Why Am I Always Tired? What to Check First

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The short answer

Check sleep first, then ask a GP for the standard blood tests, then look at habits and mood. Fatigue is a main or secondary reason in 10 to 20 percent of primary care consultations¹, yet in GP patients a somatic cause is found in only 8 percent³. A normal blood test is common, not a failure, and a supplement is not the first step.

How common is feeling tired all the time?

Very common. In consultations recorded by 89 Irish GPs, fatigue appeared in 25 percent of visits: the main reason in 6.5 percent and a secondary reason in 19 percent². Reviews estimate fatigue is a main or secondary reason in 10 to 20 percent of all primary care consultations¹.

What matters most is the honest finding: among GP patients whose tiredness is explained, a somatic cause accounts for 8 percent and a psychosocial cause for 16 percent, leaving about three quarters unexplained³. Depression is the single most common identified cause at 18.5 percent, while previously undiagnosed cancer is rare at 0.6 percent and anaemia with other organic causes accounts for 4.3 percent¹. So the most likely explanations are sleep, mood and stress, not a hidden disease. That does not mean tiredness is imaginary; it means the check order should start cheap and common.

Is your sleep long enough and good enough?

Start here, because sleep problems and sleep related breathing disorders are among the most common causes of persistent fatigue¹. Before any blood test, check whether your sleep is long enough, regular, and uninterrupted. Note how often you wake, and when you have your last alcohol and caffeine, because a GP will ask about both. A 2023 guideline for family medicine recommends the history covers sleeping behaviour alongside existing conditions, drugs and psychosocial factors before any laboratory testing¹¹.

Could it be sleep apnoea?

Yes, and it is underdiagnosed. Obstructive sleep apnoea affects an estimated 3 to 7 percent of adults⁴, and a majority of those affected remain undiagnosed. Ask your partner, or record yourself: loud habitual snoring, witnessed pauses in breathing, waking with gasping or choking, unrefreshing sleep and daytime sleepiness are the classic pattern.

Diagnosis is medical. The standard is polysomnography, with an apnoea hypopnea index greater than 5 in the presence of symptoms, or greater than 15 without symptoms⁵. Sleep apnoea is a medical condition: if the pattern fits, see a doctor rather than buying anything. Diagnosis and treatment belong with a doctor or a sleep clinic.

Could low iron make you tired even without anaemia?

Low iron stores are common in tired women even when the blood count is normal. In a trial of non anaemic women aged 18 to 55 with unexplained fatigue, 51 percent had a serum ferritin of 20 µg/l or lower at the start⁶.

The practical point: a normal haemoglobin does not rule out low iron stores. Ask for ferritin, not just a full blood count. We cover this in depth in iron deficiency in women. Taking iron at the doses used in that trial is a decision to make with a doctor, after a ferritin result.

Could low vitamin B12 or folate be the cause?

Possibly, but it is not common. Vitamin B12 deficiency affects approximately 2 to 3 percent of adults in the United States⁷. Total serum B12 is diagnostic for deficiency if less than 180 pg/mL, while borderline levels of 180 to 350 pg/mL warrant a methylmalonic acid measurement⁷. Risk factors include malabsorption, limited dietary intake, metformin, proton pump inhibitors and older age, and symptoms can include fatigue, brain fog and depression⁷.

One caution from the same review: persistently elevated B12, defined as greater than the high threshold on two measurements, has been associated with serious disease, so more is not better⁷. Read more in what are the signs of low vitamin B12.

Could your thyroid be involved?

It can be, but mildly abnormal results are often not the answer. Subclinical hypothyroidism, an elevated TSH with normal free T4, affects up to 10 percent of adults⁸. In older adults, a TSH above the usual upper limit of 4 to 5 mU/L can occur without any thyroid disease⁸, so one result slightly out of range is something to discuss with a doctor, not a diagnosis.

A 2019 BMJ guideline, based on 21 trials with 2192 participants, found no clinically relevant difference in quality of life or thyroid related symptoms, tiredness included, when a mildly raised TSH was treated⁹. In people already treated for an underactive thyroid, 10 percent still feel unwell with normal test results¹⁰, which is one more reason a TSH number alone does not explain tiredness.

Which blood tests does a doctor usually order for tiredness?

A GP typically orders a small, cheap set. The German fatigue guideline recommends blood glucose, full blood count, inflammation markers, liver enzymes and TSH as basic diagnostics, with further testing only for specific indications¹¹. We explain what each marker means in which blood markers are worth checking before you supplement.

Test	What it shows	What it misses
Full blood count	Anaemia, including B12 related changes¹	Low iron stores without anaemia⁶
Ferritin	Iron stores, which can be low while the blood count is normal⁶	Thyroid, sleep and mood causes
Vitamin B12 and folate	Deficiency below 180 pg/mL; borderline 180 to 350 pg/mL needs methylmalonic acid⁷	Borderline function not yet in the blood
TSH	Overt thyroid disease; subclinical pattern up to 10 percent of adults⁸	Whether mildly high TSH explains fatigue⁹
Glucose	Diabetes as an organic cause¹¹	Most unexplained fatigue, about three quarters of GP cases³

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What everyday habits drain energy?

Stress and low mood matter more than most people expect: depression is the most common identified cause of persistent fatigue, at 18.5 percent¹. Excessive psychosocial stress sits alongside sleep disorders at the top of the cause list¹.

A two week diary of sleep times, alcohol, caffeine and activity gives a GP the information the history needs. Activity belongs in that diary too: the review advises discussing a level of exercise that suits the person¹. None of these shows up in a blood test, which is exactly why the history comes first in every guideline¹¹. If tiredness has lasted more than six months, the Dutch review advises expanding the history toward sleep and hereditary factors³.

When should tiredness send you to a doctor soon?

See a doctor promptly if tiredness comes with unintended weight loss, fever or night sweats, blood loss, shortness of breath, swollen glands, or new neurological symptoms such as numbness or loss of balance. These raise concern for conditions including undiagnosed cancer, which is rare at 0.6 percent of fatigue cases but real¹.

Also seek care soon if a partner observes pauses in breathing at night, suggesting sleep apnoea⁴, or if low mood or loss of interest dominates the picture, since depression is the most common identified cause at 18.5 percent¹. Tiredness lasting more than six months deserves an expanded evaluation by a GP regardless³.

What can supplements do for tiredness, and what can they not do?

Less than marketing suggests. A supplement cannot treat sleep apnoea, depression, stress or any medical cause, and it is not a substitute for finding the cause first.

What supplements can legitimately do is support nutrient intake. Under the authorised EU claims, riboflavin, niacin, pantothenic acid, vitamin B6, folate and vitamin B12 contribute to the reduction of tiredness and fatigue, which is why some people choose a B complex with active forms when dietary intake is low. Magnesium carries the same authorised claim for the reduction of tiredness and fatigue, and our combined magnesium product provides 251 mg of elemental magnesium per daily serving. Neither product replaces finding the cause, and neither is meant for a diagnosed deficiency.

Frequently Asked Questions

Why are my blood tests normal even though I am exhausted?

Because that is the usual outcome. In GP patients with fatigue, a somatic cause is found in only 8 percent and about three quarters remain unexplained³. Normal tests point the search toward sleep, habits, stress and mood rather than away from any real problem.

Which test shows low iron without anaemia?

Serum ferritin. It measures iron stores, while a full blood count can look normal when those stores are low. In one trial of non anaemic women with unexplained fatigue, 51 percent had a ferritin at or below 20 µg/l⁶.

Should I take iron just in case?

No. Iron is a decision for after a ferritin result, made with a doctor. A ferritin test tells you whether iron is the question at all⁶.

Is a slightly high TSH making me tired?

Probably not by itself. Subclinical hypothyroidism affects up to 10 percent of adults⁸, and a review of 21 trials found no clinically relevant difference in fatigue when it was treated⁹. Ask your doctor how to read your own result.

How common is sleep apnoea as a hidden cause?

Obstructive sleep apnoea affects 3 to 7 percent of adults and most cases are undiagnosed⁴. Loud snoring with witnessed breathing pauses and daytime sleepiness is the pattern to check with a doctor⁵.

What does a B vitamin supplement do, and what does it not do?

Not by itself. B vitamins carry the authorised claim that they contribute to the reduction of tiredness and fatigue, which means supporting normal function when intake is low, not treating a cause. If B12 deficiency is possible, testing is the first step, with deficiency defined below 180 pg/mL⁷.

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The Bottom Line

Work through the check order rather than the supplement shelf: sleep quality including possible sleep apnoea, then a small set of GP blood tests with ferritin, B12 and TSH, then alcohol, caffeine, activity, stress and mood. Remember the honest numbers: only 8 percent of GP fatigue has a somatic cause and 16 percent a psychosocial one, leaving about three quarters unexplained³, with depression the most common identified cause at 18.5 percent¹. A normal result is information, not a dead end, and no supplement is a promised fix.

Why Am I Always Tired? What to Check First

The short answer

How common is feeling tired all the time?