Alcohol and Sleep
Alcohol Alert From NIAAA
The average adult sleeps 7.5 to 8 hours every night. Although the function of sleep is unknown, abundant evidence demonstrates that lack of sleep can have serious consequences, including increased risk of depressive disorders, impaired breathing, and heart disease. In addition, excessive daytime sleepiness resulting from sleep disturbance is associated with memory deficits, impaired social and occupational function, and car crashes (1,2).
Alcohol consumption can induce sleep disorders by disrupting the sequence and duration of sleep states and by altering total sleep time as well as the time required to fall asleep (i.e., sleep latency).
This Alcohol Alert explores the effects of alcohol consumption on sleep patterns, the potential health consequences of alcohol consumption combined with disturbed sleep, and the risk for relapse in those with alcoholism who fail to recover normal sleep patterns.
Sleep Structure, Onset, and Arousal
Before discussing alcohol's effects on sleep, it is helpful to summarize some basic features of normal sleep. A person goes through two alternating states of sleep, characterized in part by different types of brain electrical activity (i.e., brain waves). These states are called slow wave sleep (SWS), because in this type of sleep the brain waves are very slow, and rapid eye movement (REM) sleep, in which the eyes undergo rapid movements although the person remains asleep.
Most sleep is the deep, restful SWS. REM sleep occurs periodically, occupying about 25 percent of sleep time in the young adult. Episodes of REM normally recur about every 90 minutes and last 5 to 30 minutes. REM sleep is less restful than SWS and is usually associated with dreaming. Although its function is unknown, REM appears to be essential to health. In rats, deprivation of REM sleep can lead to death within a few weeks (3). In addition, a transitional stage of light sleep occurs at intervals throughout the sleep period (4).
Sleep was formerly attributed to decreased activity of brain systems that maintain wakefulness. More recent data indicate that sleep, like consciousness, is an active process. Sleep is controlled largely by nerve centers in the lower brain stem, where the base of the brain joins the spinal cord. Some of these nerve cells produce serotonin, a chemical messenger associated with sleep onset (5) and with the regulation of SWS. Certain other nerve cells produce norepinephrine, which helps regulate REM sleep and facilitates arousal (6). The exact roles and interactions of these and other chemical messengers in orchestrating sleep patterns are not known (6). Significantly, however, alcohol consumption affects the function of these and other chemical messengers that appear to influence sleep.
Alcohol and Sleep in Those Without Alcoholism
Alcohol consumed at bedtime, after an initial stimulating effect, may decrease the time required to fall asleep. Because of alcohol's sedating effect, many people with insomnia consume alcohol to promote sleep. However, alcohol consumed within an hour of bedtime appears to disrupt the second half of the sleep period (7). The subject may sleep fitfully during the second half of sleep, awakening from dreams and returning to sleep with difficulty. With continued consumption just before bedtime, alcohol's sleep-inducing effect may decrease, while its disruptive effects continue or increase (8). This sleep disruption may lead to daytime fatigue and sleepiness. The elderly are at particular risk, because they achieve higher levels of alcohol in the blood and brain than do younger persons after consuming an equivalent dose. Bedtime alcohol consumption among older persons may lead to unsteadiness if walking is attempted during the night, with increased risk of falls and injuries (3).
Alcoholic beverages are often consumed in the late afternoon (e.g., at "happy hour" or with dinner) without further consumption before bedtime. Studies show that a moderate dose1 of alcohol consumed as much as 6 hours before bedtime can increase wakefulness during the second half of sleep. By the time this effect occurs, the dose of alcohol consumed earlier has already been eliminated from the body, suggesting a relatively long-lasting change in the body's mechanisms of sleep regulation (7,8).
The adverse effects of sleep deprivation are increased following alcohol consumption. Subjects administered low doses of alcohol following a night of reduced sleep perform poorly in a driving simulator, even with no alcohol left in the body (9,10). Reduced alertness may potentially increase alcohol's sedating effect in situations such as rotating sleep-wake schedules (e.g., shift work) and rapid travel across multiple time zones (i.e., jet lag) (9). A person may not recognize the extent of sleep disturbance that occurs under these circumstances, increasing the danger that sleepiness and alcohol consumption will co-occur.
