Fatigue is one of the most common symptoms. Almost everyone knows the feeling of being exhausted, of not being able to get out of bed, or of fighting off sleep at their desk in the afternoon. Usually, the cause is obvious: too little sleep, too much stress, a demanding period. But sometimes fatigue is more persistent, cannot be remedied by sleep, and has no obvious explanation. Then it's worth taking a closer look.

The many faces of tiredness

Not all fatigue is the same. There are different forms, each with its own distinct feeling and cause. Physical fatigue manifests as heaviness in the limbs, muscle weakness, and the urge to lie down. It occurs after physical exertion, but also in some illnesses. Mental fatigue presents as difficulty concentrating, slowed thinking, and trouble formulating clear thoughts. It is typical after intense mental work or during periods of chronic stress. Emotional exhaustion is the feeling of inner emptiness, lacking energy for emotions, and becoming indifferent. It is a core symptom of burnout. Drowsiness is the urge to fall asleep and the feeling of being unable to keep one's eyes open. It differs from general exhaustion, where one is tired but not necessarily able to sleep.

When is tiredness normal?

Temporary fatigue after poor sleep, a stressful week, or a night of partying is perfectly normal. It disappears once the body has recovered, usually after one or two good nights. Some fluctuations in energy levels throughout the day are also normal – most people experience an energy slump in the early afternoon. Fatigue becomes problematic when it persists for weeks, even with sufficient sleep, when it impairs quality of life, or when it is accompanied by other symptoms.

There are many causes of persistent fatigue. Often, several factors are at play. A systematic evaluation can help identify the relevant causes.

Sleep-related causes

The most obvious cause of fatigue is insufficient or poor-quality sleep. Many people chronically sleep too little and get used to it without realizing how impaired they are. But even with sufficient sleep duration, sleep quality can suffer. Sleep apnea is widespread and underdiagnosed: pauses in breathing during sleep lead to repeated brief awakenings without those affected being consciously aware of them. The result is unrefreshing sleep despite long hours spent in bed. Restless legs syndrome causes unpleasant sensations in the legs, making it difficult to fall asleep. Insomnia, the inability to fall asleep or stay asleep, can have various causes and leads to chronic sleep deprivation.

Metabolism and hormones

Various metabolic disorders can cause fatigue. Hypothyroidism (underactive thyroid) is one of the most common hormonal causes—metabolism slows down, leading to fatigue, weight gain, and cold intolerance. Diabetes and prediabetes can be associated with fatigue, especially with fluctuating blood sugar levels. Hormonal changes during menopause or with low testosterone can also cause exhaustion. Adrenal fatigue is a controversial concept, but chronic stress can indeed deplete the stress axis and contribute to fatigue.

Nutrient deficiencies

Iron deficiency is the most common nutritional deficiency worldwide and a significant cause of fatigue, especially in women with heavy menstrual bleeding. Vitamin B12 deficiency can occur in vegetarians, vegans, and the elderly, causing fatigue and neurological symptoms. Vitamin D deficiency is common in our latitudes and can contribute to fatigue and mood problems. Magnesium deficiency can cause fatigue and muscle weakness.

Sometimes chronic fatigue is caused by a treatable condition. The diagnosis can be life-changing because the right treatment restores energy.

Infections and the immune system

Acute infections obviously cause fatigue – the body needs energy for the immune response. But chronic or low-grade infections can also lead to persistent exhaustion. Infectious mononucleosis (glandular fever) can leave you feeling tired for months. Chronic hepatitis puts a strain on the body. Chronic Fatigue Syndrome (ME/CFS) is a distinct illness characterized by profound exhaustion that is not improved by rest and worsened by activity. Long COVID has shown many people that viral infections can cause long-lasting fatigue.

Cardiovascular diseases

Heart failure leads to insufficient oxygen supply to the body, causing fatigue. Fatigue during exertion is often an early warning sign, before other symptoms appear. Anemia, or low red blood cell count, means reduced oxygen transport and therefore fatigue. The causes of anemia are varied, ranging from iron deficiency and chronic diseases to blood loss.

Mental illnesses

Depression and anxiety disorders are often accompanied by fatigue. In depression, exhaustion is often worst in the morning and improves throughout the day – the opposite of the normal pattern. Chronic stress and burnout exhaust the body and lead to profound fatigue. Distinguishing between physical and psychological causes is not always easy, and both can occur together.

Autoimmune diseases and others

Diseases such as Hashimoto's thyroiditis, rheumatoid arthritis, lupus, or multiple sclerosis can cause fatigue, often as one of the first symptoms. Cancer can also be accompanied by fatigue, which is why a tumor screening should be considered in cases of unexplained exhaustion.

Before looking for medical causes, it's worth taking an honest look at your own lifestyle. Many factors that cause fatigue are within your control.

Sleep hygiene

How much sleep do you really get? Not just lying in bed, but actually sleeping? Many people underestimate how much sleep they need and overestimate how much they actually get. Seven to nine hours are recommended for most adults, but individual needs vary. Sleep quality is just as important as duration. Factors that disrupt sleep include alcohol, which makes sleep more superficial; screen time before bed, which makes it harder to fall asleep; irregular sleep schedules; an unfavorable sleep environment with too much light, noise, or the wrong temperature; and caffeine, which can still have an effect hours before bedtime.

Lack of exercise

It sounds paradoxical, but too little exercise makes you tired. The body is designed for activity, and a lack of movement leads to a downward spiral: you're tired, you move less, and you become even more tired. Regular exercise, on the other hand, improves sleep quality, increases energy levels, and reduces stress. Even a daily walk can make a difference.

Nutrition

An unbalanced diet can cause or worsen fatigue. Significant blood sugar fluctuations from sugary meals lead to energy crashes. Inadequate nutrient intake impairs numerous bodily functions. Dehydration, even mild, can cause fatigue and difficulty concentrating. Excessive alcohol consumption disrupts sleep and puts a strain on the body. Too much caffeine can create a vicious cycle: you drink coffee to combat fatigue, which leads to poorer sleep and even greater fatigue the next day.

Stress and psychological strain

Chronic stress is one of the biggest energy drains. The constant activation of the stress response exhausts the body. Worrying, rumination, and emotional strain cost energy, even if they aren't physically demanding. Sometimes, fatigue is the body's way of signaling that something is wrong in life.

If you experience persistent fatigue without an obvious cause, a systematic investigation is advisable. A doctor's visit is the first step, but it can be helpful to know which examinations might be relevant.

Medical history and physical examination

The process begins with a detailed consultation: When did the fatigue start? How does it manifest itself? What makes it better, what makes it worse? Are there any accompanying symptoms? The physical examination can already provide clues to certain causes, such as an enlarged thyroid gland, pale mucous membranes in cases of anemia, or signs of depression.

Laboratory tests

Blood tests can reveal or rule out many causes of fatigue. A sensible basic workup includes a complete blood count to rule out anemia and signs of infection. Thyroid levels, especially TSH, as well as free T3 and free T4 if abnormal, are important. Iron, ferritin, and transferrin saturation indicate iron status. Vitamin B12 and folic acid are particularly relevant for vegans and vegetarians. Vitamin D levels are often low in our latitudes. Blood glucose and HbA1c levels rule out diabetes. Liver and kidney function tests indicate organ function. Inflammatory markers such as CRP can indicate chronic inflammation. Depending on the situation, further tests may be useful: cortisol if an adrenal gland problem is suspected, sex hormones if corresponding symptoms are present, and specific tests if certain diseases are suspected.

Further diagnostics

If sleep disorders are suspected, a sleep study (polysomnography) can be performed. For heart problems, an ECG and echocardiography are used. If depression is suspected, a psychiatric evaluation is advisable. Sometimes diagnosis requires patience – not all causes are found on the first attempt.

Since sleep is the foundation for energy, it's worth focusing on this. Even small improvements in sleep quality can have noticeable effects on energy levels.

Optimize sleep amount

Find out how much sleep you really need. You can test this by waking up without an alarm clock for a week and observing when you naturally wake up and how you feel. Most adults need seven to nine hours. Less than six hours is insufficient for almost no one in the long run, even if some people believe it is. Sleep requirements change throughout life and with circumstances – the body needs more sleep during times of stress or illness.

Improve sleep quality

Several factors are important for good sleep quality. The sleep environment should be dark, quiet, and cool, ideally between 16 and 19 degrees Celsius. The bed should be used only for sleep and intimacy, not for work or watching television. Regular sleep times, even on weekends, stabilize the circadian rhythm. An evening routine that prepares the body for sleep is helpful. Screens should be avoided for an hour before bedtime, as the blue light inhibits melatonin production. Alcohol should be limited, as it makes sleep more superficial. Caffeine should be avoided after the early afternoon.

Treating sleep disorders

If problems persist despite good sleep hygiene, a sleep disorder should be investigated. Sleep apnea is common and treatable, but often goes undetected. Insomnia can be treated with cognitive behavioral therapy, which is more effective in the long term than sleeping pills. Other sleep disorders, such as restless legs syndrome, have specific treatments.

Nutrition and exercise are two levers that everyone can control and that can have a significant impact on energy levels.

Energy-stabilizing nutrition

The goal is to have stable energy throughout the day, without the spikes and dips of blood sugar fluctuations. Complex carbohydrates from whole grains, legumes, and vegetables provide steady energy. Protein with every meal stabilizes blood sugar and promotes satiety. Healthy fats from nuts, olive oil, and oily fish support many bodily functions. Simple sugars and highly processed foods should be limited, as they lead to energy crashes. Regular meals prevent blood sugar from dropping too low. Staying hydrated is important, as dehydration causes fatigue.

Nutrients for energy

Certain nutrients are particularly important for energy metabolism. Iron is necessary for oxygen transport and is found in meat, legumes, and leafy green vegetables. B vitamins are cofactors in energy metabolism and are found in whole grains, meat, eggs, and legumes. Magnesium is involved in over 300 enzymatic reactions and is found in nuts, seeds, whole grains, and green vegetables. Coenzyme Q10 is important for cellular energy production. If a deficiency is suspected, a blood test is recommended before indiscriminately supplementing.

Movement as an energy source

Exercise requires energy in the short term, but gives back more in the long run. Regular physical activity improves mitochondrial function, i.e., energy production in the cells. It improves sleep, reduces stress, and increases physical resilience. Moderate activities such as brisk walking, cycling, or swimming are sufficient to get started. Three 30-minute sessions per week are a good beginning. Those who are already active should check whether overtraining might be a problem – too much exercise can also lead to exhaustion.

In addition to the basics – sleep, nutrition, exercise – there are strategies to better utilize available energy in everyday life and to minimize energy drainers.

Energy audit

For one week, observe when you are energetic and when you are exhausted. Are there any patterns? Most people have an energy peak in the late morning and a dip in the early afternoon. But individual patterns can vary. Schedule demanding tasks for your peak energy periods and routine tasks for your low energy periods. Don't fight your natural rhythm; use it to your advantage.

Use breaks strategically

Without breaks, productivity drops and exhaustion increases. Short breaks every 60 to 90 minutes help maintain energy levels. Effective breaks include getting up and moving around, going outside for fresh air, socializing, or doing something completely different. Ineffective breaks include scrolling through social media or checking emails. This further exhausts you without providing rest. A short power nap of 10 to 20 minutes can work wonders in the afternoon, but it shouldn't be too long, otherwise you'll experience sleep inertia.

Identify energy drainers

Certain activities, situations, or people drain a disproportionate amount of energy. Meetings that lead nowhere. Tasks that are constantly postponed and cause mental strain. Conflicts that remain unresolved. Decisions that aren't made. Identify your personal energy drains and consider how you can minimize them. Sometimes an unpleasant conversation or a difficult decision is exhausting in the short term, but relieving in the long run.

Cultivate energy sources

What gives you energy? It could be activities, people, places, or even thoughts. Consciously plan energizing activities instead of just reacting to exhaustion. For some, it's sports, for others a creative hobby, time in nature, or with certain people.

If lifestyle changes are insufficient or fatigue is particularly pronounced, a blood test can help identify or rule out physical causes. A comprehensive fatigue check examines the most common treatable causes.

Important laboratory parameters

A comprehensive fatigue assessment should include various parameters. A blood test reveals whether anemia is present, a common and easily treatable cause of fatigue. Thyroid function, particularly TSH, indicates whether the thyroid gland is functioning normally. Hypothyroidism is a common and easily treatable cause of fatigue. Iron status, measured by ferritin and, if necessary, transferrin, can be low even without overt anemia and cause fatigue. Vitamin B12 is essential for energy metabolism and nerve function; a deficiency is particularly common in plant-based diets. Vitamin D levels are frequently low in our latitudes and can contribute to fatigue and mood problems. Blood sugar and HbA1c levels indicate whether diabetes or prediabetes is present. Inflammatory markers such as CRP can point to chronic inflammation, which consumes energy.

Extended diagnostics

Depending on the situation, further tests may be useful. Cortisol indicates whether the stress axis is out of balance. In cases of chronic stress, cortisol may initially be elevated and later decreased. Sex hormones such as testosterone in men or estrogen and progesterone in women can be relevant in cases of fatigue and other symptoms. Liver and kidney function tests reflect organ function and can provide clues to various diseases.

Interpreting results

The results should always be interpreted in the context of the symptoms. A value just within the normal range can still be symptomatic, especially with iron and thyroid levels. Conversely, not every abnormal value automatically explains fatigue. Consulting a doctor is important to correctly interpret the results and, if necessary, initiate treatment.

Fatigue is a complex symptom that can have various causes – from simple lack of sleep and nutritional deficiencies to treatable illnesses. The path to more energy begins with understanding your own situation and leads through systematic changes.

Key findings

Fatigue that doesn't improve with sleep or persists for more than a few weeks should be investigated. Optimizing the basics first means: sleep quantity and quality, diet, exercise, and stress management. Many treatable causes can be identified through blood tests, including thyroid problems, iron deficiency, vitamin B12 deficiency, and vitamin D deficiency. Lifestyle factors such as lack of exercise, an unbalanced diet, and chronic stress are common and modifiable causes. Energy management means using available energy wisely and minimizing energy drainers.

Concrete next steps

Keep a sleep diary for a week: How much sleep do you actually get? How do you feel in the morning? Honestly assess your lifestyle: Are you getting enough exercise? Do you eat a balanced diet? How do you manage stress? Identify your energy drainers and energy sources. If fatigue persists: Get a blood test to rule out treatable causes. Be patient – ​​energy problems often develop over a long period and take time to improve.

An encouraging thought

Chronic fatigue is frustrating, but in most cases, there are solutions. Sometimes it's a simple deficiency that can be addressed. Sometimes it's lifestyle changes that take time but are effective. Sometimes it's an underlying medical condition that can be treated. The first step is to take the problem seriously and tackle it systematically. You deserve to feel energized—and the path to feeling that way is within reach.