Alcohol and Sleep
Many of us have indulged in a glass of wine to help send us off to bed, and more than 1 in 10 people (1) uses alcohol to beat stress-related insomnia and sleep better at night. However, the bulk of the evidence shows that alcohol doesn't improve sleep (2). On the contrary, as alcohol passes through the body, it exerts a number of biochemical effects that tend to lead to poorer sleep. Understanding the effects of alcohol on sleep is the first step toward preventing alcohol-related sleep problems.
Although consuming alcohol before bedtime helps you fall asleep faster, the popular beverage negatively affects overall sleep quality (3). When you consume alcohol before bed, your body metabolizes the alcohol throughout the night. As blood alcohol levels rise and fall, alcohol exerts different effects on your sleep.
How Does Alcohol Affect Sleep?
Alcohol potentially causes a shorter overall sleep time (4) and disrupted sleep, which lead to next-day fatigue and sleepiness. The more alcohol you drink (5), the greater the negative effects on your sleep.
Alcohol Alters Sleep Stages
For most people, alcohol induces a deeper-than-usual sleep in the first half of the night, followed by disrupted sleep in the second half of the night.
During a normal night of sleep (6), we cycle through periods of light sleep, deep sleep, and rapid eye movement (REM) sleep. Each sleep stage plays an essential function, but deep sleep and REM sleep are considered the most important stages for physical and mental restoration.
Alcohol initially acts as a sedative, increasing the proportion of deep sleep at the beginning of the night. However, as the alcohol's effects start to wear off, the body spends more time in light sleep, which is not as sound and may lead to more nighttime awakenings. As a result of these frequent awakenings, people tend to clock fewer hours sleeping (7) after drinking alcohol.
Studies have found conflicting information about how alcohol affects REM sleep. Alcohol appears to consistently delay the first REM sleep episode, and higher doses of alcohol appear to reduce the total amount of REM sleep. Suppressing REM sleep can have detrimental consequences for memory consolidation (8) and other cognitive processes.
People who consistently drink too much alcohol may eventually build up a tolerance to its initial sedative effects. Studies of chronic alcohol users have found that these individuals typically experience disrupted sleep patterns with less slow wave sleep and more REM sleep.
Alcohol Affects Levels of Adenosine and Sleep Homeostasis
Alcohol increases levels of adenosine, a key component of the homeostatic drive. The homeostatic drive is responsible for keeping our body balanced, and it's one of the major mechanisms that regulates the sleep-wake cycle. The homeostatic drive prompts sleep by boosting levels of adenosine when we've been awake for too long.
After a few drinks, these increased adenosine levels send us into a deep sleep. However, once the body realizes it's had too much slow wave sleep, the homeostatic drive compensates by allowing us less deep sleep in the second half of the night.
In the short term, these alterations to our sleep pattern can lead to a restless second half of the night. In the long term, frequent disruptions to our natural sleep cycle may alter the homeostatic drive in a more permanent way. People who abuse alcohol long-term don't seem to display the deep recovery sleep that most people show after sleep deprivation, suggesting that the homeostatic drive is no longer functioning as it should.
Alcohol Alters Melatonin and the Circadian Rhythm
Alcohol may also exert some of its effects on sleep by influencing the circadian rhythm. The circadian rhythm is responsible for keeping the body anchored to a 24-hour cycle. As part of this 24-hour cycle, the body releases a hormone called melatonin to prepare us for sleep in the evening. Older studies have found that drinking alcohol before bedtime lowers melatonin levels (9) and interferes with core body temperatures, which in turn impacts sleep quality.
A newer study found that one dose of alcohol (10) had no effect on the circadian rhythm in rodents. However, the researchers proposed that perhaps these effects on the circadian rhythm are only seen after several consecutive days of alcohol consumption. In support of the alcohol-melatonin connection, researchers have noticed that individuals suffering from severe alcohol withdrawal tend to have less pronounced melatonin levels and release.
Alcohol Increases Snoring and Symptoms of Obstructive Sleep Apnea
Substantial evidence suggests that alcohol worsens symptoms of snoring and obstructive sleep apnea. These sleep-related breathing difficulties occur when soft tissues collapse and block the upper airway (11). In mild cases, breathing difficulties lead to snoring sounds. In more serious cases, individuals suffer momentary lapses in breathing, followed by micro-awakenings that interrupt the progression of the sleep stages.
Alcohol is a muscle relaxant (12), so consuming alcohol at bedtime can make a person more prone to experience a blocked airway. People who typically snore or who have obstructive sleep apnea tend to display more severe snoring and lower blood oxygen levels (13) after drinking alcohol, especially when they drink close to bedtime. People who regularly drink alcohol are 25% more likely to have obstructive sleep apnea, although the connection may be partly due to other shared risk factors such as obesity.
Alcohol Exacerbates Existing Health Conditions and Sleep Disorders
Many people turn to alcohol to cope with difficult feelings, but alcohol may end up having the opposite effect if it interferes with sleep. For example, people with moderate or severe anxiety who use alcohol in hopes of sleeping better are actually more likely to have sleep problems (14). Similarly, studies on bereaved individuals (15) have found that using alcohol to cope with grief increases the risk of developing major depression, which is itself a risk factor for sleep disturbances (16).
Unsurprisingly, studies of people with insomnia have also found that heavy alcohol use exacerbates insomnia (17). People who wake up feeling unrefreshed may be more likely to rely on alcohol again to help them sleep the next night, leading to a counterproductive pattern of alcohol use.
Can You Drink Within Certain Limits?
Proceed with caution when drinking before bedtime, as alcohol may be affecting your sleep more than you realize. This may be especially true if you drink alcohol to help you fall asleep faster, and then experience disrupted sleep later in the night without realizing it. Since even small amounts of alcohol (18) can affect your sleep, the overwhelming consensus in the medical community is that alcohol is not an appropriate sleep aid (19).
Since alcohol affects everyone differently (20), it's important to understand where your limit lies and how much alcohol you can drink before it starts to affect your sleep. If you're looking for ways to improve your sleep, an easy place to start is by adopting healthy sleep hygiene habits such as keeping a consistent sleep schedule and creating a calming bedroom environment.
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