Sleep Disorders and Sleep Deprivation: An Unmet Public

Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem
http://www.nap.edu/catalog/11617.html
76 SLEEP DISORDERS AND SLEEP DEPRIVATION
• Causing clinically significant distress or impairment in social, occupational,
or other important areas of functioning.
• Not occurring exclusively during the course of another sleep disorder.
• Not due to the direct physiological effects of a substance or a medical
condition (APA, 1994).
Insomnia symptoms are remarkably common, affecting at least 10 percent
of adults in the United States (Ford and Kamerow, 1989; Ohayon et
al., 1997; Simon and VonKorff, 1997; Roth and Ancoli-Israel, 1999). Prevalence
is higher among women and older individuals (Mellinger et al., 1985;
Ford and Kamerow, 1989; Foley et al., 1995). Severe insomnia tends to be
chronic, with about 85 percent of patients continuing to report the same
symptoms and impairment months or years after diagnosis (Hohagen et al.,
1993; Katz and McHorney, 1998). The comorbidity of sleep disorders with
psychiatric disorders is covered later in this chapter.
Etiology and Risk Factors
The precise causes of insomnia are poorly understood but, in general
terms, involve a combination of biological, psychological, and social factors.
Insomnia is conceptualized as a state of hyperarousal (Perlis et al., 2005).
Stress is thought to play a leading role in activating the hypothalamicpituitary
axis and setting the stage for chronic insomnia. A key study showed
that adults with insomnia, compared with normal sleepers, have higher levels,
over a 24-hr period, of cortisol and adrenocorticotropic hormone (ACTH),
which are hormones released by the hypothalamic-pituitary-adrenal axis after
stress exposure (Vgontzas et al., 2001). The 24-hour pattern of cortisol
and ACTH secretion is different, however, from that in individuals who are
chronically stressed. Cognitive factors, such as worry, rumination, and fear
of sleeplessness, perpetuate the problem through behavioral conditioning.
Other perpetuating factors include light exposure and unstable sleep schedules
(Partinen and Hublin, 2005).
Insomnia patients often attribute their difficulty sleeping to an overactive
brain. Several lines of evidence, from preclinical to sleep neuroimaging
studies in insomnia patients, suggest that there are multiple neural systems
arranged hierarchically in the central nervous system that contribute to
arousal as well as insomnia complaints. Disturbances in these systems may
differ according to the nature of insomnia. Structures that regulate sleep
and wakefulness, for example the brainstem, hypothalamus and basal forebrain,
are abnormally overactive during sleep in primary insomnia patients
(Nofzinger et al., 2004b). In addition, limbic and paralimbic structures that
regulate basic emotions and instinctual behaviors such as the amygdala,
hippocampus, ventromedial prefrontal cortex and anterior cingulate cortex
Copyright © National Academy of Sciences. All rights reserved.