Tiredness is one of the commonest reasons people ask for help with their health, so what turns up has been counted. Across 26 sets of findings on people who did, anaemia explained it in 2.8%. Cancer explained it in 0.6%. Some other serious physical illness, 4.3%. Depression, 18.5%. And serious physical illness turned up no more often in the tired than in people who were not tired at all.
Two things follow. A hidden cause is the exception, so the dark theory you have built about your tiredness is probably wrong. And the exception is real. A few per cent of a large number is a great many people, and each cause leaves clues.
This article is the list of clues.
Ahead: the iron shortage a normal blood count misses, why a "borderline" thyroid is rarely the answer, the test that only works while you still eat bread, the question that narrows it down faster than any test, and the remedies to stop paying for.
Tired and fatigued are two things
Tiredness answers to sleep. Fatigue does not.
The ordinary kind is short-lived. A late night, a long flight, a hard week: you sleep, you recover, it goes. Fatigue stays. Waking after eight hours feeling no different from when you lay down is fatigue, and it means the trouble sits somewhere sleep cannot reach.
If rest fixes it, you were tired, and this is the wrong article. If weeks of decent sleep change nothing, read on.
1. Low iron, with a normal blood count
A standard blood count measures the red cells in your blood. It says nothing about ferritin, the iron you hold in store, and the store can run low long before the count drops. "Anaemia" is Greek for "without blood". Low stores are the stage before it, with the blood still looking fine.
That matters, because low stores are enough to tire you. Tired women with low iron stores but normal blood counts felt their fatigue drop by almost half over twelve weeks of iron, against under a third on a dummy pill. Across four tests and 714 people who were low in iron without being anaemic, iron eased tiredness. It did nothing for how they performed on exercise tests, so the gain is in how you feel.
Clues: breathlessness, a heartbeat you can feel, paler skin than usual and, less often, more hair than usual left in the brush. Two stranger ones: legs that will not keep still at night, and wanting to chew ice. The people most likely to run low are women with heavy periods, pregnant women and frequent blood donors.
Test: ferritin, alongside a full blood count. One catch: ferritin rises with inflammation, so a normal figure during an infection can hide a low store.
Low iron needs a reason. Heavy periods and pregnancy are the common ones, and heavy periods can be treated, which fixes the leak as well as the store. Where neither applies, blood being lost in the stomach or gut is another common cause, and ibuprofen and aspirin are among the things that do it. So low iron with no obvious reason is something to have looked into, never only topped up.
Two more things. Meat, fish and poultry carry haem iron, which the body absorbs better than the iron in plants and fortified flour. And iron is one to test for, never to guess at: too much does harm, and a large amount can kill a child.
2. A slow thyroid
An underactive thyroid slows everything, and tiredness rarely arrives alone. It brings feeling cold when nobody else is, weight gain, constipation, dry skin and hair, a low mood and slow thinking. The person wearing an extra layer when no one else needs one is describing it. Its commonest cause is most common in women and usually starts between 30 and 50, and a thyroid condition in the family raises the odds. An overactive thyroid tires people too, and its company is the opposite: restlessness, nerves and irritability.
Test: a blood test for the thyroid hormones.
Here is the part the internet gets backwards. A result that is only slightly off, with the main hormone still in range, goes by "borderline" or "subclinical", and it gets blamed for a great deal of tiredness. When 737 older adults with a borderline result were given thyroid hormone or a dummy tablet for a year, their tiredness ended up the same. Across 21 tests and 2,192 adults, treating a borderline thyroid brought no gain in symptoms or in quality of life.
So a properly slow thyroid is a cause worth finding. A borderline one is seldom your answer, and the search should go on. If you already take thyroid tablets, none of this is a reason to stop them.
3. Too little B12
Tiredness and weakness are signs of running short of B12. It is low in about 6% of people under 60 and about 20% of those over it.
B12 comes from meat, fish, eggs and dairy, so a low-carb, keto or carnivore plate has it covered. The body's stores last two to five years, so a shortage creeps up slowly, sometimes years after the change that caused it. People who eat no animal foods and take no B12 are the obvious group. For them a supplement is the fix, and carries NSF's contents certification, which means an outside lab checked the bottle against the label. The less obvious one is on tablets: more on that below.
The severe kind of B12 shortage used to be called pernicious anaemia, and "pernicious" means deadly. It earned the name: before there was a treatment, people lasted one to three years. Around 1926 it was found that eating liver turned it round.
Clues: pins and needles, a sore red tongue, mouth ulcers, and trouble with memory.
Test: a blood level of B12.
4. Too little vitamin D
One hundred and twenty tired adults who were low in vitamin D were given either a single large amount of it or a dummy. Four weeks on, fatigue had eased in 72% of the first group against 50% of the second.
Everyone in that test was low to begin with, and that is the point. Vitamin D helps the person who is short of it. More is no better: too much from a bottle over a long time builds up calcium and can damage the kidneys and the heart. Your skin makes it from sunlight, and in a northern winter there is too little sun to go on. Oily fish is one of the few foods that carry it, and a tin of brings B12 along as well.
Clues: a dark winter behind you, a life spent indoors, skin that is always covered, or dark skin, which makes less vitamin D from the same sunlight.
Test: 25-hydroxy vitamin D, the form that is measured in blood.
5. Sleep apnoea
This is the cause that hides inside sleep itself. In sleep apnoea the airway keeps closing during the night. The sleeper keeps half-waking to breathe, often with no idea it is happening, and gets up after eight hours feeling wrecked. It is common: by one estimate about 936 million adults between 30 and 69 have it, 425 million of them at a moderate or severe level.
"Apnoea" is Greek for "absence of breathing". Dickens drew the picture long before the word was used for it: Joe, "the fat boy" in The Pickwick Papers, who falls asleep in the middle of everything.
Clues: loud snoring, gasping, snorting or choking noises in the night, a headache on waking, and feeling worn out through the day. The best witness is whoever shares your bed.
Test: a sleep test, done at home or in a clinic. No supplement reaches a mechanical problem in the airway. Untreated, it raises the chance of a serious accident from tiredness, a car crash among them, so this is one to chase.
6. Diabetes
Heavy tiredness is one of the commonest signs of type 2 diabetes. Its company gives it away: thirst that never lets up, peeing more than usual, and losing weight without trying.
Test: a blood test for blood sugar.
7. Coeliac disease
In coeliac disease the gut reacts to gluten and stops absorbing food properly, and tiredness is one of its signs. It affects at least 1 person in 100, and milder cases often go unrecognised.
Gluten was caught by a famine. In the Dutch hunger winter of 1944 to 1945 bread ran out, and the death rate among children with coeliac disease fell from over 35% to almost nothing. When the wheat came back, so did the deaths.
Clues: bloating, stomach aches, diarrhoea or constipation, weight loss, and low iron that nobody can explain. It runs in families: the parents, brothers, sisters and children of someone who has it are at higher risk and should be tested.
Test: a blood test, and here is the trap. It only works while you are still eating gluten. Go gluten-free first "to see if it helps" and you can hide the thing you are looking for.
8. Low mood
Go back to the numbers at the top. Depression was the commonest finding by a distance, in nearly one tired person in five. A lack of energy is one of its physical signs, along with disturbed sleep and a changed appetite.
Clue: the tiredness comes with a flat mood and no pleasure in things you used to like. If that has been there most of the day, every day, for more than two weeks, reach out for help.
9. A medicine
Some tablets tire you directly. Tiredness is a common side effect of beta blockers, the tablets given for blood pressure and the heart, and one whole group of antihistamines is known for making people sleepy.
Others do it slowly, through a nutrient. Metformin, the common diabetes tablet, counts B12 deficiency among its common side effects. Long-term acid-reducing tablets can pull B12 down too.
Try this: list everything you take, and ask whether any of it could be behind the tiredness. Keep taking it while you ask.
When did it start?
This question narrows the list faster than any test. Write the answer down, in a or on the back of an envelope, and take it with you when you get checked.
After an infection. Glandular fever can leave tiredness that lasts for months.
During pregnancy, or after it. Pregnancy is one of the commonest causes of low iron. Check ferritin first.
In your forties, with your periods changing. In perimenopause, the years leading up to the menopause, bleeding can get heavier, which drains iron, and night sweats break up sleep.
After a change of diet. Cutting out animal foods lowers the supply of B12 and of the iron that absorbs best. Because B12 stores last for years, the tiredness can arrive long after the change.
At the end of a hard year. Long strain wears people down without help from any deficiency. Look at mood first, then at rest.
The caffeine mask
Caffeine gives the feeling of energy without supplying any. It blocks the brain's receptors for adenosine, the chemical that builds up through the day and signals fatigue. The signal is still there. You have stopped hearing it.
In daily drinkers, the morning cup mostly undoes the tiredness and low mood that a night without caffeine has built. So coffee makes this whole search harder: it hides the signal you are trying to read.
Take the mask off and expect a few rough days: tiredness and a headache that start within a day and are over in two to nine. Judge your energy after that.
The nightcap
Alcohol plays the opposite trick. At every amount tested, it got people to sleep faster and then broke up the second half of the night. A nightcap is a loan against the morning.
What to stop paying for
The baking-soda burp test for "low stomach acid". Nothing supports it.
"Functional" ranges that turn a normal result into a deficiency.
Vinegar or acid capsules before meals to "restore absorption".
Epsom-salt baths for magnesium. Reviewers who went through the evidence called the claims for magnesium through the skin "scientifically unsupported". Enjoy the bath.
The "acid load" story, in which food slowly drains your minerals.
When to go further
Get it checked if you have been tired for a few weeks with no reason you can name, if the tiredness is affecting your daily life, or if it comes with weight loss, a change in mood, or gasping and choking in your sleep.
One condition needs separate mention. In ME/CFS, also called chronic fatigue syndrome, symptoms get worse after physical or mental effort and can take weeks to settle. Pushing through is the wrong rule there.
Where to start
Answer the question first: when did it start, and what was going on? Then a second one: what runs in the family? Families share a table as well as their genes, so the answer can be a plate, a coffee pot or a bedtime as easily as a thyroid. Then read the clues above and see which fit.
Then ask for the tests that match: a full blood count and ferritin, B12, the thyroid hormones, blood sugar, vitamin D, and the coeliac test if your gut or your iron points that way. Ask for the numbers as well as the verdict. And stop one supplement first: biotin, sold for hair, skin and nails, can throw off blood tests for thyroid hormones and vitamin D in either direction. Leave it out for a few days before the blood is taken.
Fix what is low, and stop there. Give it time: iron took twelve weeks in the test above.
For most tired people the results come back clean, as the numbers at the top promised. That is an answer too. It crosses off the frightening possibilities and sends you back to the ordinary ones. Two places to look next: the room and the breath, in How to Boost Energy Levels Naturally: Little-Known Remedies That Actually Work, and how your brain reads effort, in Unstoppable Energy: 14 Ways to Stay Focused and Strong Every Day.
Start by writing down when it began.
Not sure which test to ask for? Nutrient Deficiencies: Who's at Risk and Which Test to Get — who runs low on what, and the test that shows it.
Results clean, and still worn out? Why You're Always Tired: The Rest You're Missing — the rest that sleep, workouts and clean eating leave out, and how to get it.
Know someone who has been "just tired" for a year? Send them this, and ask them when it started.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional. If your mood has been low for weeks or you're having thoughts of harming yourself, reach out for help today.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
Sources
Stadje R, Dornieden K, Baum E, et al. (2016). The differential diagnosis of tiredness: a systematic review. BMC Family Practice 17(1):147. doi.org/10.1186/s12875-016-0545-5
NHS. Iron deficiency anaemia. nhs.uk
Wiktionary. anemia. en.wiktionary.org
Vaucher P, Druais PL, Waldvogel S, Favrat B (2012). Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. Canadian Medical Association Journal 184(11):1247–1254. doi.org/10.1503/cmaj.110950
Houston BL, Hurrie D, Graham J, et al. (2018). Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults: a systematic review of randomised controlled trials. BMJ Open 8(4):e019240. doi.org/10.1136/bmjopen-2017-019240
National Institutes of Health, Office of Dietary Supplements. Iron: Fact Sheet for Health Professionals. ods.od.nih.gov
Wikipedia. Ferritin. en.wikipedia.org
NHS. Iron. nhs.uk
NHS. Underactive thyroid (hypothyroidism). nhs.uk
NHS. Tiredness and fatigue. nhs.uk
Stott DJ, Rodondi N, Kearney PM, et al. (2017). Thyroid Hormone Therapy for Older Adults with Subclinical Hypothyroidism. New England Journal of Medicine 376(26):2534–2544. doi.org/10.1056/NEJMoa1603825
Feller M, Snel M, Moutzouri E, et al. (2018). Association of Thyroid Hormone Therapy With Quality of Life and Thyroid-Related Symptoms in Patients With Subclinical Hypothyroidism. JAMA 320(13):1349–1359. doi.org/10.1001/jama.2018.13770
NHS. Vitamin B12 or folate deficiency anaemia: symptoms. nhs.uk
Wikipedia. Vitamin B12 deficiency. en.wikipedia.org
NHS. B vitamins and folic acid. nhs.uk
NHS. Vitamin B12 or folate deficiency anaemia: causes. nhs.uk
Wikipedia. Pernicious anemia. en.wikipedia.org
Nowak A, Boesch L, Andres E, et al. (2016). Effect of vitamin D3 on self-perceived fatigue. Medicine 95(52):e5353. doi.org/10.1097/MD.0000000000005353
NHS. Vitamin D. nhs.uk
NHS. Sleep apnoea. nhs.uk
Benjafield AV, Ayas NT, Eastwood PR, et al. (2019). Estimation of the global prevalence and burden of obstructive sleep apnoea: a literature-based analysis. The Lancet Respiratory Medicine 7(8):687–698. doi.org/10.1016/S2213-2600(19)30198-5
Wiktionary. apnea. en.wiktionary.org
Wikipedia. Sleep apnea. en.wikipedia.org
NHS. Type 2 diabetes: symptoms. nhs.uk
NHS. Coeliac disease. nhs.uk
Wikipedia. Coeliac disease. en.wikipedia.org
NHS. Coeliac disease: diagnosis. nhs.uk
NHS. Depression in adults: symptoms. nhs.uk
NHS. Beta blockers. nhs.uk
NHS. Antihistamines. nhs.uk
NHS. Metformin. nhs.uk
NHS. Omeprazole. nhs.uk
NHS. Glandular fever. nhs.uk
NHS. Menopause and perimenopause: symptoms. nhs.uk
Wikipedia. Caffeine. en.wikipedia.org
James JE, Rogers PJ (2005). Effects of caffeine on performance and mood: withdrawal reversal is the most plausible explanation. Psychopharmacology 182(1):1–8. doi.org/10.1007/s00213-005-0084-6
Juliano LM, Griffiths RR (2004). A critical review of caffeine withdrawal: empirical validation of symptoms and signs, incidence, severity, and associated features. Psychopharmacology 176(1):1–29. doi.org/10.1007/s00213-004-2000-x
Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB (2013). Alcohol and Sleep I: Effects on Normal Sleep. Alcoholism: Clinical and Experimental Research 37(4):539–549. doi.org/10.1111/acer.12006
Gröber U, Werner T, Vormann J, Kisters K (2017). Myth or reality—transdermal magnesium? Nutrients 9(8):813. doi.org/10.3390/nu9080813
NHS. Myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS). nhs.uk
Wikipedia. Biotin. en.wikipedia.org