How alcohol affects your brain during sleep

If you want to get a restful night’s sleep, an alcoholic nightcap isn’t the best way to go. In a new journal article in Alcoholism: Clinical and Experimental Research, scientists reviewed all known studies of how boozing affects snoozing in healthy individuals.

Led by Dr. Irshaad Ebrahim, medical director of the London Sleep Centre, the authors found that drinking alcohol can have a big impact on your sleeping brain. And that, in turn, can affect how refreshed and alert you feel the following day.

Here’s a glance at what happens inside your brain when you doze off with alcohol in your system.

At Bedtime

Alcohol is a sedative, so it makes falling asleep easier. Dr. Ebrahim and his colleagues found that this holds true whether people drink a little or a lot.

First Half of the Night: Deep Sleep

Slow-wave sleep—deep sleep associated with slow brain waves—is crucial for overall health. The body repairs and regenerates tissue, builds bone and muscle, and may strengthen the immune system during this sleep stage. Slow-wave sleep is also necessary for feeling rested and energetic the next day.

Dr. Ebrahim and his team found that alcohol increases slow-wave sleep during the first half of the night. That might sound like a good thing. However, according to Dr. Ebrahim, deeper sleep may worsen sleep apnea and sleepwalking in vulnerable individuals. Plus, any gains made during the first half of the night may be offset by fitful sleep later.

First Half of the Night: REM Sleep

Rapid eye movement (REM) sleep—named for the way the eyes dart around rapidly behind closed lids—is the type of sleep in which dreaming typically occurs. REM sleep stimulates regions of the brain used to learn and form memories. Scientists believe that the brain may use this time to sort and selectively store new information acquired during waking hours.

Normally, periods of REM sleep alternate with non-REM sleep, starting about 90 minutes after dozing off and continuing throughout the night. Studies show that heavy drinking (more than four drinks) decreases REM sleep in the first half of the night. According to Dr. Ebrahim, lack of enough REM sleep may have a negative effect on concentration, motor skills, and memory during the day.

Second Half of the Night

As the night goes on, sleeping under the influence causes more problems. The quality of sleep is disrupted, and people often wake up in the middle of the night as the effects of alcohol wear off. Having two to four (or more) drinks before bedtime also reduces the total amount of REM sleep.

The Next Day

People who drink close to bedtime may wake up tired and cranky—and not only those who stayed out until 3 a.m. Especially if you had more than one or two drinks, you may have symptoms of sleep deprivation the next day, including drowsiness, moodiness, and trouble focusing. You may take longer to finish tasks, make more errors at work or school, and be more prone to careless accidents.