Causes of Cancer Fatigue
Fatigue in people with cancer may have more than one cause.
Doctors do not know all the reasons people with cancer have fatigue. Many conditions may cause fatigue at the same time.
Fatigue in people with cancer may be caused by the following:
- Cancer treatment.
- Receiving more than one type of treatment (for example, both chemotherapy and radiation therapy).
- Anemia (a lower than normal number of red blood cells).
- Hormone levels that are too low or too high.
- Trouble breathing or getting enough oxygen.
- Infection.
- Pain and other symptoms.
- Stress.
- Problems getting enough sleep.
- Loss of appetite or not getting enough calories and nutrients.
- Dehydration (loss of too much water from the body, such as from severe diarrhea or vomiting).
- Changes in how well the body uses food for energy.
- Loss of weight, muscle, and/or strength.
- Medicines that cause drowsiness.
- Not being active.
- Being overweight.
- Tumors in certain parts of the body.
- Other medical conditions.
- Having fatigue before cancer treatment begins.
Fatigue is common in people with advanced cancer who are not receiving cancer treatment.
It is not clear how cancer treatments cause fatigue.
It is unclear how cancer treatments such as surgery, chemotherapy, and radiation therapy cause fatigue.
When cancer treatment begins, many patients are already tired from medical tests, surgery, and the emotional stress of coping with the cancer diagnosis. Fatigue may get worse during treatment.
Different cancer treatments have different effects on a patient's energy level. The type and schedule of treatments can affect the amount of fatigue caused by cancer treatment. Some patients have more fatigue after cancer treatments than others do.
Fatigue related to surgery
Fatigue is often a side effect of surgery, but patients usually feel better with time. However, fatigue related to surgery can be worse when the surgery is combined with other cancer treatments.
Fatigue caused by chemotherapy
Patients treated with chemotherapy usually feel the most fatigue in the days right after each treatment. Then the fatigue decreases until the next treatment. Some studies have shown that patients have the most severe fatigue about mid-way through all the cycles of chemotherapy. Fatigue decreases after chemotherapy is finished, but patients may not feel back to normal until a month or more after the last treatment.
Fatigue during chemotherapy may be increased by the following:
- Pain.
- Depression.
- Anxiety.
- Anemia.
- Lack of sleep caused by some anticancer drugs.
Fatigue caused by radiation therapy
Many patients receiving radiation therapy have fatigue that keeps them from being as active as they want to be. After radiation therapy begins, fatigue usually increases until mid-way through the course of treatments and then stays about the same until treatment ends. For many patients, fatigue improves after radiation therapy stops. However, in some patients, fatigue will last months or years after treatment ends.
Fatigue caused by hormone therapy
Women who are being treated with hormone therapy for breast cancer may have fatigue. Fatigue during hormone therapy may also be increased in breast cancer survivors who are younger than 55 years, overweight, or have more pain and insomnia.
Fatigue caused by immunotherapy
Immunotherapy often causes flu-like symptoms, such as fever, chills, headache, and muscle or body aches. Some patients may also have trouble thinking clearly. Fatigue symptoms depend on the type of immunotherapy used.
Anemia is a common cause of fatigue.
Some types of chemotherapy stop the bone marrow from making enough new red blood cells, causing anemia (too few red blood cells to carry oxygen to the body). Anemia affects the patient's energy level and quality of life. Anemia may be caused by the following:
- Cancer.
- Cancer treatments.
- A medical condition not related to the cancer.
Nutrition needs change and cause or increase fatigue.
For many patients, the effects of cancer and cancer treatments make it hard to eat well. The body's energy comes from food. Fatigue may occur if the body does not take in enough food to give the body the energy it needs. In people with cancer, three major factors may affect nutrition:
- A change in the way the body uses food. A patient may eat the same amount as before having cancer, but the body may not be able to absorb and use all the nutrients from the food. This is caused by the cancer or its treatment.
- An increase in the amount of energy needed by the body because of a growing tumor, infection, fever, or shortness of breath.
- A decrease in the amount of food eaten because of low appetite, nausea, vomiting, diarrhea, or a blocked bowel.
Anxiety and depression are the most common psychological causes of fatigue in people with cancer.
The emotional stress of cancer can cause physical problems, including fatigue. It's common for you to have changes in moods and attitudes. You may feel anxiety and fear before and after a cancer diagnosis. These feelings may cause fatigue. The effect of the disease on your physical, mental, social, and financial well-being can increase emotional distress.
About 15% to 25% of people with cancer get depressed, which may increase fatigue caused by physical factors. Patients who have depression before starting treatment are more likely to have depression during and after treatment. The following are signs of depression:
- Lack of energy and mental alertness.
- Loss of interest in life.
- Problems thinking.
- Drowsiness.
- Feeling a loss of hope.
Patients who have a history of stressful experiences in childhood, such as abuse and neglect, may have increased fatigue. See the PDQ summaries on Adjustment to Cancer: Anxiety and Distress and Depression for more information.
Fatigue and memory problems may be related.
During and after cancer treatment, you may find that you cannot pay attention for very long and have a hard time trying to think, remember, and understand. This is called attention fatigue. Sleep helps to relieve attention fatigue, but sleep may not be enough when the fatigue is related to cancer. Take part in restful activities and spend time outdoors to help relieve attention fatigue.
Not sleeping well causes fatigue.
Some people with cancer are not able to get enough sleep. The following problems related to sleep may cause fatigue:
- Waking up during the night.
- Going to sleep at different times every night.
- Sleeping during the day and less at night.
- Being inactive during the day.
- The time of day that cancer treatment is given.
Poor sleep affects people in different ways. For example, the time of day that fatigue is worse may be different. Some people with cancer who have trouble sleeping may feel more fatigue in the morning. Others may have severe fatigue in both the morning and the evening. People with cancer who are inactive during the day, have restless sleep, or who have obesity may have higher levels of fatigue.
Even in people with cancer who have poor sleep, fixing sleep problems does not always improve fatigue. A lack of sleep may not be the cause of the fatigue. See the PDQ summary on Sleep Disorders for more information.
Medicines other than chemotherapy may add to fatigue.
Patients may take medicines for pain or conditions other than the cancer that cause drowsiness. Opioids, antidepressants, and antihistamines have this side effect. If these medicines are taken at the same time, fatigue may be worse.
Taking opioids over time may lower the amount of sex hormones made in the testicles and ovaries. This can lead to fatigue as well as sexual problems and depression.