Always Tired? Understanding the Causes of Persistent Fatigue

Do you wake up tired after a full night's sleep, or find everyday tasks unusually exhausting? Occasional tiredness after a demanding day is normal. When fatigue lasts, keeps returning or gets in the way of daily life, it is worth finding the cause.

What is fatigue?

Fatigue is a persistent feeling of tiredness or reduced energy that does not improve adequately with rest. It helps to separate it from two related symptoms:

• Fatigue: physical or mental exhaustion.
• Sleepiness: a tendency to fall asleep, especially during quiet activities. This points more towards a sleep problem.
• Muscle weakness: reduced strength, or difficulty with movements that used to be easy.

What are the most common causes of persistent fatigue?

Causes range from everyday habits to medical conditions, and more than one may be involved.[1]

1. Too little sleep, or poor-quality sleep

Adults generally need at least seven hours a night.[3] Late nights, shift work, screens at bedtime, alcohol and frequent waking all take a toll. Obstructive sleep apnoea, where breathing repeatedly stops during sleep, can cause loud snoring, gasping, morning headaches and daytime sleepiness, even if you do not remember waking.[4]

2. Iron deficiency and anaemia

Iron is needed to make haemoglobin, which carries oxygen in the blood. When iron deficiency causes anaemia, it can bring fatigue, breathlessness on exertion, dizziness, palpitations and pale skin.[5] Heavy periods, gastrointestinal blood loss and poor absorption raise the risk. Not every iron deficiency causes anaemia, and not every anaemia is due to iron, so blood tests are needed to tell them apart.

Important: unnecessary iron supplements can be harmful, and the reason for a deficiency may itself need investigating.[6]

3. Vitamin B12 deficiency

B12 supports red blood cell formation and nerve function. A deficiency can cause fatigue, and sometimes numbness, tingling, balance problems or memory changes. People on vegan diets without a reliable B12 source, people with some digestive disorders, and those taking certain long-term medicines such as metformin are at higher risk.[7]

4. Thyroid disorders

An underactive thyroid (hypothyroidism) can cause tiredness, feeling cold, constipation, dry skin, weight gain, poor concentration and menstrual changes.[8] An overactive thyroid can also cause fatigue, often with palpitations, tremor, heat intolerance or weight loss. A TSH blood test, sometimes with free T4, checks thyroid function.

5. Diabetes

Diabetes can develop gradually. When symptoms appear, they may include thirst, frequent urination, weight loss, blurred vision and fatigue.[9] Fatigue alone does not mean you have diabetes, but with these symptoms or risk factors a glucose or HbA1c test is sensible. Read more in our guide to type 2 diabetes.

6. Stress, anxiety and depression

Prolonged stress is mentally exhausting, anxiety disrupts sleep, and depression can cause persistent fatigue with loss of interest and changes in sleep or appetite.[10] These symptoms are real and are not laziness. They also do not rule out a physical cause, so a good assessment considers both. See also when stress shows up in the body.

7. Medicines

Some antihistamines, sedatives, sleeping tablets and other medicines can cause drowsiness or fatigue. If tiredness started after a new medicine or dose change, tell your prescriber, but do not stop a prescribed medicine abruptly.

8. Other conditions

Infections, chronic inflammatory conditions, kidney disease and heart disease can also cause fatigue.[1] Which is most likely depends on your history and examination.

Why am I always tired even after sleeping?

The usual explanations are poor sleep quality, sleep apnoea, a thyroid or other medical condition, depression or prolonged stress, or a medicine side effect. If this keeps happening, talk to a doctor rather than relying on more caffeine or supplements.

What tests may be needed for persistent fatigue?

A general physician may suggest some of these when your symptoms point to them:[1]

Not everyone needs every test. Ordering large panels without a reason adds cost and can produce confusing results, so a targeted approach is usually more useful. Your doctor will also ask about sleep, diet, activity, medicines, periods, recent infections and mood.

How can you improve your energy levels?

• Keep a regular sleep schedule. Same bedtime and wake time, a dark and quiet room, and less caffeine later in the day.
• Eat balanced, regular meals. Vegetables, fruit, whole grains, pulses, nuts and protein. If you are vegetarian or vegan, pay attention to B12 and iron.
• Stay active. Start with short walks and build up gradually.[11] If fatigue comes with chest pain, breathlessness or fainting, see a doctor before strenuous exercise.
• Look after your mental well-being. Breaks, realistic workloads and support from others help. Seek help for persistent low mood or anxiety.
• Do not lean on caffeine. Needing more and more to function is a sign to look for the underlying cause.

When should you see a doctor for fatigue?

Book a consultation if your fatigue:

• has lasted several weeks without a clear reason
• interferes with work, study or daily life
• comes with weight change, persistent fever or night sweats
• comes with increased thirst or frequent urination
• comes with heavy periods, or numbness, tingling or balance problems
• began after a medicine change and has not improved

Frequently asked questions

Can vitamin deficiency cause constant tiredness?

Yes. Iron and vitamin B12 deficiency can both cause fatigue.[5][7] Many other conditions cause similar symptoms, so testing should follow a clinical assessment.

What blood tests should I get if I am always tired?

There is no single panel that suits everyone. Depending on your symptoms, a doctor may suggest a CBC, thyroid tests, glucose, iron studies or B12.[1]

Can I treat fatigue with supplements?

Supplements help when a specific deficiency is present. They are unlikely to fix fatigue with another cause, and unnecessary supplements can be harmful.[6]

Understand the cause before treating the symptom

Persistent fatigue has many explanations, from poor sleep and stress to anaemia, thyroid problems and diabetes. Finding what is behind it works better than assuming exhaustion is just part of a busy life.

Related reading: diabetes, BP and thyroid care, common health concerns, your HbA1c report, explained, type 2 diabetes explained, and getting the most from a consultation.