Fatigue: Definition

Fatigue is a vague feeling of being tired, weak, or exhausted. It is often a symptom of cancer when cancer is first diagnosed, or when cancer progresses. It is also the most common side effect of cancer treatment.

Some people with cancer have described fatigue as being “tired to the bones” or “hitting a wall.” Others say it is the most distressing side effect of cancer treatment. Fatigue is different for everyone, so it is important that the person who is experiencing it describe how he or she feels. Fatigue may cause decreased ability to work or do physical activity. If the person with cancer is easily distracted and unable to concentrate on mental work or activity, then he or she may have "attentional fatigue." 

Depending on its cause, fatigue can come and go or stay constant for awhile. Fatigue from chemotherapy tends to occur a few days after the treatment, peaks, and then gets better before the next treatment. Fatigue from radiation usually doesn't happen right away. It may develop over the first two to three weeks of treatment and then increase as the treatment continues. It may last three months or more after the treatment is finished. Attentional fatigue can last up to two or three years after treatment is completed.

Causes of fatigue

We currently understand some of the causes of fatigue but not all of them. Fatigue may be related to physical changes caused by cancer or its treatment (chemotherapy, biotherapy, radiotherapy, or surgery). It is reported that the fatigue people get when receiving cancer treatment is more severe than the fatigue healthy people get. In addition, this fatigue lasts longer and is not relieved by sleep.

Studies have shown that low hemoglobin is also related to fatigue. Hemoglobin carries oxygen in the blood, so if it is low, the body cells do not get as much oxygen as they need. Also, people who are not well nourished, who don't drink enough fluid and are dehydrated, or who are not able to move around much tend to have fatigue more easily. Finally, the way a person handles stress, thinks, or behaves can influence fatigue. 

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