Alcohol and sleep have a complicated relationship. A single glass of red wine is enough make some people drowsy, and too much booze of any kind will knock out even the heaviest of tipplers. But even though alcohol may initially make you sleepy, it can wreak serious havoc on your quality of sleep later in the night.
How exactly are those happy-hour beers affecting your sleep cycle? Here’s the truth about the relationship between alcohol and sleep.
The connection between alcohol and sleep
In general, alcohol quickens how fast you’ll fall asleep, explains Timothy Roehrs, PhD, director of research at the Sleep Disorders and Research Center of Henry Ford Health System and professor at the School of Medicine at Wayne State University in Detroit. In addition, Roehrs says, “drinking increases the depth of sleep, meaning your arousal threshold is elevated.” (In layman’s terms: It will take more noise and commotion to wake you up than it usually does.)
What does research have to say about alcohol and sleep? Studies that have looked at brain activity in sleepers after they’ve been drinking suggest that alcohol increases the time people spend in slow wave sleep, the deepest stage of sleep—although recent data from Roehrs and his colleagues suggests that this only happens to people who are already deficient in deep sleep. (That could be you if you have a sleep disorder, such as sleep apnea.)
These effects apply only to the first part of sleep, says Roehrs. “Typically, this will all occur within the first four hours of the night, as your body is metabolizing [breaking down] the alcohol in your body.” Once you’ve metabolized all the alcohol, it will have a paradoxical effect on sleep. “Now you’re awakened, and you arouse from sleep more easily,” Roehrs says.
Not surprisingly, studies on alcohol and sleep show that in the later part of the night, after you’ve downed a few cocktails, you tend to spend more time in the lighter stages of sleep and REM sleep (the period when you dream).
Is one drink enough to ruin a whole night’s sleep?
When it comes to how alcohol will affect any one individual, a lot of factors come into play, including how much you drink, when you drink, what you drink, and what you weigh. Research that Roehrs and his colleagues conducted for the National Institute on Alcohol Abuse and Alcoholism shows that the amount of alcohol that will interfere with sleep is whatever amount raises your blood alcohol concentration (BAC) to 0.04. BAC is a measure of how much alcohol is in your system. (Remember: A BAC of 0.08 is the point at which you’re legally considered intoxicated and can’t drive in all 50 states in the U.S.)
For most people, it would take drinking about one or two drinks in an hour to reach a BAC of 0.04, but that also depends on your body weight, gender, what you’ve eaten (carbs absorb some of the alcohol, slowing the rate at which your BAC rises), and other factors. Drink size matters, too. We’re referring to standard-size pours here: a 12-ounce beer, five-ounce glass of wine, or 1.5 ounces of distilled 80-proof liquor.
Alcohol can make existing sleep problems worse
If you already have a sleep problem, such as insomnia, sleep apnea, or a parasomnia (such as sleepwalking or sleep talking), drinking can actually heighten those disorders and make getting a good night’s sleep even more difficult.
Many people with insomnia claim that drinking alcohol before bed helps them sleep. It’s not so clear-cut, though. Research from Roehrs and his colleagues shows that just as alcohol can increase the amount of deep sleep in healthy individuals who are deep-sleep-deprived, drinking can also increase the amount of deep sleep that people with insomnia get. But after about six nights, those individuals start to develop a tolerance to the alcohol—and they need to drink more to get the same effect. While the existing evidence isn’t yet conclusive, Roehrs adds, it suggests that using alcohol as a sleep aid for people with insomnia could increase the risk of alcohol abuse.
Because alcohol depresses the central nervous system, it slows down the part of your brain that controls breathing, too—along with the firing of the muscles that keep your airway open, says Roehrs. For people with sleep apnea, this part of the airway gets repeatedly blocked during sleep, causing brief arousals throughout the night. So for those with sleep apnea and those who are at risk of developing sleep apnea, research shows drinking can exacerbate the problem.
If you’re someone who suffers from a parasomnia, such as sleepwalking or sleep talking, drinking can also make these problems worse, notes Roehrs. People with parasomnias (sleep disorders caused by arousals during different stages of sleep) typically experience these episodes in stage three or four of sleep. And because drinking alcohol can increase the amount of time an individual will spend in these deep stages of sleep, it can make experiencing a parasomnia episode more likely.
How to sleep better when you do drink
The bottom line: Drinking alcohol isn’t going to do your sleep any favors—but if you’re smart about when, what, and how much you imbibe, a glass (or two) of Pinot noir won’t necessarily ruin your night, either. Here are a few tips to keep in mind.
1. Stop drinking a few hours before bed.
Exactly how long you should leave between your last drink and hitting the pillow depends on how much you drink and how quickly your body metabolizes alcohol. Most of us metabolize about one drink every one to two hours, says Roehrs.
2. Don’t overdo it.
The more drinks you consume, the longer it takes the body to metabolize the alcohol. Regardless of whether your body metabolizes alcohol quickly or on the slower end of the spectrum, the less alcohol in your system, the less potential for your sleep to get disrupted.
3. Watch out for heavy pours.
Stick to standard-size drinks, not doubles, extra-large wine glasses, or mixed drinks with multiple shots of different liquors. Bonus: You’ll certainly save money the next time you hit the bar. We’ll raise a glass to that.