*Nothing in this article constitutes medical advice. Seek the guidance of a physician if you have any questions.*
At first glance, the answer to this question may seem obvious: it decreases sleep quality. However much anecdotal evidence a person may have about their post-drinking sleep, the science is a fair bit more complicated. Let’s take a look at some of the underlying science about the connection between alcohol and sleep.
What Is Alcohol?
There are many different kinds of “alcohol” - it is a broad chemical classification. The kind of alcohol that is contained within alcoholic beverages is called “ethanol.” It has the chemical formula C2H5OH.
Broadly, all drinking alcohol is produced in the same manner, more or less: yeast and sugar. When deprived of oxygen, yeast will utilize the sugar to produce energy, creating ethanol as a byproduct. For low-alcohol-by-volume (ABV) beverages, such as beer or wine, this fermentation process is coupled with flavoring additions. These additions can be malt or barley (as with beer) or different types of grapes (as with wine).
For higher ABV beverages - hard alcohols - the production process also includes a “distillation” step. Yeast can only survive alcohol concentrations up to around 15%, similar to that of most wines. For spirits like gin, whiskey, or vodka, this 15% base spirit must be refined and concentrated to produce a higher ABV. Often this final number ends up being around 40-50% alcohol.
For the purposes of standardization, the United States National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines a concept known as the “standard drink,” an amount of alcoholic beverage that contains 14 grams of pure ethanol. This definition is important because the same volume of two different beverages may well contain drastically different amounts of alcohol. For example, a 12oz beer that is 5% ABV has roughly 16 grams of ethanol - equivalent to about 1.14 standard drinks. The same volume (12oz) of 80-proof (40% ABV) gin contains about 136 grams of pure ethanol - about 9 standard drinks!
The NIAAA defines the following volumes for various alcoholic beverages as one “standard drink” each:
- Beer: 12 ounces of regular beer, usually about 5% ABV
- Wine: 5 ounces of wine, typically about 12% ABV
- Spirits:5 ounces of distilled spirits, about 40% ABV
What Is the “Sleep Cycle?”
Now, to understand alcohol’s effects on sleep, we have to better understand sleep itself. Sleep doctors, somnologists, generally refer to four different stages of sleep that make up one “cycle.” A person may go through anywhere from 3-7 cycles a night, dependent on both sleep quality and length. Let’s look at each stage in turn.
Stage 1 (N1)
Stage 1, also known as N1, is a stage of non-rapid-eye-movement sleep (more on that later). This is the shortest stage, typically lasting only a few minutes. It can be easy to fall into this stage if a person “dozes off” or starts “daydreaming.” In this stage, our brains and bodies begin to slow, but they are still very receptive to outside stimuli.
Stage 2 (N2)
N2 is a significantly longer sleep stage than N1. During the first cycle, N2 usually lasts about 10-25 minutes. As each cycle passes, N2 tends to grow longer and longer. N2 is marked by a drop in body temperature, a relaxation of the muscles, and deeper sleep.
Stage 3 (N3, Slow-Wave Sleep (SWS), Delta Sleep, Deep Sleep)
One of the common names to reference stage 3 is “delta sleep.” This is due to the predictable and easily identifiable pattern of brain waves that occur - delta waves. In opposition to stage 2, stage 3 tends to start off lasting about 30 minutes, but it decreases with each progressive cycle.
Stage 4 (REM)
Stage 4 is the first stage of sleep that involves “rapid eye movement.” As the name suggests, REM sleep is characterized by a frequent and often intense fluttering of the eyes (even though they are closed). This stage of sleep is particularly interesting because brain activity rises to levels seen during waking hours. There is a significant body of evidence to support the conclusion that REM sleep is essential for cognitive functions like memory and creativity.
Alcohol’s Effects on the Sleep Cycle
Alcohol and sleep have a complicated relationship. Anyone who has had a few too many to drink knows first hand that, although it can be easy to fall asleep quickly, this sleep is if not of high quality. Our understanding of ethanol and the sleep cycle and help us understand the connection.
Ethanol is a sedative. In common terms, it is sometimes referred to as a “downer.” This means that it suppresses the central nervous system. In effect, this causes individuals who have consumed alcohol to fall asleep faster than normal. While this may sound great, this causes an imbalance between N3 and REM sleep, generally decreasing the length of REM sleep during the first two cycles. This imbalance decreases overall sleep quality.
Insomnia is one of the most commonly reported sleep disorders amongst people do drink alcohol. According to the Mayo Clinic, insomnia is “a common sleep disorder that can make it hard to fall asleep, hard to stay asleep, or cause you to wake up too early and not be able to get back to sleep.” In effect, people with insomnia have a hard time getting good, quality sleep.
Alcohol-triggered insomnia can present in a very bad cycle. Individuals who already drink experience a decrease in sleep quality, making them tired during the day. Those individuals use caffeine or other stimulants to stay awake, which makes it harder to fall asleep at night. Then, they consume alcohol to help them fall asleep at night. This cycle can have horrible effects on memory, cognition, and mood.
Sleep apnea is a disease characterized by temporary, short lapses in breathing during sleep. These lapses are powerful enough to wake a patient, thus disrupting their sleep cycle. Although there lifestyle factors that overlap with drinking that can cause sleep apnea (such as obesity) several studies have indicated that heavy drinking increases an individual’s risk of developing sleep apnea by 25%.
If any of these conditions sound familiar to you or a loved one, contact your physician.