Always tired? The everyday reasons behind chronic fatigue – and what the research says

You wake up tired. You get through the morning on coffee. By three o'clock, you would trade almost anything for 20 minutes on the sofa.

Then the weekend comes, and it doesn't fix it.

Most of us know what ordinary tiredness feels like. It follows a late night or a hard week, and it eases with rest. Persistent fatigue is different. It can last for weeks or months, and a good night's sleep doesn't put it right.

It is also a common reason for seeing a doctor. Sometimes the tests come back normal. That can be reassuring and frustrating at the same time.

Tiredness is a symptom, not a diagnosis

Fatigue has many possible causes. Often there isn't one neat explanation.

It is usually a combination: too little sleep, a stressful period that never quite ends, irregular meals and, perhaps, a deficiency or another health problem underneath.

In our clinic, we rarely find a single cause. More often, it is two or three things that together drain your energy.

So where do you start?

1. Sleep: not just how long, but how well

Sleep is the obvious place to look. It is also the one we most often underestimate.

Short nights add up. But you can also spend eight hours in bed and wake up feeling as though you have barely slept. Snoring, pauses in breathing, waking in the night, alcohol in the evening or a bedroom that is too warm can all break up your sleep.

If you sleep enough but still wake up exhausted, the useful question isn't how to sleep longer. It is: why is your sleep not restorative?

In our clinic, poor sleep is one of the threads we come across most often. It is rarely the whole story on its own.

2. Stress: when "on" never switches off

Stress is useful in short bursts. The problem comes when there is no chance to switch off and recover.

Long periods of stress can affect your sleep, appetite, mood, and energy. Some people describe feeling "wired but tired": exhausted all day, then wide awake the moment they get into bed.

Recovery is part of the answer, not an extra. It can be as simple as a proper lunch break, a walk without your phone, or an hour between work and bed.

3. Food: what you eat, and when

When you eat may matter as much as what you eat.

A 2026 Swedish study looked at 485 girls aged 15 to 19. Those who skipped breakfast or school lunch reported more fatigue and a lower quality of life. So did those who used nicotine every day.

The study can't tell us whether skipping meals caused the fatigue. Tiredness may also make it harder to eat regularly. But it fits with what many people notice in daily life.

Long gaps between meals can make energy and concentration less steady. A mid-afternoon slump isn't always about lunch. Sometimes it is about the breakfast you didn't have.

4. Blood values: important, but not the whole story

Low iron stores, low vitamin B12, thyroid problems, and unstable blood sugar can all cause tiredness. That is one reason a blood test is useful when tiredness doesn't go away.

But the research is more nuanced than "low iron equals tired".

In the Swedish study, more than a third of the girls had iron deficiency. Yet iron deficiency alone was not linked to how tired they felt. Heavy periods, skipped meals and nicotine use were more clearly linked. Our take? You need a personalised approach - someone who looks at you, your lifestyle, and your numbers - and figures out why you are tired.

A separate 2026 study of 228 adults in Turkey found something slightly different. People with more fatigue had lower ferritin (iron stores) and lower haemoglobin. Their vitamin D levels were not linked to fatigue.

Both studies were cross-sectional. They show links at one point in time, not cause and effect. But they make an important point: a single blood value rarely tells the whole story.

In our clinic, we start with how you feel, and read your results with that in mind.

5. Periods: often overlooked

Heavy periods are common. Many women have lived with them for so long that they no longer see them as unusual.

In the Swedish study, heavy periods were one of the factors most clearly linked to fatigue, even when other factors were considered.

If your periods are very heavy, last longer than a week, or mean you need to change protection very often, talk to a doctor or nurse. Heavy bleeding can also lower your iron stores over time.

6. Supplements: less magic than the packaging suggests

When you are tired, it is tempting to look for an answer in a bottle.

A 2026 review looked at 27 studies of NAD+ supplements, such as NMN and NADH. These are often sold for energy and healthy ageing. NAD+ improved physical or mental performance in a few studies. None clearly improved how tired people felt.

That doesn't mean supplements are useless. If you are low in iron or vitamin B12, treating it can make a real difference. But treating a known deficiency is not the same as taking a supplement and hoping it fixes tiredness no one has explained.

In our clinic, we would rather measure than guess before suggesting a supplement.

When to see a doctor

See a doctor if your tiredness doesn't go away, especially if it is new, getting worse, or comes with other symptoms. These include unexplained weight loss, fever, night sweats, breathlessness, low mood or very heavy periods.

If physical or mental effort makes your symptoms much worse, sometimes a day or more later, tell your doctor. That pattern matters when working out what is going on.

So where do you start?

Probably not everywhere at once.

Start with the basics: when you sleep, when you eat, and how much recovery you get each week. If you are still tired, look at whether there is a medical or nutritional reason.

A blood test can tell you a lot. It tells you more together with your symptoms and the context.

At Wellth, we look at your blood values alongside how you sleep, eat, move, and feel. We look at the pattern, not each number on its own, and what it means for you.

You can take a blood test through Wellth or upload results you already have from another laboratory.

If you're tired of being tired, get in touch.

Contact us

Sources

• Stubbendorff A, Borgfors A, Bolmsjö BB, Vinge F, Midlöv P, Wolff M, et al. Fatigue in adolescent girls is linked to heavy menstrual bleeding, meal skipping and nicotine use – not iron deficiency. Acta Psychologica. 2026;269:107568. doi:10.1016/j.actpsy.2026.107568
• Tiril SM, Emir S, Tiril NE. Association of serum 25-hydroxyvitamin D levels with fatigue severity in adults: a cross-sectional study. North Clin Istanb. 2026;13(3):288–293. PMID: 42516797.
• Gao Y, Li S, Guan J, et al. Domain-specific effects of NAD+ precursors on fatigue and functional performance: a systematic review and network meta-analysis. Frontiers in Nutrition. 2026. doi:10.3389/fnut.2026.1890335