Causes of Chronic Insomnia
Sleep problems seem to run in families. About 35% of people with insomnia have a family history of insomnia, with the mother being the most commonly affected family member. Still, because so many factors are involved in insomnia, a genetic component is difficult to define.
Brain Chemicals and Hormones Affecting Chronic Insomnia
Abnormal levels of certain brain chemicals have been observed in some people with chronic insomnia.
- Melatonin. Low levels of melatonin, the hormone secreted by the pineal gland, have sometimes been observed in chronic insomnia.
- Stress Hormones. Some studies have reported persistently high levels of stress hormones, particularly cortisol, in people with chronic insomnia, particularly insomnia related to aging and psychiatric disorders. High levels of cortisol reduce REM sleep. However, a 2003 study of people with chronic insomnia reported that cortisol levels were high only when their sleep was of poor quality. When they slept well, levels were lower. This study and other research suggests that high levels of stress hormones are caused by poor sleep, rather than being the cause.
- Growth Hormone. Normal aging is associated with a blunting of regular, cyclical surges of growth hormone, which may affect sleep as one gets older. This hormone, which is normally secreted in the late night, is associated not only with growth but with deep, slow-wave sleep. (Older people generally have less slow-wave sleep.)
Chronic Insomnia and the Immune System
Chronic insomnia occurs in people who have persistently high levels of stress hormones and a shift in the levels of certain immune factors. Studies indicate that people with chronic insomnia have higher levels of interleukin-6 and tumor necrosis factor during the day, but lower levels at night. These immune factors, called cytokines, cause symptoms of fatigue. Levels are usually higher at night in people with healthy sleep. The implications of these immune changes in people with insomnia are not known.
Emotional Disorders
Many cases of chronic insomnia cases have a psychologic or psychiatric basis. The disorders that most often cause insomnia are:
- Anxiety
- Depression; sleep abnormalities are an integral part of depressive disorders, with more than 90% of depressed patients experiencing insomnia
- Bipolar disorder
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