Seven medical reasons for feeling tired

Could fatigue be a sign of an underlying health condition?

Updated: 
one sad woman sitting on the floor near a wall and holding her head in her hands

We all get tired from time to time, but if you constantly feel lethargic, it could be a sign of something more serious. Here are seven health conditions known to cause fatigue.

See also: These every day sleep aids could have deadly consequences

See also: The surprising foods that help you fall asleep


1. Anaemia
Iron-deficiency anaemia is one of the most common cause of tiredness. It affects around 1 in 20 men and postmenopausal women, and is even more common in women who have heavy periods. Symptoms include a lack of energy, shortness of breath, heart palpitations, heavy feeling muscles and a pale complexion.

While iron deficiency anaemia is the most common type, other types of anaemia can be caused by a lack of vitamin B12 or folate in the body. Your doctor will be able to confirm with a blood test.

Depending on the cause of your anaemia, your doctor can prescribe iron tablets. Eating more iron-rich foods may also help – good choices are dark-green leafy vegetables, meat, fish, eggs, iron-fortified cereals or bread, brown rice, pulses and beans, nuts and seeds, and dried fruit, like raisins, dried apricots, and prunes.

2. Sleep apnoea
Sleep apnoea is a common condition that is most likely to affect overweight middle-aged men. It's caused by the throat narrowing or closing during sleep, which repeatedly interrupts your breathing. People with obstructive sleep apnoea (OSA) snore loudly and may wake up with a gasp many times during the night. Those with the condition don't always know they have it – the only symptom may be daytime sleepiness.

Because sleep apnoea is associated with an increased risk of heart attack and stroke, it's important to see your GP. Your doctor may suggest lifestyle changes, such as losing weight, drinking less alcohol, stopping smoking, and sleeping on your side. They may also suggest that you use CPAP (continuous positive airway pressure) device. These prevent your airway closing while you sleep by delivering a continuous supply of compressed air through a mask.

3. Underactive thyroid
People with an underactive thyroid gland don't produce enough of the hormone thyroxine, which causes fatigue. The condition is more common in women, particularly as they get older. In the UK, it affects 15 in every 1,000 women and 1 in 1,000 men.

Aside from tiredness, an underactive thyroid can also cause weight gain, aching muscles and depression. Other symptoms may include dry skin and hair and sensitivity to the cold.

Your doctor can diagnose an underactive thyroid by taking a blood test. It can be treated by taking daily hormone replacement tablets, which usually have to be taken for the rest of your life.

4. Diabetes
Diabetes typically causes fatigue, along with feeling thirsty and a need to urinate more frequently. The long-term condition, which is caused by having too much sugar in the blood, can also cause weight loss and loss of muscle mass. Other symptoms can include itching around the penis or vagina, or frequent episodes of thrush, cuts or wounds that heal slowly, and blurred vision.

Your GP can diagnose diabetes with a blood test. People diagnosed with type 1 diabetes also require regular insulin injections for the rest of their life. Unlike type 1 diabetes, type 2 diabetes is often linked to being overweight. Those with type 2 diabetes are advised to lose weight and exercise, and may be prescribed tablets to help manage the condition.

5. Coeliac disease
People with coeliac disease react adversely to the gluten found in wheat products such as bread, cakes and pasta. The autoimmune condition, where the body's immune system mistakenly attacks healthy tissue, can result in tiredness, diarrhoea, constipation, abdominal pain and unexplained weight loss.

Around one in 100 people in the UK are affected, but research suggests up to 90% of them don't know they have the condition. Your GP can check if you have coeliac disease through a blood test. While there is no cure for coeliac disease, following a gluten-free diet can help to manage symptoms.

6. Glandular fever
Glandular fever is a common viral infection that typically affects teenagers and young adults. It causes extreme tiredness, a severe sore throat, swollen glands in the neck and a high temperature. While most of these symptoms usually disappear within four to six weeks, the fatigue can last for several months.

Glandular fever, also known as infectious mononucleosis or "mono", can lead to complications in rare cases. If you are concerned, see your GP.

7. Chronic fatigue syndrome
Chronic fatigue syndrome, also known as myalgic encephalomyelitis (ME), causes extreme tiredness that doesn't get better with sleep or rest. Other symptoms may include a sore throat, muscle or joint pain, and headaches.

Around 250,000 people in the UK are estimated to have CFS. It affects more women than men, particularly those in their early 20s to mid-40s. Children may also develop the condition, usually between the ages of 13 and 15.

The fatigue can be disabling in some cases, severely affecting day-to-day life. Not everyone will make a full recovery, but most people, particularly the young, tend to improve over time. Medical experts aren't sure what causes CFS. Treatment can include cognitive behavioural therapy (CBT), a structured exercise programme called graded exercise therapy, and drugs to manage pain, sickness and insomnia.