You down three coffees before lunch, you have no drive for the gym, and by eight in the evening you are already nodding off on the couch. Not one bad week, but month after month the same. At moments like that the cause often sits with a handful of things you can simply check in your blood: your iron, your vitamin D, your vitamin B12, your thyroid and sometimes your testosterone.
Honestly? Most pieces on fatigue address everyone at once. But as a man you have a few causes that are routinely overlooked, especially on the hormonal side. That is what this guide is about: what you can measure, how to read it, and when blood is not the answer.
Why are you always tired as a man?
Fatigue is almost never one thing. It is often the sum of sleep, stress, exercise and diet, sometimes with a physical factor underneath that shows up in your blood. Those last ones are relatively easy to check, yet they stay undiscovered the longest.
Roughly, the physical causes fall into a few groups:
- Deficiencies: iron, vitamin D and vitamin B12 are among the most common.
- Hormones: your thyroid and your testosterone both drive your energy.
- Metabolism: a disrupted blood sugar can leave you flat.
What stands out: in men the hormonal side is recognised late. An underactive thyroid is still seen as "a women's thing", while men get it just as well. My stance: if you have been tired for months and nobody has looked at your thyroid and testosterone, the story is not finished.
Which blood values relate to fatigue?
For tiredness, the usual checks are iron, vitamin D, vitamin B12, the thyroid and blood sugar, and with ongoing symptoms sometimes testosterone. No single value proves the cause on its own, but together they sketch a picture you can discuss with your GP.
Iron and ferritin. Ferritin is your iron store. A low ferritin is sometimes linked to fatigue, even before anaemia is present. The Dutch College of General Practitioners (NHG) treats iron and ferritin as a standard part of the workup for persistent fatigue. Read more about iron deficiency in men.
Vitamin D. In the Dutch winter your skin makes little vitamin D, as the Dutch Health Council (Gezondheidsraad) explains. A low vitamin D can go with fatigue and a flat mood. More on this: vitamin D deficiency in men.
Vitamin B12. A shortage of vitamin B12 can cause fatigue, tingling and trouble concentrating. If you eat little or no animal products, the risk of a shortage is higher, according to the Netherlands Nutrition Centre (Voedingscentrum). Read more about vitamin B12 deficiency.
Thyroid. An underactive thyroid, read from TSH and free T4, leaves many people tired, cold and sluggish. In men it is suspected less quickly, while according to the NHG it occurs in them too.
Testosterone. Low energy, reduced sex drive and less muscle strength can relate to a low testosterone. More on this in our guide to men's hormonal health.
Blood sugar. A disrupted metabolism can cause sluggishness. When in doubt, fasting glucose and HbA1c are often checked, the latter giving an average over recent weeks.
Tired and listless: can testosterone be the cause?
With persistent fatigue together with reduced sex drive, a shorter fuse or less muscle strength, a low testosterone can play a role. It is rarely the only cause, but in men it is skipped too often.
Two things matter if you measure this. Testosterone is highest in the morning, so a reliable measurement is taken early in the day. And from your thirties the value declines gradually. Alongside total testosterone, free testosterone sometimes adds nuance. Also read: men's health after 40 and which tests are relevant then, and if you want to work on your values, boosting testosterone naturally.
How do you read your result without falling into traps?
A result on paper tempts you toward quick conclusions, and that is often where it goes wrong. A few things help you read your values honestly.
Within the reference range is not the same as optimal for you. Reference values describe what is common in a large group, not what is best for you. A ferritin or vitamin D at the low end of normal can still be worth discussing when you have symptoms. At the same time, a value just outside the reference is not automatically the explanation for your fatigue. It is about the pattern, not a single number.
A snapshot is not a trend. Many values fluctuate. Testosterone and cortisol differ by time of day, vitamin D differs by season, and ferritin can rise temporarily during inflammation or infection. A second measurement after a few weeks often says more than a one-off result. That is exactly why some men test periodically: not to chase a single number, but to see a line over time.
One abnormality does not rule out the rest. If you find a low vitamin D, it is tempting to stop looking. But fatigue is often a sum. For persistent symptoms the NHG therefore looks beyond a single marker, and also weighs sleep, mood and lifestyle. Discuss your full picture with your GP rather than crowning one result as the cause.
How do you prepare for a reliable measurement?
The quality of your result starts with how you test. A few practical points make the difference between a usable and a misleading value.
- Timing for hormones. Have testosterone and cortisol measured in the morning, ideally before 10:00, because both are highest then and decline afterward.
- Fasting for blood sugar. For a fasting glucose, not eating for several hours beforehand is advised. HbA1c does not require fasting, because it reflects an average over weeks.
- Recent exercise and infections. A hard workout can temporarily affect markers such as ferritin and inflammation values. If you have just been ill, that can distort the picture. Schedule your test for a calm moment.
- Supplements. If you take vitamin B12 or vitamin D, for example, mention it to your doctor, because it colours the interpretation.
The Netherlands Nutrition Centre (Voedingscentrum) stresses that diet and lifestyle shape your values over time, while a snapshot is mainly a starting point. So treat your result as a photo, not a film.
Which check fits your symptoms?
The overview below links common symptom patterns to the blood value that often fits. Treat it as a starting point for the conversation with your GP, not a diagnosis.
| Your symptoms | Blood value often relevant | Point to note |
|---|---|---|
| Tired, pale, short of breath on exertion | Iron and ferritin | Even without anaemia a low ferritin can play a role |
| Tired, flat mood, little daylight | Vitamin D | Often lower in the Dutch winter |
| Tired, tingling, forgetful, plant-based diet | Vitamin B12 | Few animal products raises the risk of a shortage |
| Tired, cold, weight gain, sluggish bowels | Thyroid (TSH, free T4) | Overlooked more often in men |
| Tired, low sex drive, less muscle strength | Testosterone | Measure in the morning, when it is highest |
| Tired, very thirsty, frequent urination, overweight | Blood sugar (glucose, HbA1c) | Discuss abnormal values with your GP |
| Tired despite normal results | Often sleep, stress or lifestyle | Blood is not always the answer, and that is information too |
No row is a conclusion. They are leads that help you look more precisely.
Three stubborn myths about fatigue in men
A few beliefs around fatigue send men down the wrong path unnecessarily. It pays to set them straight.
"It is probably just my age." Testosterone does decline gradually from your thirties, but that does not mean every symptom is explained by it. An underactive thyroid, a low ferritin or a vitamin B12 deficiency have nothing to do with age and are very treatable. Age is a factor, not an excuse to skip looking.
"An underactive thyroid is a women's thing." Thyroid problems are more common in women, but men get them too. Precisely because it is expected less, it stays undiscovered longer in men. The NHG counts thyroid testing among the standard repertoire for persistent fatigue, regardless of sex.
"If my blood is fine, I am just making it up." Nonsense. A normal result does not mean your symptoms are imagined, but that the cause probably does not lie in a deficiency. Sleep, stress, workload and mood are real causes, even if you do not see them on a result sheet. A normal result is a signpost, not a verdict.
When is fatigue not in your blood?
Often tiredness does not come from a deficiency, but from sleep, stress or an overloaded schedule. Then your blood can look perfectly fine while you feel awful. That is not a missed cause but an important result: it points the search toward the rest of your lifestyle.
Poor sleep, prolonged stress and too little exercise are common energy drains. For fatigue complaints the NHG stresses the importance of sleep, exercise and recovery alongside any blood testing. A blood test then mainly rules out the physical causes, so you can focus on the rest.
Do you feel tired despite enough sleep, or are you torn between burnout or low testosterone? We cover those separately. If symptoms last longer than a few weeks, or other symptoms appear, discuss it with your GP.
Frequently asked questions
Can you see fatigue in your blood?
Sometimes yes, sometimes no. A blood test can show deficiencies and abnormalities linked to tiredness, but for some people the result stays normal. That also helps you move forward.
Which blood test is handy for fatigue?
A test that maps iron, vitamin D, vitamin B12 and the thyroid covers the most common causes. In men, testosterone can be a useful addition.
Do I need to fast for such a blood test?
For some values, like blood sugar, fasting is advised. For testosterone the timing matters most: the morning. Read the instructions with your test carefully.
How often should I have this checked?
There is no fixed answer. Some men test periodically to build a picture over time. What fits you is something to discuss with your GP.
What is the difference between total and free testosterone?
Total testosterone measures all the testosterone in your blood, including the portion bound to proteins and therefore not directly available. Free testosterone is the smaller, unbound portion your body can use straight away. Sometimes your total testosterone is normal while you have symptoms, and free testosterone can add nuance. Which measurement is useful for you is something you decide together with your doctor.
Can fatigue also come from blood sugar?
A disrupted metabolism can cause sluggishness. Persistent thirst, frequent urination and being overweight are signals where glucose and HbA1c come into view. Always discuss abnormal values with your GP.
Getting started
Want to know whether a physical factor sits under your fatigue before you see the GP? The Complete Men's Health Panel maps several of these markers, so you enter the conversation informed. To highlight the hormonal side, the Hormones Man panel looks more specifically at your hormones.
In closing
Caliberhealth works with BIG-registered doctors who review your blood results. This article offers general information and does not replace advice from a GP or specialist. A blood test is a tool to help you enter the conversation with your doctor better informed, not a diagnosis on its own. For serious symptoms or health concerns, contact your GP, or call 112 in an emergency.
Author
Caliberhealth
Dr. Naimi, BIG-registered physician, oversees the medical standards behind our content and assessments. Read our medical policy
