moderate alcohol consumption, equivalent to half a bottle of wine or two cans of lager per day, reduced testosterone levels by 6.8% (7).
Chronic stress can be particularly detrimental to maintaining healthy testosterone levels, with reductions of 20-40% being reported. This is primarily due to an elevation of the stress hormone cortisol, which suppresses the release of testosterone at various stages of production (8).
Physical activity generally has a beneficial effect on testosterone, as the most active individuals tend to have higher levels than the least active (9). However, it’s important to avoid excessive exercise and overtraining as this is strongly associated with a reduction in testosterone (10).
We are what we eat
A diverse range of foods and ingredients have been shown to negatively impact testosterone levels. These include: mint, liquorice, vegetable oils, flaxseed, processed foods, and peanuts, walnuts, and almonds. For example, the consumption of just 7 grams of liquorice root per day for 1 week has been shown to reduce testosterone levels by 26% (11).
Arguably, the most controversial food when it comes to testosterone is soy. One study (12) showed that the consumption of 56 g of pure soy protein powder per day for a period of 4 weeks was associated with a 19% decrease in testosterone. However, findings have not been consistent across all studies. A meta-analysis by Hamilton-Reeves et al., (13) found that the consumption of soy foods did not alter testosterone levels.
It’s not only specific foods that influence testosterone levels, but also the quantity of certain macronutrients in the diet. For example, low-carb diets (≤35% of calories from carbohydrate) have been shown to reduce total testosterone and increase cortisol (14).
Similarly, low fat diets (<20% calories from fat) are consistently associated with lower testosterone. While moderate fat diets (30–40% calories from fat) tend to support higher testosterone levels (15).
Poor micronutrient intake can impact testosterone levels and is increasingly common. The typical Western diet lacks a number of key vitamins and minerals, which play a direct role in testosterone production, regulation, and signalling. These include vitamin D, magnesium, zinc, vitamin B12, vitamin K2, Iodine, and selenium.
Moving forward: What we can do about declining testosterone
Testosterone levels in men are dropping around the world, and this has serious effects on health. While there is no single cause, many contributing factors have been identified. These include poor lifestyle habits, more chronic diseases, exposure to certain chemicals, and changes in diet and body composition. The good news is that many of these causes can be improved.
Knowing the signs and causes of low testosterone is the first step. The next step is taking action. In part two of this series, we’ll look at simple, evidence-based strategies that men and health professionals can use to support healthy testosterone levels. These include better sleep, good nutrition, regular exercise, lowering stress, and reducing exposure to harmful chemicals.
The decline in testosterone is worrying, but it is not something we have to accept. With the right choices and habits, men can protect—and even improve—their hormone health.
References
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