What Is Fatigue? What Causes Fatigue?

Fatigue, also referred to as tiredness, exhaustion, lethargy, and listlessness, describes a physical and/or mental state of being tired and weak. Although physical and mental fatigue are different, the two often exist together - if a person is physically exhausted for long enough, they will also be mentally tired. When somebody experiences physical fatigue, it means they cannot continue functioning at their normal levels of physical ability. Mental fatigue, however, is more slanted towards feeling sleepy and being unable to concentrate properly.

Fatigue is a symptom, rather than a sign. A symptom is something the patient feels and describes, such as a headache or dizziness, while a sign is something the doctor can detect without talking to the patient, such as a rash. Fatigue is a non-specific symptom, i.e. it may have several possible causes.

Mental and physical fatigue

Physical fatigue - the person's muscles cannot do things as easily as they used to. Climbing stairs or carrying laden supermarket bags may be much harder than before. Physical fatigue is also known as muscle weakness, weakness, or lack of strength. Doctors usually carry out a strength test as they go about diagnosing and trying to find out the causes of individual cases of physical fatigue.

Psychological (mental) fatigue - concentrating on things has become harder. When symptoms are severe the patient might not want to get out of bed in the morning, or perform his/her daily activities. Mental fatigue often appears together with physical fatigue in patients, but not always. People may feel sleepy, have a decreased level of consciousness, and in some cases show signs similar to that of an intoxicated state. Mental fatigue may be life threatening, especially when the sufferer has to perform some tasks, such as driving a vehicle or operating heavy machinery. Fatigue among training doctors is a serious public health concern; both for the health of the junior doctor and patients under their responsibility.

Fatigue is common

Young woman suffering with fatigue
Fatigue can affect people at any age

Experts say that 10% of people globally at any one time are suffering from persistent tiredness. Persistent tiredness affects females more than males. Primary care physicians (GPs, general practitioners) in the USA and UK say they frequently see patients who come in complaining of extreme tiredness or fatigue.

The National Institutes of Health, USA, informs that approximately one in every five Americans claims to have fatigue that is severe enough to interfere with daily normal life. More cases of fatigue have a mental than physical cause, according to collected data.

Fatigue can also affect healthy individuals after intense mental and/or physical activity.

British researchers found that undiagnosed chronic fatigue syndrome may be the reason why nearly 1% of non-truant children miss extended time off school.

What is the difference between fatigue and sleepiness?

Fatigue is usually a more chronic (long-term) condition than somnolence (sleepiness). Sleepiness is generally caused by not enough proper, restful sleep, or a lack of stimulation. Sleepiness can be a symptom of a medical condition. Fatigue, especially chronic fatigue, is usually linked to a greater medical problem.

People who suffer from fatigue feel they lack motivation and energy. Even though fatigue and drowsiness are not the same, drowsiness, or the desire to sleep, is a common symptom that accompanies fatigue. Apathy may also accompany fatigue.

According to Medilexicon's medical dictionaryFatigue is:

"1. That state, following a period of mental or bodily activity, characterized by a lessened capacity or motivation for work and reduced efficiency of accomplishment, usually accompanied by a feeling of weariness, sleepiness, irritability, or loss of ambition; may also supervene when, from any cause, energy expenditure outstrips restorative processes and may be confined to a single organ.

2. Sensation of boredom and lassitude due to absence of stimulation, monotony, or lack of interest in one's surroundings."

What are the signs and symptoms of fatigue?

The main symptom of fatigue is exhaustion (severe fatigue) after a physical or mental activity. The patient does not feel refreshed after resting or sleeping. Severe fatigue may undermine the person's ability to carry out their usual activities.

Patients describe fatigue, especially chronic fatigue (chronic fatigue syndrome) as overwhelming, and describe the tiredness as completely different from what they have experienced before - not a result of overdoing things, but simply a loss of motivation. Fatigue is a common symptom among people with clinical depression.

Some people find symptoms get worse after exercise - known as post-exertional malaise, or payback. Sometimes post-exertional malaise may not emerge until several hours after the exercise; sometimes even a day later.

Fatigue signs and symptoms may be of a physical, mental or emotional nature. Below is a list of some more possible signs and symptoms:

  • Bloating, abdominal pain, constipationdiarrhea, nausea, possibly problems similar to IBS (irritable bowel syndrome)
  • Aching or sore muscles
  • Painful lymph nodes
  • Apathy, lack of motivation
  • Chronic (long-term) tiredness
  • Difficulty in concentrating
  • Dizziness
  • Hallucinations
  • Hand-to-eye coordination may be impaired
  • Headache
  • Impaired judgment
  • Indecisiveness
  • Irritability
  • Loss of appetite
  • Moodiness
  • Poorer immune system function
  • Short-term memory impairment - there may be problems organizing thoughts and finding the right words to say (brain fog)
  • Sleepiness, drowsiness
  • Slow responses to stimuli
  • Slower-than-normal reflexes
  • Some vision problems, such as blurriness

What are the causes of fatigue?

The possible causes of fatigue are virtually endless. Most diseases listed in medical literature include malaise or fatigue as one of the potential symptoms. Causes are sometimes classified under several lifestyle problems and/or some broad disease entities.

Below are some (by no means all) possible causes of fatigue:

    • Mental health (psychiatric) - grief (bereavement), eating disorders, alcohol abuse, drug abuse, anxiety, moving home, boredom, and divorce.A certain amount of stress can invigorate us, in fact, most of us need some kind of mental pressure to get going. However, when stress levels become excessive, they can easily cause fatigue. Stress and worry are two emotions that commonly cause tiredness. Stress can reach a point in which the sufferer flounders and is "unable to see the light at the end of the tunnel", which leads them towards despair. Despair is draining, and will eventually cause fatigue if it is present for long enough. Not being in control over a situation can be frustrating, annoying, and very tiring.

      Having a baby in the house, especially if he/she wakes up a lot during the night, can interfere with the parents' sleep.

      Clinical depression can cause tiredness for several reasons. Fatigue may be caused by the depression itself, or one of the problems associated with depression, such asinsomnia.


    • Endocrine/Metabolic - Cushing's disease, kidney disease, electrolyte problems,diabeteshypothyroidismanemia, kidney disease, and liver disease.


    • Drugs/Medications - some antidepressants, antihypertensives, steroids, antihistamines, medication withdrawal, sedatives, and anti-anxiety drugs.Statin medications are among the most widely used prescription drugs sold worldwide. Researchers from the University of California, San Diego, published a report in Archives of Internal Medicine showing that statins can cause fatigue.



    • Sleep problems - working till late at night, jet lag, sleep apnea, narcolepsy, insomnia, and reflux esophagitis.Some jobs are more closely linked to a risk of fatigue than others. Examples include the police, doctors, nurses, firefighters, and shift-workers in general whose sleep patterns are "unnatural" for humans. The problem of fatigue is exacerbated if the shift-routines are regularly changed.



    • Chemicals and substances - vitamin deficiencies, mineral deficiencies, poisoning.Consuming too many caffeinated or alcoholic beverages may make it harder to get to sleep, or stay asleep, especially if you drink them close to bedtime.


Changes in neuronal structure interactions - a Swiss scientist demonstrated that there is an association between muscle fatigue and changes in the interaction between neuronal structures.

Fatigue can become self-perpetuating. An individual who feels tired may not exercise; lack of exercise can cause fatigue. Also, lack of exercise may eventually make it harder and more tiring to perform a physical chore.

Overweight and underweight - overweight/obesity is a rapidly growing problem in much of the world today. Obese people are much more likely to experience fatigue, for various reasons - having to carry a lot of weight is tiring, obese people are have a higher risk of developing diseases and conditions where fatigue is a common symptom, such as diabetes and sleep apnea. Being underweight may mean there is less muscle strength; the very thin person may tire more easily.

Diagnosing fatigue

As fatigue is present in so many diseases, conditions, states, lifestyles and syndromes, and may be caused by a vast array of factors which are usually working in combination, diagnosis can be extremely challenging.

The doctor may carry out the following diagnostic procedures and tests:

    • Evaluating the qualities of the fatigue itself - if the patient can identify the patterns of their fatigue, for example, at what times of day symptoms are worse and/or better, whether symptoms gradually worsen during the day, and whether taking a nap helps, the doctor is more likely to come to an accurate diagnosis.As sleep is known to be a major contributor to fatigue, the doctor will try to evaluate the quality of the patient's sleep, their emotional state, sleep patterns and stress levels. Total hours slept each day, and how often the person awakens during sleep are important pieces of information for the doctor during his/her evaluation.


    • Medical history and current illnesses - the patient will be asked about any recent events which are known to cause fatigue, such as giving birth, having undergone surgery, a bereavement, etc. The physician will also check for any existing illnesses and which medications the patient is currently on.


    • Lifestyle - the patient may be asked some questions regarding lifestyle, diet, alcohol consumption, illegal drug consumption, etc.


    • Physical examination - the doctor will look out for signs of illness.


  • Diagnostic tests - these will include urine tests, x-rays, possibly some other imaging scans (depending on what the doctor suspects may be the cause), blood tests, etc. It is important to try to rule out any physical causes, such as an infection, hormonal problems, anemia, liver problems, or kidney problems. The physician may order a sleep study to rule out a sleeping disorder.

If an illness is diagnosed, such as diabetes, then that illness will be treated. Well controlled diabetes will usually solve the fatigue problem. The same applies to most other illnesses and conditions.

An international team of scientists found that the spinal fluid of people with Chronic Fatigue Syndrome has a different "fingerprint" compared to that found in healthy individuals.

On average, experts say that approximately 50% of those with fatigue receive a diagnosis that could explain the condition after the patient has been affected for 12 months. Among them, 19.4% had a musculoskeletal cause, 16.5% were suffering because of psychological problems. In only 8.2% were definitive physical conditions found.

What are the treatment options for fatigue?

The successful treatment of fatigue requires finding the underlying causes and treating them. Below are some examples:



    • Blood sugar - medications to regulate blood sugar levels


    • Underactive thyroid - targeted drugs


    • Antibiotics - infections


  • Obesity - a diet and exercise regime

CBT and GET - research carried out by a team at the Medical Research Council and the UK government found that CBT (cognitive behavioral therapy) and GET (graded exercise therapy) are the most effective way of treating patients with ME (Myalgic Encephalomyelitis) or CFS (Chronic Fatigue Syndrome).

Retirement reduces fatigue - a team from Stockholm University, Sweden, reported in theBMJ (British Medical Journal) that the risk of fatigue and depression is reduced after retirement, while the chances of developing other illnesses and conditions, such as diabetes, heart disease and respiratory disease remain the same.

Multiple Sclerosis - patients responded well to mindfulness medication training for their fatigue and depression symptoms. Dr. Paul Grossman, Department of Psychosomatic Medicine, in the Division of Internal Medicine at the University of Basel Hospital, Switzerland, found that compared to those on standard medical care, the patients who learned mindfulness medication had fewer and less severe fatigue symptoms.

Yoga has been shown in various studies to help alleviate the symptoms of fatigue

Yoga - cancer survivors who completed a four-week yoga program which covered postures, meditation, breathing, and some other techniques reported significant improvements in fatigue symptoms as well as sleep quality. The researchers, from the University of Rochester Medical Center in New York, said that patients reported taking less sleep medications and improved quality of life.

Ginseng - a two-month course of high-dose American ginseng (Panax quinquefolius) reduced fatigue symptoms in cancer patients significantly more effectively than a placebo, Mayo Clinic doctors reported.

What you can do yourself to overcome persistent fatigue


  • Try to go to bed and wake up at the same time each day
  • Set your bedroom's temperature at a comfortable level. It must neither be too cold nor too hot
  • Do not have your last meal of the day too close to your bedtime - not less than 90 minutes or two hours before you go to bed
  • As bedtime approaches, physically and mentally slow down. Have a warm bath and listen to some soothing music. Clear your mind of stressful and worrying thoughts.
  • Many patients have found keeping a diary helps.

Eating and drinking habits

Physical activity

Remember that fatigue-physical inactivity-fatigue vicious cycle. If you are unfit you are more likely to feel tired. Break that cycle. It is important that any physical activity drive is done properly and gradually. Either talk to your doctor, ask an expert at a reputable gym, or see a sports scientists.

Regular exercisers sleep better and suffer much less from fatigue than other people.

If none of these steps help you, see your doctor.

Donating blood - in 2010, the International Blood Bank association urged all its members toadvise people with chronic fatigue syndrome not to donate blood and blood components, because of the risk of passing on the virus that is thought to cause the condition, even though there is no clear link for such a risk.

Written by Christian Nordqvist

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