Causes of Fatigue in Cancer Patients
Key Points for This Section
- Fatigue in cancer patients may have more than one cause.
- How cancer treatments cause fatigue is not known.
- Anemia is a common cause of fatigue.
- Side effects related to nutrition may cause or increase fatigue.
- Anxiety and depression are the most common psychological causes of fatigue in cancer patients.
- Fatigue may be increased when it is hard for patients to learn and remember.
- Not sleeping well may cause fatigue.
- Medicines other than chemotherapy may add to fatigue.
Fatigue in cancer patients may be caused by the following:
- Cancer treatment with chemotherapy, radiation therapy, and some biologic therapies.
- 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.
- Heart trouble.
- 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.
- Problems getting enough sleep.
- Being less active.
- Other medical conditions.
Fatigue is common in people with advanced cancer who are not receiving cancer treatment.
Doctors are trying to better understand how cancer treatments such as surgery, chemotherapy, and radiation therapy cause fatigue. Some studies show that fatigue is caused by:
- The need for extra energy to repair and heal body tissue damaged by treatment.
- The build-up of toxic substances that are left in the body after cells are killed by cancer treatment.
- The effect of biologic therapy on the immune system.
- Changes in the body's sleep-wake cycle.
When they begin cancer treatment, many patients are already tired from medical tests, surgery, and the emotional stress of coping with the cancer diagnosis. After treatment begins, fatigue may get worse. Patients who are older, have advanced cancer, or receive more than one type of treatment (for example, both chemotherapy and radiation therapy) are more likely to have long-term fatigue.
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 therapy.
Patients treated with chemotherapy usually feel the most fatigue in the days right after each treatment. Then the fatigue decreases until the next treatment. Fatigue usually increases with each cycle. 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. Many patients feel fatigued for months or years after treatment ends.
Fatigue during chemotherapy may be increased by the following:
- Anemia. 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).
- Lack of sleep caused by some anticancer drugs.
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. Some patients never have the same amount of energy they had before treatment.
Cancer-related fatigue has been studied in patients with breast cancer and prostate cancer. The amount of fatigue they felt and the time of day the fatigue was worst was different in different patients.
In men with prostate cancer, fatigue was increased by having the following symptoms before radiation therapy started:
- Poor sleep.
In women with breast cancer, fatigue was increased by the following:
- Working while receiving radiation therapy.
- Having children at home.
- Trouble sleeping.
- Younger age.
- Being underweight.
- Having advanced cancer or other medical conditions.
Biologic therapy often causes flu-like symptoms. These symptoms include being tired physically and mentally, fever, chills, muscle pain, headache, and not feeling well in general. Some patients may also have problems thinking clearly. Fatigue symptoms depend on the type of biologic therapy used.
Fatigue is often a side effect of surgery, but patients usually feel better with time. However, fatigue caused by surgery can be worse when the surgery is combined with other cancer treatments.
Anemia affects the patient's energy level and quality of life. Anemia may be caused by the following:
- The cancer.
- Cancer treatments.
- A medical condition not related to the cancer.
The effects of anemia on a patient depend on the following:
- How quickly the anemia occurs.
- The patient's age.
- The amount of plasma (fluid part of the blood) in the patient's blood.
- Other medical conditions the patient has.
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. For many patients, the effects of cancer and cancer treatments make it hard to eat well. In people with cancer, three major factors may affect nutrition:
- A change in the way the body is able to use 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.
- A decrease in the amount of food eaten because of low appetite, nausea, vomiting, diarrhea, or a blocked bowel.
- An increase in the amount of energy needed by the body because of a growing tumor, infection, fever, or shortness of breath.
The emotional stress of cancer can cause physical problems, including fatigue. It's common for cancer patients to have changes in moods and attitudes. Patients may feel anxiety and fear before and after a cancer diagnosis. These feelings may cause fatigue. The effect of the disease on the patient's physical, mental, social, and financial well-being can increase emotional distress.
About 15% to 25% of patients who have cancer get depressed, which may increase fatigue caused by physical factors. The following are signs of depression:
- Feeling tired mentally and physically.
- Loss of interest in life.
- Problems thinking.
- Loss of sleep.
- Feeling a loss of hope.
Some patients have more fatigue after cancer treatments than others do.
During and after cancer treatment, patients may find they cannot pay attention for very long and have a hard time thinking, remembering, and understanding. This is called attention fatigue. Sleep helps to relieve attention fatigue, but sleep may not be enough when the fatigue is related to cancer. Taking part in restful activities and spending time outdoors may help relieve attention 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.
- Not going to sleep at the same time every night.
- Sleeping during the day and less at night.
- Not being active during the day.
Poor sleep affects people in different ways. For example, the time of day that fatigue is worse may be different. Some patients who have trouble sleeping may feel more fatigue in the morning. Others may have severe fatigue in both the morning and the evening.
Even in patients 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.
Patients may take medicines for cancer symptoms, such as pain, or conditions other than the cancer. These medicines may cause the patient to feel sleepy. Opioids, antidepressants, and antihistamines have this side effect. If many of these medicines are taken at the same time, fatigue may be worse.