After 30, your testosterone drops by roughly 1 percent a year on average. That is normal, and it happens slowly. But sometimes it falls faster or further than your age can explain.
What I notice in practice: a lot of men reach straight for a pill or a supplement. When the first question is where the drop actually comes from.
There are broadly two routes. The difference between them decides almost everything that follows.
Primary or secondary hypogonadism: what is the difference?
Low testosterone has two broad sources. In primary hypogonadism the testes themselves work less well, and your brain pushes harder: LH and FSH go up. In secondary hypogonadism the pituitary and hypothalamus send less signal, so LH and FSH are low or low-normal instead. The same number can mean two different things.
That is why a good hormone test shows not only testosterone, but also LH and FSH. Those two point the direction.
In the large EMAS study, complaints only clearly tracked with a testosterone below roughly 11 nmol/l (Wu, 2010). Above that line the link weakened quickly.
Which signs go with low testosterone, you can read in the overview low testosterone in men.
1. Age
A common cause is simply getting older. In the Baltimore Longitudinal Study of Aging, testosterone in healthy men declined gradually with age, independent of illness (Harman, 2001).
With age the picture is often mixed. Both the testes and the drive from the brain ease off a little, and the LH can be normal or slightly raised.
My note: age explains a slow decline, not a sudden dive. If you drop far at 35, I keep looking.
2. Excess weight and belly fat
Fat tissue is not passive. It contains the enzyme aromatase, which converts testosterone into estrogen. More belly fat can push your testosterone down (Kelly, 2015).
The link runs both ways. Low testosterone makes weight gain easier, and more fat can lower testosterone further.
Take a man of 45, BMI 31, with a testosterone of 9 nmol/l. His LH is low-normal. That fits a secondary picture, in which the excess weight plays into the signalling.
His number alone says nothing about the cause. The LH beside it does. This is the cause where lifestyle can often make a real difference, though it is never guaranteed.
3. Chronic stress
Under long-term stress your cortisol stays high. And cortisol can suppress testosterone directly. In a classic experiment, testosterone fell within a few hours of a cortisol spike (Cumming, 1983).
Stress also dampens the drive to the testes through the brain. That again points towards the secondary picture.
How stress works on your hormones is covered in cortisol and testosterone. If you are torn between stress and low testosterone, read burnout or low testosterone.
4. Poor or too little sleep
You make a large share of your testosterone at night, tied to your sleep. When young men slept only five hours for a week, their daytime testosterone dropped by 10 to 15 percent (Leproult, 2011).
That is not a disease, but it is a dial many men keep turning without noticing.
Sleep is easy to overlook in this list.
5. Certain medication
Some medicines can lower testosterone. Opioids (strong painkillers) and corticosteroids are known for this effect, and the odd other drug can play in too.
Important: never stop prescribed medication on your own. If you suspect a drug is involved, that is a conversation with your GP, not a decision you make alone.
6. An underlying condition
Sometimes a specific condition sits behind it. Think of a problem in the pituitary or the testes themselves, of haemochromatosis (iron overload), or of an underactive thyroid.
These causes are less common. This is exactly where the primary versus secondary split matters. A high LH with low testosterone points to the testes, a low LH to the pituitary.
This is the kind of situation where you should not puzzle it out alone, but let your GP look with you.
7. Deficiencies and lifestyle
Finally, lifestyle and nutrient shortfalls play a part. Heavy alcohol use, little exercise and a chronic shortage of, say, zinc or vitamin D are linked with lower testosterone.
Mind the word linked. Topping up a deficiency is no guarantee of more testosterone. Only when there is a real shortfall can it make any difference.
Overview: which cause points which way
This overview ties each cause to primary or secondary, and to the blood value that gives direction. Treat it as a thinking aid, not a diagnosis.
| Cause | Primary or secondary | Which blood value points that way |
|---|---|---|
| Age | Often mixed | Testosterone gradually lower, LH normal to slightly raised |
| Excess weight | Secondary | Testosterone low, LH low-normal, SHBG often low |
| Chronic stress | Secondary | Testosterone low, LH low-normal |
| Sleep loss | Secondary | Testosterone low, LH low-normal |
| Medication | Primary or secondary | Depends on the drug; LH gives direction |
| Testes or pituitary | Primary (testes) or secondary (pituitary) | High LH and FSH at the testes, low at the pituitary |
| Deficiencies and lifestyle | Secondary | Testosterone low; zinc, vitamin D and ferritin as context |
What can you have measured?
There is no blood test that points to the one cause. But the combination of testosterone with LH and FSH gives direction: together they show whether the problem sits in the testes or in the signalling. Your GP often looks at SHBG too, and sometimes at prolactin or ferritin.
The NHG gives GPs a guide to which causes fit these complaints and which values go with them. What you need, your GP decides together with you.
Separate pages on total testosterone, LH and FSH explain what each value means.
If you want those values mapped together, the Men's Hormones panel brings your hormonal values into one place. Always discuss the result with your GP; the number is a starting point, not an endpoint.
How to measure testosterone properly, with a morning draw and the right extra values, is in how to test testosterone. If it stays low for a long time, we cover the consequences of long-term low testosterone separately.
My advice stays simple. Do not chase a single number, look at the cause and the context around it. For the broader background on men's hormones, see men's hormonal health.
References
- Harman SM, Metter EJ, Tobin JD, Pearson J, Blackman MR. 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.
- Kelly DM, Jones TH. Testosterone and obesity. Obes Rev. 2015;16(7):581-606. PMID 25982085.
- Cumming DC, Quigley ME, Yen SS. Acute suppression of circulating testosterone levels by cortisol in men. J Clin Endocrinol Metab. 1983;57(3):671-673. PMID 6348068.
- 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.
- 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.
- Dutch College of General Practitioners (NHG). Guide to causes and blood values in men's complaints.
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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