It is half past two in the morning and you are wide awake, while during the day you can barely keep your eyes open. You have already worked through the sleep-hygiene checklist: no screens in bed, a cool bedroom, fixed bedtimes. And still it persists. That is where this article comes in: could something physical be behind it, and can you see it in your blood?
First the nuance: there is no blood test that measures sleep quality. A vial of blood cannot tell you how deeply you sleep or how often you wake up. What blood can do is reveal treatable causes that sabotage your night's rest. And that is exactly where things often go wrong in practice: with stubborn sleep complaints, the thyroid and iron are in my view still skipped too easily.
Sleep and blood influence each other in two directions
The link runs both ways, which makes it hard to untangle. Too little or restless sleep can go together with more cravings for sugar, a more erratic blood-sugar pattern and higher perceived stress. The other way around, a physical issue such as an overactive thyroid or low iron can disturb your sleep. One bad night is no problem; weeks in a row are.
The Dutch Nutrition Centre (Voedingscentrum) points out that irregular eating and caffeine late in the day can disturb night-time rest, while the Health Council (Gezondheidsraad) emphasises in its movement guidelines that enough daylight and activity during the day are associated with a better sleep rhythm. In other words: lifestyle is the first dial to turn before you look at your blood.
Which blood values can play a role in sleep complaints?
With persistent complaints it can be worth ruling out physical causes. The table below shows which value fits which pattern, and roughly what a deviation can mean. These are guidelines, not diagnoses.
| Blood value | Possible link with sleep | Rough point of attention |
|---|---|---|
| TSH (and free T4) | An overactive thyroid can cause restlessness and waking up; an underactive one daytime drowsiness | TSH outside roughly 0.4-4.0 mU/L deserves a doctor's explanation |
| Ferritin | Low iron is linked to restless legs and broken sleep | Complaints can occur below 30 ug/L, even without anaemia |
| Glucose (fasting) | Swinging blood sugar can contribute to night-time waking | Fasting 5.6-6.9 mmol/L falls in the prediabetes range |
| Vitamin D | A deficiency is often linked to general fatigue | In winter a low level in the Netherlands is the rule rather than the exception |
| Cortisol (morning) | A disturbed stress-hormone rhythm can go together with poor sleep maintenance | An evening decline is normal; deviations belong with a doctor |
If you want to view these values together, a broad test such as the complete metabolic panel covers your thyroid, glucose and liver in one go. If you mainly suspect your thyroid, a targeted thyroid function test makes more sense.
What the individual values tell you
The thyroid is the thermostat of your metabolism. With an overactive thyroid your body runs at too high a pace, which can cause palpitations and trouble falling asleep. Read more about TSH and free T4 to see what the values mean.
Iron is the second one I would not skip. The storage value ferritin drops before you develop anaemia, and a low ferritin is associated with restless legs, especially in the evening. In addition, glucose and vitamin D can provide context for fatigue that will not go away.
What can you do yourself for better sleep?
Before thinking about blood, it pays to get the basics in order. A regular sleep rhythm, morning daylight and less screen time before bed are consistently linked to better sleep. The Nutrition Centre advises limiting alcohol and caffeine in the hours before bedtime, because both disturb sleep maintenance. The effect differs per person, so give a change at least two weeks.
My stance: lifestyle first, blood second. But if you remain tired and sleep poorly after an honest lifestyle effort, targeted testing is not a luxury but a sensible next step.
Frequently asked questions
Can a blood test solve my sleep problem?
No. A blood test does not measure sleep. It can show or rule out treatable physical causes, such as a thyroid or iron problem, so you can move forward more precisely.
Does fatigue always go with poor sleep?
Not necessarily. If you stay tired despite enough sleep, another cause may be at play. Discuss this with your GP, certainly with additional complaints.
Which value do I check first?
When in doubt, thyroid (TSH) and iron (ferritin) are the two that most often explain something in practice. A doctor can help decide what is useful in your situation.
The bottom line
With long-lasting sleep complaints it pays to have your thyroid and iron checked, alongside getting your lifestyle in order. Every blood test result at Vitalcheck includes a professional review by a BIG-registered doctor. A blood value is not a diagnosis: always discuss treatment decisions with your GP. To dig deeper into fatigue, read why am I so tired or the pillar on burnout and your body.
Sources
- NHG guideline Sleep problems and sleeping pills. Dutch College of General Practitioners.
- Voedingscentrum (Netherlands Nutrition Centre). Sleep, nutrition, caffeine and alcohol. Accessed 2026.
- Gezondheidsraad (Health Council of the Netherlands). Movement guidelines and daylight. Accessed 2026.
- Thuisarts.nl / NHG. I sleep badly. Accessed 2026.
الكاتب
