Why am I always tired? Deficiencies and other causes

Often the cause is ordinary: too little sleep or poor sleep, stress, low mood, too little movement, poor food, or a lot of caffeine or alcohol. But constant tiredness can also come from things a doctor can find with a few questions and tests, including iron deficiency and anemia, low vitamin B12 or vitamin D, an underactive thyroid, sleep apnea and depression. Healthdirect Australia advises seeing a doctor if fatigue lasts more than two weeks and is not getting better, and sooner if it is worrying you, stopping you from doing things, or comes with other symptoms such as weight loss.

This page is general information, not a diagnosis. I have kept it to what health services and studies say is worth ruling out, and how soon.

The ordinary causes come first#

The NHS lists not getting enough sleep or finding it hard to sleep, an unhealthy lifestyle with a poor diet and little exercise, stress, depression and hard life events among the common causes. Healthdirect adds a busy schedule, too much caffeine, excessive alcohol and other substances, and notes that some medicines cause fatigue.

Daylight may belong on the list too. In more than 400,000 UK Biobank participants, each extra hour spent outdoors in daylight was associated with less frequent tiredness, easier getting up and fewer insomnia symptoms. That is a correlation, not proof, but going outside costs nothing to try.

These are the first things to fix, and the other energy articles take them one at a time, starting with sleep and food. They matter here for a particular reason: tiredness is one of the loudest inside cues, and low energy makes the old habit louder.

If the basics are in order and the tiredness stays, the causes below are the ones to ask a doctor about.

Medical causes worth ruling out#

Iron deficiency and anemia#

The WHO considers iron deficiency the most common nutritional deficiency leading to anemia, and anemia causes fatigue, lower capacity for physical work and shortness of breath. It estimates that 30% of women aged 15 to 49, 37% of pregnant women and 40% of children aged 6 to 59 months have anemia worldwide.

The NHS lists tiredness and lack of energy, shortness of breath, noticeable heartbeats and paler than usual skin among the symptoms. Heavy periods and pregnancy are very common causes. Bleeding in the stomach and intestines is another common one, which is a reason the cause needs finding, not just the iron replacing. A blood test makes the diagnosis.

How common it is depends on where you live and who you are:

• India. The national family health survey of 2019–21 found 57% of women and 25% of men aged 15 to 49 were anemic, up from 53% and 23% in 2015–16.
• The US. In national survey data from 2003 to 2020, 38.6% of females aged 12 to 21 were iron deficient and 6.3% had iron-deficiency anemia. Most who were iron deficient were not anemic, which is why the authors argue that checking for anemia alone misses many.

Do not take iron without a test. Guessing leaves the real cause unfound, and too much iron does harm. High-dose iron supplements can cause stomach upset, constipation, nausea and vomiting, and the US upper limit for adults is 45 mg a day. The NHS says 17 mg a day or less is unlikely to cause harm, and higher doses are for when a doctor advises them. Some people absorb too much iron already: hemochromatosis is an inherited condition in which iron slowly builds up over years, most often in people of white northern European background. And iron is dangerous to children. The US Food and Drug Administration requires iron supplements sold as tablets or capsules to carry a warning that accidental overdose is a leading cause of fatal poisoning in children under 6.

Vitamin B12#

B12 occurs naturally only in animal foods, so vegans, and vegetarians who eat some dairy or eggs, are at higher risk, although fortified foods and supplements reduce it. Older adults are at risk too: depending on the definition used, between 3% and 43% of older adults living in the community are deficient, especially those with atrophic gastritis, a stomach condition that reduces absorption. Others at risk include people with pernicious anemia, an autoimmune condition that the NHS calls the most common cause of B12 deficiency in the UK, people with gut conditions such as celiac disease or after stomach surgery, and people taking acid-reducing medicines (proton pump inhibitors and H2 blockers) or metformin. If you take one of these, do not stop it. Ask the prescriber whether your B12 should be checked.

The NHS lists extreme tiredness, a lack of energy, pins and needles, a sore red tongue, mouth ulcers, muscle weakness, problems with vision, problems with memory, understanding and judgment, and mood changes ranging from mild depression or anxiety to confusion. It says diagnosis and treatment should come as soon as possible, because some of the problems can become permanent.

Vitamin D#

In pooled European surveys of 55,844 people, 13% had levels below 30 nmol/L across the year, and 17.7% of those tested from October to March. In one small trial of 120 tired adults who were also deficient, treatment eased fatigue more than placebo. Who is at risk, region by region, is in sunlight and vitamin D.

An underactive thyroid#

The NHS lists feeling extremely tired, putting on weight, low mood or depression, feeling cold more than usual, and dry skin, dry hair or hair loss. Anyone can develop it; the NHS notes that Hashimoto's disease, one of its causes, is most common in women and usually starts between the ages of 30 and 50. A blood test finds it.

Sleep apnea#

Breathing stops and starts during sleep, with gasping, snorting or choking noises, waking up a lot and loud snoring. In the day it shows as feeling very tired, finding it hard to concentrate, mood swings and headaches on waking. If someone shares your room, ask them what they hear. One 2019 analysis estimated that 936 million adults aged 30 to 69 worldwide have at least mild obstructive sleep apnea by sleep-test criteria, and 425 million have moderate to severe. The NHS says it can be serious if it is not diagnosed and treated, and in the UK, at least, it can affect whether you are allowed to drive.

Low mood and depression#

Lack of energy and disturbed sleep are among the physical symptoms of depression the NHS lists, alongside continuous low mood, losing interest or enjoyment, and feeling hopeless. Its advice is to see a doctor if the symptoms last most of the day, every day, for more than two weeks.

Other causes a doctor will think about#

Healthdirect also lists diabetes, infections such as flu, COVID-19 and glandular fever, heart failure and other heart conditions, kidney disease, some autoimmune conditions and cancer. They are part of why a doctor asks about other symptoms before deciding what to test.

When to see a doctor, and how soon#

See a doctor if you have been tired for more than two weeks and it is not getting better, or for a few weeks and you are not sure why. Go sooner if it is stopping you from doing things, or comes with other symptoms such as weight loss or a change in mood. With breathlessness, some signs need emergency help straight away: severe difficulty breathing, a chest that feels tight or heavy, pain spreading to the arms, back, neck and jaw, lips or skin turning very pale, blue or gray, or sudden confusion. For any of those, call your local emergency number.

It helps to bring a short note: how long it has lasted, the hours you sleep and whether you snore, what you eat (especially if you eat no meat or no animal foods), whether your periods are heavy, every medicine and supplement you take, and how your mood has been.

Questions people ask#

Can a vitamin deficiency make you tired?#

Yes. Tiredness and lack of energy are listed symptoms of iron deficiency anemia and of B12 deficiency, and in one small trial, treating low vitamin D in tired adults eased their fatigue.

Should I take iron or a multivitamin just in case?#

Not iron, and not high-dose vitamins, without a test and a doctor's advice. Upper limits exist because more can do harm: 45 mg a day for iron in the US guidance, and 100 micrograms a day for vitamin D.

Why am I tired even after a full night's sleep?#

Hours are not the same as rest. Sleep apnea stops and starts breathing through the night and wakes people again and again, and low mood, anemia and an underactive thyroid all cause tiredness of their own. Those are questions for a doctor.

When the body is short of something, everything is harder, including staying stopped. Finding and fixing a deficiency can take away one of the reasons the evenings feel heavy, but it is not a fix for the habit. The habit is stopped the way it always is: once, completely, with the cues taken away or caught early. Thirty days is the plan, and the tests can happen in the same month.