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I don’t drink a lot. It’s not because I don’t appreciate a glass of wine with a great meal, or a few beers on a hot summer evening. It’s because I know what alcohol can do to sleep and healthy circadian rhythms.
Alcohol is the most common sleep aid—at least 20 percent of American adults rely on it for help falling asleep. But the truth is, drinking regularly—even moderate drinking—is much more likely to interfere with your sleep than to assist it.
Does this mean you need to abstain from drinking altogether? Nope. But part of a smart, sleep-friendly lifestyle is managing alcohol consumption so it doesn’t disrupt your sleep and circadian rhythms.
How alcohol affects circadian rhythms—and why it matters to your health
First, a quick refresher on the importance of the body’s circadian rhythms. These 24-hour rhythms are governed by a master biological clock, a tiny region of the brain with a big job: to coordinate circadian rhythm activity throughout the body.
Circadian rhythms regulate nearly all of the body’s processes, from metabolism and immunity to energy, sleep, and sexual drive, cognitive functions, and mood.
In the body, alcohol disrupts circadian functioning, directly interfering with the ability of the master biological clock to synchronize itself. Because circadian rhythms have such a powerful, dominating influence over the way our bodies function, the disruptive effects of alcohol can be widespread, affecting sleep and other systems, including:
Poor liver function. The liver acts as a filtering system for the body, helping metabolize food and chemicals (including alcohol itself), and pulling toxins from the bloodstream. Like nearly all of the body’s organs, the liver functions according to circadian rhythms. Alcohol interferes with these circadian rhythms regulating the liver, and can contribute to compromised liver function, liver toxicity, and disease.
Leaky gut. The gut and its microbiome are often referred to as the body’s second brain, and operate under powerful circadian rhythm activity. The circadian disruption that can result from alcohol consumption contributes to leaky gut syndrome, according to research. Circadian rhythms thrown out of sync can weaken the lining of the gastrointestinal tract, making it more vulnerable to permeation—that’s the leakiness that allows bacteria, toxins, and food to leave the intestines and enter the bloodstream.
Depression. There’s a complicated relationship among depression, alcohol, and sleep. People suffering from depression may already have disrupted circadian rhythms, and the presence of even moderate amounts of alcohol may push those rhythms further out of sync.
Disrupted sleep-wake cycles. Alcohol is highly effective at suppressing melatonin, a key facilitator of sleep and regulator of sleep-wake cycles. Research indicates that a moderate dose of alcohol up to an hour before bedtime can reduce melatonin production by nearly 20 percent. Alcohol has a direct effect on circadian rhythms, diminishing the ability of the master biological clock to respond to the light cues that keep it in sync. Those effects of alcohol on the biological clock appear to persist even without additional drinking, according to research.
There’s also evidence alcohol interferes with the body’s other sleep-wake regulator: its internal sleep drive. Alcohol elevates levels of adenosine, a chemical that regulates sleep by rising naturally in the body the longer you’ve been awake, and increasingly blocking other chemicals that stimulate wakefulness. Alcohol’s adenosine-boosting effects make you sleep at times other than you would be naturally, and can throw your natural sleep-wake cycle off course.
Circadian rhythms affect how the body responds to alcohol, depending on the timing of alcohol intake. Long-established research shows the body metabolizes alcohol differently at different times of day. Studies have shown the body is more effective at processing alcohol at certain times of the day than others.
The most effective time of day for the body to metabolize alcohol, according to research? Early to middle evening hours. That’s right, the traditional “happy hour” time is actually when the body is most prepared to process that cocktail. The time of day when the body is least well prepared? Morning. If that mimosa with brunch hits you particularly hard, it may be the result of circadian timing.
How alcohol affects sleep
Before we look at the effects of alcohol on sleep in detail, here’s the basic bottom line. The more you drink, and the closer your drinking is to bedtime, the more it will negatively impact your sleep. Even moderate amounts of alcohol in your system at bedtime alters sleep architecture—the natural flow of sleep through different stages. It also leads to lighter, more restless sleep as the night wears on, diminished sleep quality, and next-day fatigue.
What does drinking alcohol do to a night of sleep?
It’s true, sleep may happen more quickly after consuming a drink or two. Alcohol often does reduce sleep onset latency—the time it takes to fall asleep. Depending on how much alcohol is consumed, however, what seems like falling asleep may be something closer to passing out. And we quickly build a tolerance for the sedative effects of alcohol, which means you may need to drink more to have the same initial sleep-inducing effects.
For many people who drink moderately, falling asleep more quickly may seem like an advantage of a nightly glass of wine. But alcohol goes on to affect the entire night of sleep to come.
In the first half of the night, when the body is metabolizing alcohol, studies show people spend more time in deep, slow-wave sleep and less time in REM sleep. It may sound like a good idea to spend more time in deep sleep. Not so fast. Sleep architecture is biologically driven and finely calibrated to meet the body’s needs during nightly rest—changes to the natural, typical structure of sleep aren’t generally good for health or well being. REM sleep, which gets shortchanged in the first half of the night under the influence of alcohol, is important for mental restoration, including memory and emotional processing.
During the second half of the night, sleep becomes more actively disrupted. As alcohol is metabolized and any of its sedative effects dissipate, the body undergoes what scientists call a “rebound effect.” This includes a move from deeper to lighter sleep, with more frequent awakenings during the second half of the night. (These may be micro-awakenings that the sleeper doesn’t even remember—but they still interrupt the flow, and quality, of sleep.) During the second half of the night, sleep architecture shifts again away from normal, with less time spent in slow wave sleep. The rebound effect may include more time in REM—a lighter sleep stage from which it is easy to be awakened.
People who go to bed with alcohol in their system may be more likely to wake early in the morning and not be able to fall back to sleep, another consequence of the rebound effect.
Other sleep disruptions associated with alcohol consumption include:
More frequent need to get up and go to the bathroom, especially during the second half of the night
- Increased risk for parasomnias including sleepwalking and sleep eating
- Greater risk for snoring and sleep-disordered breathing. Alcohol can lead to excessive relaxation of the muscles in the head, neck, and throat, which may interfere with normal breathing during sleep.
- Alcohol consumption can trigger new sleep disorders or exacerbate existing ones, including insomnia and obstructive sleep apnea
Sleep and circadian rhythm disruption from alcohol also contribute to next-day tiredness, fatigue, irritability, and difficulty concentrating. Even if it doesn’t present as a full-fledged hangover, alcohol-related sleep loss negatively affects mood and performance.
There’s also a gender factor in the effects of alcohol on sleep: Women appear to experience the sleep-disrupting impact of alcohol more significantly than men do, according to research.
How much alcohol is too much for sleep?
Heavy drinking can make the sleep- and circadian rhythm-disrupting effects of alcohol worse. But even a regular, moderate routine of two to three drinks a day is enough to create sleep and performance problems for many people.
I recommend to my patients drinking two to three times a week. That recommendation is the same for both men and women. This provides enough room to enjoy an after-work cocktail with friends, indulge in a glass of wine at your favorite restaurant, and crack open a beer after a weekend’s worth of chores around the house—all without interfering with healthy sleep and circadian rhythms.
Does this routine mean opting for something different at times when you might otherwise have alcohol? For many people, the answer is yes. But as so many of my patients tell me, it’s worth it: for the improvements to the quality of their sleep, their increased energy during the day, and the boost many of them experience in mental sharpness and clarity. Cheers to that.
