Why do Gen Z and millennial men have lower testosterone levels?
Odds are your grandad had higher testosterone levels than you — but why?
For decades, testosterone levels have been declining. Your grandad may not have been quite as swift with Excel, but he probably one-upped you where T levels are concerned.
It’s normal for testosterone levels to decline as you get older, but for some reason, there’s been a population-level drop with each generation, at least since the 70s [1–4]. This means, on average, Gen Zers and millennials have significantly lower testosterone levels compared to their predecessors.
But what is it about younger generations that has caused this trend?
In this article, we look at:
- The generational decline in testosterone
- Why are testosterone levels falling?
- How important is testosterone for men?
- Should I be worried?
- Measuring your testosterone levels
The generational decline in testosterone
The average testosterone level of a 60-year-old man in 1987 was around 17.5nmol/L, according to a 2007 study in Massachusetts . Compare that to a 60-year-old man in 2002 — his testosterone level was closer to 15nmol/L.
Based on this, average testosterone levels in men are declining by 1% every year, give or take.
Research carried out on Finnish and Danish populations has shown the same trend [1,6]. And even more recently, a large-scale study of Israeli men has shown how average testosterone levels have dropped between 2006 and 2019  — by over 10% across almost every age category.
Of course, we can’t know for certain that 60-year-old millennials and Gen Zers will have lower testosterone levels, at least not for a few decades, but it’s looking very likely.
What’s concerning is testosterone levels aren’t the only problem. Sperm counts are dropping significantly  and some reproductive disorders, like testicular cancer, are on the rise (9). Even men’s grip strength has declined . So, what’s going on?
Why are testosterone levels falling?
This is a complicated question. The truth is, it’s not entirely clear, and it likely comes down to a combination of factors.
1. Obesity and sedentary lifestyles
Rising rates of obesity almost certainly play a role in declining testosterone levels. Being overweight can push the body’s hormone axis out of balance and affect how the body responds to insulin, both of which can lower testosterone levels . One study found that an increase in BMI by four to five points was associated with a testosterone level of someone ten years older .
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 to be delivered to your house while you finish binge-watching your favourite Netflix series. It’s something Baby Boomers wouldn’t have dreamed of and something Gen Zers can’t imagine a world without.
The digital age has transformed how we work too. We favour machinery and automation over manual labour, which likely explains the drop in men’s grip strength over time. 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 .
But even after taking obesity into account, most studies still show a downward trend in testosterone, which means it can’t be the only culprit.
2. External toxins
The annual global production of plastics has grown from 50 million to 300 million tons since the 70s . Science is now seeing the connection between this and changes to our hormone health.
Many plastics contain endocrine-disrupting chemicals (EDCs). EDCs, as their name suggests, are chemicals that interfere with the body’s hormones and may be natural or man-made. Some EDCs are slow to break down and accumulate which makes them potentially hazardous over time, even in low doses.
EDCs are found in everyday products, including:
- Plastic bottles
- Food storage containers
- Liners of metal food cans
Research has found links between EDC exposure and effects on attention (ADHD), immunity, metabolism, puberty, and reproduction . Several EDCs have been associated with lower semen quality and testosterone levels , so there’s a possibility they may be partly to blame for this population-level decline.
3. Fewer smokers
This might surprise you, but some data shows that smoking marginally increases testosterone levels [16,17], though not all studies agree with this. Nicotine is metabolised by the body into cotinine; it’s possible this may prevent testosterone breakdown .
In the 70s, half of men smoked , but since then there’s been a significant decrease. Now in the UK, only around 15% of men smoke . 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 — and smoking isn’t one of them.
4. Stress and mental health problems
Acute stress may cause testosterone levels to spike. But both physical and psychological long-term stress is likely to lead to reduced testosterone levels [19,20].
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. Everything is immediate: we just need to press a button and we have access to any information we please. This constant stimulation can make it hard to switch off. And one of the biggest distractors is mobile phones.
Most children are phone owners by the age of seven, a report from Childwise showed , and it comes with implications.
Smartphone use has been linked to difficulties regulating emotions, impulsivity, addiction to social networking, shyness, low self-esteem, and FOMO (fear of missing out) . From the physical aspect, it can also lead to sleep problems, reduced physical activity, and migraines . Apps like TikTok and Instagram use algorithms to feed us content we like, which makes it even more difficult to separate ourselves.
There are, of course, upsides to smartphones and social media. Some argue that digital communication can improve friendships and connections , or that it may inspire, motivate, and give us new knowledge . Might this just be a new normal that we’re adjusting to? Gen Zers could represent the start of a new wave of how we connect with one another. They’re the first generation to use smartphones, tablets, and social media from such a young age - and we’re still not entirely sure what the lifelong effects of this might be.
5. Other causes
Above are just a few reasons that might explain declining testosterone levels.
Other more off-the-wall theories have been put forward too, like tighter-fitting underwear and warmer temperatures in homes and offices . (There’s a reason your crown jewels hang away from your body.)
Conditions like diabetes have also become much more common. People with diabetes tend to have lower testosterone, though it’s not entirely clear which causes which (26).
But one thing we can be sure of — there’s no single cause for these downward trends. It likely comes down to a combination of changes in our lifestyles, environment, and behaviours.
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.
Should I 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 and reproductivity.
Testosterone replacement therapy (TRT) prescriptions have rocketed in recent years (29). While this is mainly due to changes in our approaches to management and media influences, there has been a genuine increase in the number of men with testosterone deficiency (30).
Measuring your testosterone levels
There’s no need to measure your testosterone levels routinely unless you have signs or symptoms of low testosterone. If this is the case, it’s best to let a doctor know exactly what you’re experiencing so they can interpret your results alongside your symptoms.
Alternatively, you can check your levels from home with our Testosterone Blood Test — it’s a simple finger-prick test you can take yourself. You’ll receive a report from one of our doctors with your result and you can then see how your testosterone levels compare to other men your age.
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