Medically reviewed by Smita Patel, DO, Susan Kerrigan, MD and Marianne Madsen on January 9, 2023
“Fancy a nightcap?”
We’ve all seen TV shows and movies where one of the characters asks another if they’d like a drink before going to sleep. But what are the effects of alcohol on sleep? Will a glass of wine with dinner or a hot toddy at bedtime put you to sleep or keep you awake?
Sleep Cycles
Every night of sleep comprises a sleep cycle of three non-rapid eye movement (nREM) stages and one rapid eye movement (REM) stage.
The first stage of nREM is light sleep, where all parts of the body begin to relax and wind down.
As you transition to the next sleep stage and get closer to deep sleep, your breathing and heart rate continue slowing. Your eyes also stop moving, your brain wave activity slows, and your body temperature drops. You will spend the longest time in this stage.
The final stage of nREM is when you are in the deepest stage of sleep. Your heartbeat, brain wave activity, and breathing rate are at their lowest levels during your sleep, and this is when it is the hardest to wake you. This stage is known as slow-wave sleep.
After about 90 minutes, you enter REM sleep. You begin to move back to a lighter level of sleep as your breathing, brain activity, and heart rate all begin to pick up. Your eyes also begin to move rapidly from side to side behind your eyelids. This is also the stage when you will have dreams.
Alcohol and Sleep Cycles
Alcohol is a central nervous system depressant, meaning it’s a drug that slows down brain activity. It also acts as a relaxant, which might be why people use it to unwind at the end of a long day. All this may lead you to believe that alcohol helps you to sleep better.
It is true that because alcohol is a sedative, you are likely to fall asleep quicker. However, because the sedative effects wear off after a few hours of sleep, it creates an imbalance in your first few sleep cycles. This imbalance will keep you unnaturally sedated in slow-wave sleep for longer and REM for less time, resulting in poor sleep quality and duration. According to one 2018 study, moderate drinking, meaning just two servings of alcohol per day, could reduce your sleep quality by 24%.
Alcohol and Insomnia
Poor sleep duration and quality are part of several factors that contribute to insomnia. If you are not getting enough restorative sleep, you will likely suffer daytime sleepiness the next day. To combat that, you may decide to drink caffeinated drinks and other stimulants to stay awake during the day. By the time you’re ready to go to sleep, the stimulants may still be in your system, and you can’t relax and fall asleep. So to combat the negative effects of the stimulants, you pour yourself another alcoholic drink as a sedative. Now the vicious cycle begins, further disrupting your body’s normal sleep pattern and sleep-wake cycle.
Raised Tolerance Levels
The more you drink, the more your body begins to develop a tolerance for some of the effects of alcohol. This tolerance may mean that you need to drink more to benefit from alcohol’s sedating effect. Chronic drinkers, binge drinkers, and people who suffer from alcohol abuse tend to suffer from insomnia.
Sleep Apnea
Sleep apnea is a sleep disorder where a person suffers from difficulty breathing during sleep. In some cases, they may temporarily stop breathing for a few seconds. The most common type is obstructive sleep apnea (OSA), where your upper airway becomes blocked, reducing or completely stopping any airflow. Due to the repeated lapses in breathing, sleep apnea patients typically suffer from poor sleep quality.
Alcohol consumption contributes to sleep apnea because it relaxes your throat muscles making it easier for your airway to get blocked. According to some studies, drinking alcohol could increase your chances of sleep apnea by around 25%.
There is a strong relationship between alcohol and its disruptive effects on sleep. Like caffeine, the time of day you stop drinking is a major factor of what effect it will have on your sleep. Research indicates that alcohol can remain in your system for at least six hours after drinking. Therefore, if you want to make sure you get good restful sleep, maybe it’s best to skip that infamous nightcap.
References
- Brain Basics: Understanding Sleep
- Alcohol
- The Effects of Alcohol on Quality of Sleep
- Chapter 24 – Alcohol and the sleeping brain
- Alcohol and Tolerance
- Sleep Apnea
- What is Sleep Apnea?
- Alcohol and the risk of sleep apnoea: a systematic review and meta-analysis
- Disturbed Sleep and Its Relationship to Alcohol Use
