You're tired, your libido is flat and you train just as hard as last year, yet your muscles barely respond. The easy conclusion is: my testosterone is too low. Sometimes that's true. Often the story is a bit more complicated.
Testosterone in men declines gradually, by roughly 1% per year from your thirties or forties onward (Harman, 2001). Still, a low number on a lab report doesn't automatically mean symptoms. And symptoms don't automatically mean a low number. In the large European EMAS study, only a small share of men with a low value actually had the matching symptoms (Wu, 2010).
An important detail from other research: age isn't the only factor. Weight gain and your general health sometimes lower your testosterone as much as the years themselves (Travison, 2007).
Here's what I'll give you below: 10 signs that may point to low testosterone. For each one I note what else could be causing it. That way you can see when a blood test makes sense, and when you're on the trail of something else.
No single sign proves anything on its own.
How do you know if your testosterone is too low?
In short: from a combination of symptoms and a blood value, not from either one alone. A low value without symptoms says little. Symptoms without a measurement can also come from stress, poor sleep or another condition. Only when both sides point the same way does the picture get clearer.
Think of it as two witnesses telling the same story. One witness is weak, two that agree are a lot more convincing. Always discuss that with your GP.
What does testosterone actually do in your body?
Testosterone is the main male sex hormone. It plays a role in your sex drive, your erections, your muscle mass and strength, your bone density, your mood and partly your energy. Your testes make it, steered by the hormones LH and FSH from your brain. So a problem can sit in two places: in the testes themselves, or in the signalling.
LH works like a gas pedal towards your testes. If your testosterone is low while your LH is high, that points more to the testes. If your LH is low too, the problem sits higher up.
I often describe testosterone as recovery currency: the hormone your body refuels with after effort, sleep and stress. Run that currency down, and you notice it in several places at once.
That broad role is exactly why low testosterone is so confusing. One hormone with a hand in everything gives complaints that could just as easily come from somewhere else.
In blood you usually look at total testosterone, free testosterone and SHBG, the protein that binds testosterone. Those three together say more than a single number. Below are the signs to watch for.
1. Less interest in sex
A falling libido is one of the symptoms that most consistently links to low testosterone (Wu, 2010). If you notice much less interest for weeks or months while nothing else is going on, that can be a signal.
Note the nuance. Sex drive is also tied to stress, your relationship, sleep and medication such as some antidepressants. Testosterone is one of the dials, not the only one.
What strikes me: this is often the first thing to change, and the last thing men talk about. That's exactly why it's a gauge worth taking seriously.
2. Erection problems and fewer morning erections
Erections run mostly on blood vessels, and only then on hormones. So an erection problem is far from always a testosterone problem. In the Massachusetts Male Aging Study, erectile dysfunction was strongly linked to vascular and lifestyle factors (Feldman, 1994).
What does stand out with low testosterone: fewer spontaneous morning erections and less desire leading up to sex. If that's your picture, it can be useful to include your hormones in the search.
If your morning erections keep coming, that points away from your hormones more often. That small detail saves you a lot of wrong searching sometimes.
3. Persistent fatigue and low energy
Many men with low testosterone describe a flat tiredness that a weekend of rest doesn't fix. Yet fatigue is the trickiest signal, because it has a huge range of possible causes.
Sleep debt, an underactive thyroid, anaemia and a busy period give exactly the same feeling. If you suspect burnout, first read the difference between burnout and low testosterone.
In my experience, fatigue on its own is the weakest evidence on the whole list.
4. Loss of muscle mass and strength
Testosterone helps build and keep muscle. If you train the same and still lose strength and muscle volume, low testosterone can be one of the puzzle pieces. Research that temporarily suppressed testosterone showed clear loss of muscle mass (Finkelstein, 2013).
The effect has been measured the other way too. Higher testosterone levels went together with more muscle mass and strength (Bhasin, 1996). So the hormone really is a building block, not a side note.
What stands out to me with training: men blame their hormones quickly, while recovery, protein intake and sleep are often the first suspects.
5. More belly fat that's hard to lose
Between belly fat and testosterone, traffic runs both ways. Fat tissue can convert testosterone into oestrogen, and a lower testosterone can make it easier to store fat. That can create an annoying circle.
Finkelstein showed that in men it's the oestrogen that helps regulate body fat (Finkelstein, 2013). That oestrogen partly comes from their own testosterone.
If you gain around your waist without your eating really changing, it can be worth looking at your hormones and your fasting glucose alongside lifestyle.
6. Low or irritable mood
Low testosterone is sometimes associated with a down or short-fused mood. It's not a one-to-one link: depressive symptoms often have several causes at once.
It also works both ways. Depression can lower your testosterone, and low testosterone can affect your mood.
If your mood and your energy dropped together, that's a reason to take it seriously and discuss it with your GP, not to conclude on your own that it's your testosterone.
7. Trouble concentrating and brain fog
Some men with low testosterone describe a woolly feeling in their head: trouble focusing, forgetting things faster, feeling less sharp. The science here is still cautious, so treat this as a possible signal, not as proof.
Poor sleep and chronic stress give the exact same brain fog. There's often more to gain there than in a single hormone number.
I stay deliberately careful with this one. Brain fog is genuinely annoying, but it rarely points in just one direction.
8. Sleeping worse
Sleep and testosterone are closely linked. You make most of your testosterone during sleep, and even a week of poor sleep can lower the value noticeably in healthy young men (Leproult, 2011).
That makes sleep a double-edged sword: poor sleep can push your testosterone down, and low testosterone can disturb your sleep. So start with your nights before drawing conclusions.
If you snore heavily and still feel wiped out during the day, mention sleep apnea to your GP too. It disrupts your nights and your hormones at the same time.
9. Less body hair and slower beard growth
Testosterone and its derivative DHT drive your beard and body hair. If over a longer time you notice you shave less often or that body hair thins, that can fit a lower androgen level.
This is a slow and very personal signal, because hair growth is also strongly hereditary. Only take it seriously alongside other symptoms.
Bald crown or not, that on its own says little about your testosterone.
10. Lower bone density over the long term
You don't feel this signal, and that's exactly what makes it important. Testosterone helps keep your bones strong. Long-term low testosterone is associated with lower bone density, which over time can raise the risk of fractures.
You usually only notice it when something breaks. That's why it belongs on the list, even though it sits at the bottom. Read more in the consequences of long-term low testosterone.
A bone density scan isn't part of a blood test. That's something your GP can request when there's reason to.
Why you shouldn't read these signs in isolation
Almost every sign above has a lookalike. Fatigue can come from your thyroid, belly fat from your diet, low mood from a hard stretch. So I put them in a table next to their most common alternative causes, with the value that adds context.
| Sign | Could also come from | Which value adds context |
|---|---|---|
| Little interest in sex | Stress, relationship, antidepressants | Total testosterone, free testosterone |
| Persistent fatigue | Sleep debt, thyroid, anaemia | Testosterone, TSH, ferritin |
| More belly fat | Diet, too little movement | Testosterone, SHBG, fasting glucose |
| Low mood | Burnout, depression | Testosterone, cortisol |
| Erection problems | Blood vessels, medication, stress | Testosterone, glucose, cholesterol |
Don't read the table as a diagnosis machine. It only helps you work out what else you'd want to know before you hang anything on a single number.
When are these signs really low testosterone?
When several signs appear together, last longer and can't be explained by something obvious like a heavy work period or a few bad nights. A single sign is rarely enough. The NHG and RIVM stress that a symptom like fatigue often has several causes at once. A blood test helps you sort the options, not make a diagnosis on your own.
Take two men aged 48, both with a testosterone of 12 nmol/l. One trains, sleeps well and feels fine. The other is chronically tired, has gained eight kilos and has no interest in sex. Same number, completely different story.
For the first man, 12 nmol/l is simply his normal. For the second, it fits a string of complaints that together do point somewhere. That's exactly why the value alone never decides: your symptoms belong with it.
The message isn't that the number doesn't count. It does, but always together with the story around it. A value, plus your symptoms, plus your lifestyle gives your GP something to work with.
What you can do now
Do you recognise several of these signs and do they persist? Then it's worth bringing your hormones into view and discussing it with your GP. First jot down which complaints you have and how long they've been there, so you're on firmer ground in that conversation.
With the Testosterone Panel you measure total testosterone, free testosterone and SHBG in one go. Every result gets an assessment from a BIG-registered doctor, so you're not left with a bare number.
Want to read on? See the 7 causes of low testosterone, how to measure testosterone properly and what a normal testosterone level by age is. For a broader view of your hormones there's the pillar hormonal health in men.
Sources
- Wu FC, Tajar A, Beynon JM, et al. Identification of late-onset hypogonadism in middle-aged and elderly men. N Engl J Med. 2010;363(2):123-135. PMID 20554979.
- Feldman HA, Goldstein I, Hatzichristou DG, et al. Impotence and its medical and psychosocial correlates: results of the Massachusetts Male Aging Study. J Urol. 1994;151(1):54-61. PMID 8254833.
- Harman SM, Metter EJ, Tobin JD, et al. Longitudinal effects of aging on serum total and free testosterone levels in healthy men. Baltimore Longitudinal Study of Aging. J Clin Endocrinol Metab. 2001;86(2):724-731. PMID 11158037.
- Travison TG, Araujo AB, Kupelian V, et al. The relative contributions of aging, health, and lifestyle factors to serum testosterone decline in men. J Clin Endocrinol Metab. 2007;92(2):549-555. PMID 17148559.
- Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. 2011;305(21):2173-2174. PMID 21632481.
- Bhasin S, Storer TW, Berman N, et al. The effects of supraphysiologic doses of testosterone on muscle size and strength in normal men. N Engl J Med. 1996;335(1):1-7. PMID 8637535.
- Finkelstein JS, Lee H, Burnett-Bowie SM, et al. Gonadal steroids and body composition, strength, and sexual function in men. N Engl J Med. 2013;369(11):1011-1022. PMID 24024838.
- NHG guidance and Thuisarts.nl, general information on fatigue and men's health. Dutch College of General Practitioners.
- RIVM, general information on health and lifestyle. National Institute for Public Health and the Environment.
Disclaimer
Caliberhealth works with BIG-registered doctors who review your blood results. This article offers general information and does not replace medical advice from your GP or specialist. A blood test is a tool, not a diagnosis on its own. For persistent or serious symptoms, contact your GP, or call 112 in an emergency.
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