Nightcap May Not Help All Night Long

Alcohol leads to faster and deeper sleep but an overall more disrupted sleep

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) There is no doubt that drinking a lot of alcohol can make a person sleepy or pass out. But alcohol can affect how a person sleeps in more complex ways as well.

A recent study analyzed all the research related to alcohol and sleep. The researchers found that alcohol can change the natural cycles that people experience during sleep.

Drinking alcohol can lead a person to fall asleep faster and increase how much time they spend in deep sleep. Alcohol also decreases the time people spend in "rapid eye movement" (REM) sleep.

While alcohol may help people fall asleep faster initially, it can cause disruptions later on in a person's sleep.

"If you drink, do so in moderation."

The study, led by Irshaad O. Ebrahim, a neuropsychiatrist at the London Sleep Centre in the United Kingdom, included a review of all the studies related to the effects of alcohol on sleep.

The researchers wanted to understand how alcohol affects the natural cycles that occur during sleep. They found 153 studies that involved alcohol's impact on sleep, but only 20 met their final criteria.

Other studies were excluded for various reasons, such as involving people with sleeping disorders, lacking sufficient data, not including an experiment or other concerns about the studies' methods.

These 20 studies included results on 38 sleep lab experiments involving a total of 517 people across all the studies.

For the purposes of the study, the researchers defined a "low dose" of alcohol as being between 0.15 and 0.49 mg/kg, which translates to about 1 to 2 standard drinks.

A moderate dose refers to 0.5 to 0.74 mg/kg, or between 2 and 4 standard drinks. A high dose of alcohol refers to anything over 0.75 mg/kg, which is approximately more than 4 standard drinks.

One of the researchers' primary findings was that people may have fallen asleep faster and deeper with alcohol, but that didn't mean they slept better all night long.

"The higher the dose, the greater the impact on increasing deep sleep. This effect on the first half of sleep may be partly the reason some people with insomnia use alcohol as a sleep aid," said Dr. Ebrahim in a release about the study. "However, the effect of consolidating sleep in the first half of the night is offset by having more disrupted sleep in the second half of the night."

Most of the time, when individuals first fall asleep, they are in NREM (non-rapid eye movement) sleep. Then they enter REM sleep. They then continue to alternate between NREM and REM sleep in approximately 90 minute cycles throughout the night.

Researchers do not fully understand all the different functions during REM and NREM, but they have learned that both are important to the rest the body needs and the processing that goes on in the brain during sleep. They have theories about both with evidence from studies.

It appears that REM sleep is the time when the brain reorganizes, processes and stores information. This stage is also the one where people dream.

NREM is a deeper stage of sleep when researchers believe the body is being restored. The two later stages of NREM sleep comprise "slow-wave sleep," or SWS. During SWS, the body works on building muscles and bone, strengthening the immune system and regenerating body tissue.

It may sound like more time spent in SWS or NREM is a good thing, but Dr. Ebrahim noted that's not necessarily the case.

"SWS or deep sleep generally promotes rest and restoration," said Ebrahim in the release. "However, when alcohol increases SWS, this may also increase vulnerability to certain sleep problems such as sleepwalking or sleep apnea in those who are predisposed."

Sleep apnea is a sleeping disorder in which a person stops breathing for at least 10 seconds at a time during the night. It is linked to various other health problems, such as obesity, diabetes and heart problems.

In general, people who drink low and moderate amounts of alcohol will not necessarily experience any clear effects from the alcohol on their REM during the first half of their sleep.

At higher doses of alcohol, however, a person's time in REM tends to be shortened during the first half of sleep. Individuals who drink moderate or high amounts of alcohol will also have an overall shorter period of time spent in REM during sleep than those with low or no alcohol.

Dr. Chris Idzikowski, the director of the Edinburgh Sleep Center, which was unrelated to this study, also spoke in the release about the implications of the study.

"In sum, alcohol on the whole is not useful for improving a whole night's sleep," Dr. Idzikowski said. "Sleep may be deeper to start with, but then becomes disrupted. Additionally, that deeper sleep will probably promote snoring and poorer breathing. So, one shouldn't expect better sleep with alcohol."

The study was published January 22 in the journal Alcoholism: Clinical and Experimental Research. Information was unavailable regarding study funding or disclosures.

Reviewed by: 
Review Date: 
January 22, 2013
Last Updated:
January 22, 2013