17 Other potential causes of associated insomnia include concomitant medical conditions (e.g., infections and metabolic diseases) and the use of substances or medications (e.g., alcohol, stimulants, and antidepressants). 17, 20 – 23 This form of insomnia may also be caused by inadequate sleep hygiene (i.e., habits that are inappropriate for good quality of sleep), such as psychologically stressful activities the consumption of caffeine, nicotine, alcohol, or heavy meals or vigorous physical activity near bedtime. 13Īssociated insomnia is primarily related to an underlying mental or mood disorder, such as depression, dysthymia, cyclothymia, bipolar disorder, anxiety, or schizophrenia. 12, 14, 17 – 19 Precipitating and perpetuating factors, such as psychosocial features (e.g., fatigue and irritability), behavioral changes, and cognitive characteristics, also contribute to insomnia. Primary chronic insomnia may be caused by several predisposing (genetic and constitutional) factors, including hyperactivity of stress response mechanisms or of the HPA axis anxiety and depression and abnormalities in the circadian rhythm (circadian sleep-wakefulness control). By definition, the acute form does not last longer than four months. 13 Acute insomnia results from a triggering causal factor that is easily identifiable in an individual who has not had insomnia before. Insomnia consists of three basic types: acute insomnia, primary chronic insomnia, and associated insomnia. adults 20 years of age and older reported that they had taken prescription sleep aids during the previous 30 days. 7 In the National Health and Nutrition Examination Survey (2005–2010), approximately 4% of U.S. slept seven to eight hours and that 28% slept six or fewer hours in a 24-hour period. 6 Data from the years 2008 through 2010 from the National Health Interview Survey indicated that 62% of adults in the U.S. 5 Insomnia is more common in women (25%) than in men (18%), and its prevalence increases with age, affecting approximately 50% of the elderly population. have chronic sleep and wakefulness disorders. 4Īn estimated 50 million to 70 million adults in the U.S. Insomnia is associated with one or more of the following symptoms: difficulty initiating sleep (sleep-onset insomnia or initial insomnia) difficulty maintaining sleep (sleep-maintenance insomnia or middle insomnia) and early-morning awakening with the inability to return to sleep (late insomnia). 1, 3Īccording to the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5), insomnia is defined as dissatisfaction with sleep quantity or quality that results in clinically significant distress or impairment in social, occupational, or other important areas of functioning. It synchronizes the body with the environment’s light–dark cycle, peaking during the night and dipping during the day, to stabilize the body’s natural circadian rhythm. Melatonin is a hormone that plays an integral role in diurnal rhythms. It is hypothesized that the action of orexin changes the activity of the neurotransmitters involved in the regulation of sleep/wake states. Orexin, which is produced in the hypothalamus, is a neuropeptide that plays an important role in maintaining wakefulness. These neurotransmitters contribute to maintaining wakefulness and significantly decrease during REM sleep. The sleep–wake cycle is also affected by neurotransmitters released by reticular activating system (RAS) neurons, such as norepinephrine, acetylcholine, and serotonin. Increased GABA and decreased histamine release induce NREM sleep by deactivating the cortex and thalamus. These neurotransmitters have opposing actions on the sleep–wake cycle. In the forebrain and hypothalamus, neurons release gamma-aminobutyric acid (GABA) and histamine. Sleep is regulated by a variety of chemicals in the body. 1 REM sleep correlates with activities of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system in healthy humans. Later in the cycle, when the individual enters REM sleep, electrical activity in the brain increases, contributing to increased blood flow to the brain, changes in respiratory and cardiac rates, and dreaming. NREM sleep is subdivided into three stages in which brain activity, eye movement, and skeletal muscle tone progressively decrease, placing the individual in a deeper state of sleep. Sleep typically begins with the NREM phase, which is followed by the REM phase. People experience two forms of sleep: rapid eye movement (REM) and nonrapid eye movement (NREM).
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