Person about to have a cup of coffee for fatigue

Fatigue Explained: Causes and More

Table of contents

Fatigue can reduce your quality of life—and make every day feel exhausting.

But what is fatigue?

Fatigue means a feeling of tiredness that often makes it difficult to carry out normal activities [1]. People can experience both physical and mental fatigue [2].

Physically, fatigue can include a feeling of slowness or sluggishness, lowered physical endurance, and greater difficulty carrying out physical tasks. Mentally, fatigue can make it harder to concentrate, result in slowed thinking, and decrease motivation [3].

There are many factors that can affect your energy level, such as a B vitamin deficiency, hormone imbalance, or your sleep habits.

Causes of Fatigue

Some common causes of fatigue are:

  • Vitamin deficiencies - Low levels of vitamins like B9 and B12 are known to cause fatigue [4, 5]. Anyone can become deficient in these vitamins, but the risk of B12 deficiency increases with age [6]. Because B12 is rare in plant foods, vegetarians and vegans are also at risk of deficiency—unless B12-fortified foods are regularly eaten or supplements are used. People with malabsorption syndromes like celiac disease are especially at risk of B9 deficiency [4] because these syndromes make it difficult for B9 to be absorbed into the bloodstream and circulated throughout the body.
  • Thyroid disorders - An underactive thyroid—a condition known as hypothyroidism—can slow down your metabolism, making you feel tired [7]. Hypothyroidism occurs when your thyroid gland doesn’t make enough thyroid hormones. In the U.S., Hashimoto’s disease—a kind of immune system malfunction—is the main cause of hypothyroidism. Test thyroid hormones from the comfort of home.
  • Adrenal insufficiency - The adrenal glands are responsible for pumping out hormones like cortisol during stressful moments, which gives you a rush of energy. If you have adrenal insufficiency, however, your adrenal glands fail to provide your body with enough cortisol. In some cases, adrenal insufficiency can result in fatigue [8]. Adrenal insufficiency commonly results when you abruptly stop taking corticosteroids (a type of medication used to treat inflammation) after using them for a while. Immune system malfunction is another common cause of adrenal insufficiency [9].
  • Sleep disorders - Your body has a 24-hour “clock”—or sleep-wake cycle—that helps you fall asleep at night and wake up in the morning. But too much exposure to light at night can disrupt the balance of hormones that regulate your body’s “clock,” resulting in daytime tiredness or insomnia [10]. Other sleep disorders, like sleep apnea, can also lead to fatigue [11]. Sleep apnea is caused by problems with muscles involved in breathing. Obesity, a family history of sleep apnea, and smoking are all risk factors for this condition.
  • Inflammatory diseases - Chronic fatigue is very common among people with inflammatory diseases like rheumatoid arthritis [12], which is caused by an immune system malfunction. Cigarette smoking is one of the main risk factors for rheumatoid arthritis [13].
  • Cancer - Cancer causes extreme fatigue in many cases [14]. What’s more, cancer-related fatigue often worsens during cancer treatment [15]. Cancer can occur as a result of many different factors, including exposure to radiation, certain viruses, and some kinds of chemicals (such as those found in tobacco smoke) [16].

Some of the top health conditions connected with fatigue include:

  • Hypothyroidism (underactive thyroid)
  • Anemia (lack of healthy red blood cells, which can be caused by B vitamin deficiencies)
  • Sleep disorders (like sleep apnea and circadian rhythm sleep disorders)
  • Cancer
  • Adrenal insufficiency (a condition that occurs when the adrenal glands don’t produce enough hormones like cortisol)
  • Diabetes
  • Fibromyalgia (a condition that causes pain throughout the body and often includes symptoms fatigue and memory problems)
  • Liver and kidney disease
  • Chronic fatigue syndrome
  • Depression
  • Anxiety

When to Get Medical Care for Fatigue

It’s normal to occasionally experience some fatigue. If you stayed up late last night binge watching your favorite show, you might feel sluggish the next day.

However, fatigue that doesn’t go away after 2 or more weeks can be a sign that something more serious is at play—so scheduling an appointment with your healthcare provider is a good idea [17].

Ways to Reduce Fatigue

Treat Yourself to Good Sleep Habits

Getting a restful night of sleep often comes down to what you do before you hit the pillow. Regularly practicing good before-bed habits can help you sleep better—and wake up feeling refreshed.

Try practicing habits like these [18]:

  • Avoid drinking alcohol and coffee (or having other stimulants, like nicotine) 4-6 hours before you go to bed
  • Avoid eating heavy meals and spicy foods before bedtime
  • Exercise during the day instead of just before you go to bed
  • Make sure your bedroom is a quiet, dark place—and that it’s not too hot or too cold!
  • Only go to bed when you feel tired, and get back up out of bed if you’re unable to fall asleep
  • Try to get up at the same time every morning

Consider Taking a Supplement

A supplement like melatonin may be worth considering as a tool to help regulate your sleep-wake cycle. (Melatonin exists naturally in your body as a hormone that helps promote sleep.)

Melatonin supplements can be especially useful for resetting your body’s sleep “clock” if you experience jet lag or an irregular sleep cycle because of shift work.

Note: It’s always a good idea to talk to your healthcare provider about any supplements you’re taking or are considering taking—and remember that supplements do vary in quality, so be sure you’ve checked the source.

Common Questions About Fatigue

What Is Chronic Fatigue Syndrome?

People who have ongoing fatigue for more than 6 months may be experiencing chronic fatigue syndrome (CFS). This health condition often includes symptoms like impaired memory or concentration, sore throats, muscle pain, headaches, and unrefreshing sleep [19, 20].

What Causes Fatigue?

Many different health conditions can cause fatigue—from nutritional deficiencies and hormone imbalances to chronic diseases like cancer. Determining the cause of fatigue isn’t always easy, but lab tests can help—so consider trying an Everlywell at-home lab test that measures markers connected to fatigue.

Why Am I Tired All the Time?

Thyroid Fatigue: Key Points to Know

Can Allergies Make You Tired? How to Manage Allergy Fatigue and Sleep Better


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