Causes of cancer fatigue

Cancer fatigue may be caused by many factors, and the factors that contribute to your cancer fatigue may be completely different from those of someone else. However, possible contributing factors include:

• Your cancer. Your cancer can cause changes to your body that can lead to fatigue. For instance, some cancers release proteins called cytokines, which are thought to cause fatigue.

  Other cancers can increase your body's need for energy, weaken your muscles, cause damage to certain organs (such as liver, kidney, heart or lungs) or alter your body's hormones, all of which may contribute to fatigue.

• Cancer treatment. Chemotherapy, radiation therapy, surgery, bone marrow transplantation and immunotherapy may all cause fatigue. You may experience fatigue if cancer treatment damages healthy cells in addition to the cancer cells. Or fatigue might happen as your body works to repair damage caused by treatment.

  Some treatment side effects — such as anemia, nausea, vomiting, pain, insomnia and changes in mood — also may cause fatigue.

• Anemia. You might develop anemia if your treatment destroys too many healthy red blood cells. You can also develop anemia if the cancer has spread to your bone marrow and interferes with blood cell production or causes you to lose blood.
• Pain. If you experience chronic pain, you may be less active, eat less, sleep less and become depressed, all of which may add to your fatigue.
• Emotions. Anxiety, stress or depression associated with your cancer diagnosis also may lead to fatigue.
• Lack of sleep. If you're sleeping less at night or if your sleep is frequently interrupted, you may experience fatigue.
• Poor nutrition. In order to work efficiently, your body needs the energy that a healthy diet provides. When you have cancer, your body may need more nutrients than usual. But it can be hard to take in enough nutrients if treatment side effects, such as nausea and vomiting, make it difficult to eat.
• Medications. Certain medications, such as pain relievers, can cause fatigue.
• Lack of exercise. If you're used to being on the go, slowing down can make you feel fatigued.
• Hormonal changes. Hormone therapy is a common cancer treatment that causes changes in the body's hormone levels that can lead to significant fatigue. Hormonal changes may also occur as side effects of other cancer treatments.

Not everyone who has cancer experiences fatigue. And if you do, the level of cancer fatigue you experience can vary — you may feel a mild lack of energy, or you may feel completely wiped out.

Your cancer fatigue may occur episodically and last just a short while, or it may last for several months after you complete treatment.