Why are men's testosterone levels declining?

Odds are your granddad probably had higher testosterone levels than you – but why?

For decades, testosterone levels have been dropping from one generation to the next [1]. In other words, your testosterone levels are probably less than your granddad’s were at your age. And it looks like the trend could be accelerating [2].

It’s not just testosterone either. Sperm counts have halved over the last 45 years [3].

So, what’s going on?

We look at the most likely culprits and what you can do about it.

In this article, we cover:

• The generational decline in testosterone
• Why are testosterone levels falling?
• How important is testosterone for men?
• Should we be worried?
• Measuring testosterone levels
   

The generational decline in testosterone

Let’s rewind to the 60s. According to one study, the average testosterone level of a man in his 30s at this time was around 23.8 nmol/L. Fast-forward to a man of the same age today, and it’s closer to 17.1 nmol/L.

That’s a drop of around 28%.

When you factor in differing lab methods and other artifacts, we’re likely look at an average testosterone decline of around 0.5% per year, give or take [1,2].

And it’s not just one or two studies. Similar findings have emerged in Denmark, Finland, Israel, and the United States [4–7].

And in 2025, researchers published one of the largest reviews to date, bringing together testosterone measurements of more than one million men across the globe [8]. They found a downward trend over the decades, even after accounting for age, body mass index (BMI), and differences in lab testing methods.

Younger men are seeing the steepest declines

More recently, another review added a twist. Looking at 170,000 men, researchers found that testosterone levels appear to be declining fastest among younger men. The population decline was almost 1% per calendar year in the under 30 bracket [2].

Of course, comparing blood results from different decades is a tricky thing – it’s complicated by changes in laboratory methods, sampling, and the men included in the research. Still, the numbers are getting harder and harder to ignore. And the real question is why.
 

Why are testosterone levels declining?

There’s no single explanation. Our lifestyles, diets, health, and environments have changed enormously over the past few decades. These are just some of the leading theories.

1. Obesity

It’s difficult to ignore the rise in obesity. According to the World Health Organisation (WHO), worldwide obesity has more than doubled since 1990 [9].

Being overweight interferes with the hormonal signals controlling testosterone production. Fat tissue converts testosterone into oestrogen, which signals the brain to slow down production. It also promotes insulin resistance, which can lower sex hormone-binding globulin (SHBG). SHBG is a protein that carries testosterone in the blood, so total testosterone falls.

These days, most of us eat too much and don’t move enough. Much of this has been sparked by the digital revolution; ecommerce, tech, and entertainment industries have boomed, which makes it easy to prioritise convenience over health. You can now order a Big Mac from your phone while you finish binge-watching your favourite Netflix series.

The digital age has transformed how we work too. We favour machinery and automation over manual labour. Many jobs are now office-based and some of us don’t even need to leave the house to work. Modern-day careers tend to be much less active than our grandfathers’, and people who lead sedentary lifestyles tend to have lower testosterone [10].

But we can’t blame it all on obesity. In the 2026 review, testosterone levels were declining even among men of a healthy weight [2]. And in some analyses, the decline was actually steeper in this group.

Clearly, something else going on.

2. External toxins

The annual global production of plastics has grown from 50 million to 460 million tons since the 70s [11,12]. Science is now seeing the connection between this and changes to our hormone health.

Many plastics contain endocrine-disrupting chemicals (EDCs), which, as their name suggests, can interfere with the body’s hormone balance. They can be natural or manmade. Some EDCs are slow to break down and accumulate, which makes them potentially hazardous over time, even in low doses.

When it comes to testosterone, the Endocrine Society specifically highlights phthalates as a potential culprit [13].

Phthalates are found in all kinds of products, including food and drinks containers, plastic wrappers, and fragranced products.

Other EDCs have been associated with lower semen quality and testosterone levels [14]. But it’s not clear how much these chemicals contribute to population-level changes.

3. Fewer smokers

This might surprise you, but data shows that smokers tend to have slightly higher testosterone levels than non-smokers [15]. Nicotine is metabolised by the body into cotinine; it’s possible this may prevent testosterone breakdown [15].

Globally, the percentage of male smokers has dropped from 41% in 1980 down to 32.6% in 2020 [16]. This may play a part in falling testosterone levels.

But that’s not a good reason to light up.

Smoking is extremely harmful to many systems in the body, and its dangers massively outweigh any potential effect it may have on testosterone. There are safe and natural ways to boost your testosterone. Smoking isn’t one of them.

4. Stress

Acute stress may cause testosterone levels to spike. But long-term stress is likely to lead to reduced testosterone levels [17].

Some say that, as a society, we’re more stressed than ever before. This one is up for debate. After all, a lot of modern-day problems are nothing new: recessions, political upheavals, and the demands of work and family.

One big difference is that we’re now constantly plugged in. We have phones in our pockets that ping with newsflashes and notifications, watches that buzz when a friend tries to make contact, and headphones that silence the real world around us. This constant stimulation can make it hard to switch off. And one of the biggest distractors is mobile phones.

Smartphone use has been linked to difficulties regulating emotions, impulsivity, addiction to social networking, shyness, low self-esteem, and FOMO (fear of missing out) [18]. From the physical aspect, it can also lead to sleep problems, reduced physical activity, and migraines [18]. Apps like TikTok and Instagram use algorithms to feed us content we like, which makes it even more difficult to separate ourselves.

5. Chronic illnesses and medications

Almost half of UK men (45.7%) report having a long-standing health condition [19].

Diabetes, chronic kidney disease, inflammatory illnesses, and certain infections can all interfere with testosterone production.

Some medications can have an effect too. Long-term opioid use and corticosteroid treatment are well-established examples, while statins generally have a much smaller effect. Evidence for antidepressants is mixed [20].

Researchers are even investigating whether changes in gut bacteria may have a role to play in declining testosterone, although this remains an emerging area of research.
 

How important is testosterone for men?

Testosterone is a sex hormone produced mainly in the testes. It plays an essential role in developing and maintaining typical male characteristics, including:

• Building muscle
• Growing body and facial hair
• Regulating sperm production

A lack of testosterone can lead to a variety of symptoms from fatigue to reduced sex drive.

Find out more about the symptoms of low testosterone.
 

Should we be worried?

Are we heading towards an impending Spermageddon?

While there’s a downward trend in sperm counts and testosterone levels, averages haven’t yet fallen to the point where they’re considered low for the overall population. The decline is gradual, so it’s not something you need to worry about specifically. But from an evolutionary and ecological perspective, it does raise interesting questions about the future of men’s health.

Testosterone deficiency is a separate problem, where levels drop enough to cause symptoms. If your levels are low or borderline, there are natural ways to boost testosterone. But some men need testosterone replacement therapy (TRT). Prescriptions have rocketed in recent years, highlighting it as a real issue for many men [21].

If you’re experiencing symptoms like reduced sex drive, fewer morning erections, or persistent fatigue, it’s worth investigating with a specialist, like Leger.
 

How can you check your testosterone levels?

There’s no need to routinely measure your levels, unless you’re curious or have symptoms of low testosterone.

Ideally, a testosterone blood test should be measured in the morning, after a good night’s sleep, and before breakfast. Low results generally need confirming with a repeat test.

You can check your levels with our Testosterone Blood Test or, for more insight into your hormone health, our Male Hormone Blood Test.

 

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References
 

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2. Negri F, Jiang T, Langroudi AP, Raffo M, Basran SS, Zhang CA, et al. Accelerating Decline in Serum Testosterone across Birth Cohorts: A Systematic Review and Meta-Regression Analysis. World J Mens Health. 2026;44. doi:10.5534/wjmh.260136
3. Levine H, Jørgensen N, Martino-Andrade A, Mendiola J, Weksler-Derri D, Jolles M, et al. Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries. Hum Reprod Update. 2023;29: 157–176. doi:10.1093/humupd/dmac035
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