Q. I was recently diagnosed with depression. It turns out that depression has likely caused the fatigue I've been unable to shake for the past few months. What's the connection between the two?
A. Everybody experiences fatigue now and then. Yet some people suffer from constant fatigue. There are literally hundreds of different diseases that cause a chronic state of fatigue.
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What is fatigue? It's a sensation of sleepiness, muscle weakness, or a feeling that you don't have the energy to do something -- either physical or mental. It's the brain that experiences fatigue; that means there are certain chemical changes in the brain that lead to fatigue -- even though those chemical changes may be triggered by many different illnesses.
According to published studies, as many as 20 percent to 40 percent of people who seek a doctor's help for fatigue are suffering from depression. Unfortunately, there is also a lot of evidence that doctors don't always recognize depression -- particularly when a patient does not express sadness, just fatigue.
One hallmark of depression is a decreased drive or motivation to do things that you once enjoyed. Another is a change in sleep patterns; some people sleep more than usual, others develop insomnia. Still others start waking up unusually early in the morning, like 4 or 5 a.m.
People with anxiety, on the other hand, are prone to panic, fear and other high-stress responses. These cause fatigue by increasing levels of stress hormones. These people are also more likely to have chronic high-stress reactions -- the most debilitating and energy-robbing kind. Many people with anxiety also suffer from depression.
Getting help for depression and anxiety is extremely important. Treatment will improve your mood, and it should also help get your energy level back to where it once was.
Several therapies, including medication and psychotherapy, can relieve the symptoms of depression. Lifestyle changes, such as exercise, also help.
Medication: Antidepressants work by adjusting levels of brain chemicals that play a role in depression. Selective serotonin reuptake inhibitors (SSRIs) increase the brain's level of serotonin, which affects mood, arousal, anxiety, impulses and aggression. SSRIs are the most commonly prescribed medicines for depression.
Tricyclic antidepressants are an older class of medication. They increase brain chemicals that affect mood, anxiety and drive. These drugs are often the best choice if you have trouble sleeping.
Psychotherapy: Therapy with a psychiatrist, psychologist or social worker can also help treat depression. Combining psychotherapy with an antidepressant is often effective.
Exercise: A sustained exercise program can improve your mood if you have mild or moderate depression. It can also increase your energy level.
Anxiety can be treated with medications, psychotherapy or both. Cognitive behavioral therapy is especially helpful.
So in answer to your question, fatigue is a common manifestation of depression. Why depression is linked to fatigue, and what causes depression in the first place, remain mysterious. Many research scientists are spending their lives trying to find answers to those questions.
• Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com.