If you're often tired as a man, the cause usually sits in a handful of things you can check in your blood: your iron, your vitamin D, your vitamin B12, your thyroid and sometimes your testosterone. A blood test doesn't always find a cause, and that's useful information too. From around age 30 your testosterone drops by roughly 1% a year on average, so "it's probably just age" isn't always the full story.
Honestly? Most pieces on fatigue talk to everyone at once. But as a man you have a few causes that get overlooked fast. That's what this article is about.
Why are you always tired as a man?
Fatigue is almost never one thing. It's often a sum of sleep, stress, movement and food, sometimes with a physical factor underneath that shows up in your blood. Those last ones are the easy part to check.
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: an unstable blood sugar can leave you flat.
One thing stands out: in men, the hormonal side gets recognised late. A slow thyroid is still seen as "a women's thing", while men get it too.
Which blood values relate to fatigue?
For tiredness, the usual values are iron, vitamin D, vitamin B12, the thyroid and blood sugar, and for persistent complaints 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 there's anaemia. In research with non-anaemic women, iron improved fatigue (Verdon, 2003). Read more on iron deficiency in men.
Vitamin D. In the Dutch winter your skin makes little vitamin D. A low vitamin D can go together with fatigue and a flat mood. More on this: vitamin D deficiency in men.
Vitamin B12. A shortage of vitamin B12 can cause tiredness, tingling and trouble concentrating. If you eat little or no animal products, the risk of a shortage is higher. Read more on vitamin B12 deficiency.
Thyroid. A slow thyroid, read from TSH and free T4, makes many people tired, cold and sluggish. In men it's suspected less quickly.
Testosterone. Low energy, less interest in sex and less muscle strength can go together with a low testosterone. There's more on this in our guide to male hormonal health.
Tired and flat: can testosterone be the cause?
With persistent tiredness alongside less interest in sex, a shorter fuse or less muscle strength, a low testosterone can play a role. It's rarely the only cause, but in men it gets skipped too often.
Two things matter if you have this measured. Testosterone is highest in the morning, so a reliable reading is taken early in the day. And from age 30 the value drops gradually, by about 1% a year on average (Harman, 2001).
Also read: men's health after 40 and which tests are relevant then.
Which check fits your symptoms?
The overview below links common symptom patterns to the blood value that often fits. See it as a starting point for the conversation with your GP, not a diagnosis.
| Your symptoms | Blood value that is often relevant | Worth knowing |
|---|---|---|
| Tired, pale, short of breath on exertion | Iron and ferritin | A low ferritin can play a role even without anaemia |
| 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, slow digestion | Thyroid (TSH, free T4) | More often overlooked in men |
| Tired, less interest in sex, less muscle strength | Testosterone | Measure in the morning, when the value is highest |
| Tired, very thirsty, frequent urination, overweight | Blood sugar (glucose, HbA1c) | Discuss any abnormal values with your GP |
| Tired despite normal results | Often sleep, stress or lifestyle | Blood isn't always the answer, and that's information too |
No single row is a conclusion. They're leads that help you look more precisely.
When is fatigue not in your blood?
Often tiredness doesn't come from a shortage, but from sleep, stress or a packed schedule. Then your blood can look fine while you feel awful. That isn't a missed cause, it's an important result.
Poor sleep, long-term stress and too little movement are common energy drains. 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 unsure whether it's burnout or a low testosterone? We cover those separately.
Do the complaints last longer than a few weeks, or do other symptoms join them? Discuss it with your GP.
Frequently asked questions
Can you see fatigue in your blood?
Sometimes yes, sometimes no. A blood test can show shortages and abnormalities linked to tiredness, but for some people the result stays normal. That helps you forward too.
Which blood test is useful for tiredness?
A test that covers iron, vitamin D, vitamin B12 and the thyroid catches the most common causes. In men, testosterone can be a useful addition.
Do I need to fast for this blood test?
For some values, such as 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's no fixed answer. Some men test periodically to build a picture over time. What fits you is something to discuss with your GP.
Getting started
Want to know whether a physical factor sits under your tiredness before you see your GP? The Complete Men's Health Panel maps a number of these markers, so you go into the conversation informed.
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.
- Roy S, Sherman A, Monari-Sparks MJ, et al. Correction of low vitamin D improves fatigue: effect of correction of low vitamin D in fatigue study (EViDiF study). North Am J Med Sci. 2014;6(8):396-402. PMID: 25210673.
- Verdon F, Burnand B, Stubi CL, et al. Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial. BMJ. 2003;326(7399):1124. PMID: 12763985.
- NHG-Standaard Schildklieraandoeningen. Nederlands Huisartsen Genootschap (Dutch College of General Practitioners).
Disclaimer
Caliberhealth works with BIG-registered doctors who assess your blood results. This article gives general information and is not a substitute for medical advice from a GP or specialist. A blood test is a tool to go into the conversation with your doctor better informed, not a diagnosis in itself. For serious symptoms or health concerns, contact your GP, or in an emergency call 112.
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