The study of alcohol's effects on sleep dates back to the late 1930s. Since then, an extensive literature has described alcohol's effects on the sleep of healthy, nonalcoholic people. For example, studies found that in nonalcoholics who occasionally use alcohol, both high and low doses of alcohol initially improve sleep, although high alcohol doses can result in sleep disturbances during the second half of the nocturnal sleep period. Furthermore, people can rapidly develop tolerance to the sedative effects of alcohol. Researchers have investigated the interactive effects of alcohol with other determinants of daytime sleepiness. Such studies indicate that alcohol interacts with sleep deprivation and sleep restriction to exacerbate daytime sleepiness and alcohol-induced performance impairments. Alcohol's effects on other physiological functions during sleep have yet to be documented thoroughly and unequivocally.
KEY WORDS: sleep disorder; physiological AODE (effects of alcohol or other drug use, abuse, and dependence); REM (rapid eye movement) sleep; NREM (nonrapid eye movement) sleep; circadian rhythm; melatonin; prolactin; body temperature; attention; time of day; insomnia; dose-response relationship
Alcohol affects sleep, daytime alertness, and certain physiological processes that occur during sleep. Its impact on human sleep has received much scientific study daring back to early experiments by Kleitman (1939), described in his book Sleep and Wakefulness. In that monograph, the author summarizes the effects that alcohol consumed 60 minutes before bedtime has on body temperature and motility during sleep in healthy nonalcoholic people. In the 1960s and 1970s, after scientists had identified various sleep stares (e.g., rapid eye movement [REM] sleep) and had standardized electrophysiological methods to document sleep, research on alcohol's effects on the sleep of healthy nonalcoholic and noninsomniac volunteers and on the sleep of alcoholics increased substantially. More recently, with the emergence of the field of sleep-disorders medicine, researchers and clinicians have focused their attention on alcohol's effect on primary sleep disorders, such as sleep apneas, which are short (i.e., 10 to 30 seconds l ong) episodes of breathing obstruction. This attention to sleep disorders also has sensitized investigators and clinicians to the impact that disrupted and shortened sleep has on daytime alertness. As a result, various studies have investigated the potential interactive effects of alcohol with daytime alertness and daytime functioning in both healthy people and patients with sleep disorders.
This article provides an overview of alcohol's effects on normal sleep, sleep physiology, and daytime alertness in nonalcoholic people. (The accompanying article by Brower, pp. 110-125 in this issue, discusses alcohol's effects on sleep in alcoholics.) The current article reviews normal sleep physiology describes alcohol's effects on the various sleep states and sleep stages, and explores some of the mechanisms through which alcohol may exert those effects. It then summarizes the relationship of nocturnal sleep to daytime alertness and how alcohol affects this relationship. The article ends with a discussion of alcohol's effects on sleep in people with primary insomnia.
NORMAL SLEEP PHYSIOLOGY
As most people know from their own experience, sleep is not uniform throughout the night. For example, at certain times during the night, it is very difficult to wake a sleeping person, whereas at other times, the slightest sound will alert the sleeper. Extensive studies have identified two different sleep states: REM sleep and nonrapid eye movement (NREM) sleep. Furthermore, NREM sleep can be divided into four stages based on how easy it is to arouse a sleeper (i.e., how "deep" the sleep is).
These different sleep states and sleep stages are defined based on scoring criteria for three electrophysiological measurements that were first published in 1968 and have been employed ever since in sleep laboratories around the world. …