Drinking alcohol before going to bed may help for falling asleep but it could interfere with staying asleep, researchers have found.

The Japanese study assigned 10 healthy men with an average age of about 22 to drink three different alcohol beverages over three weeks:

  • 0 grams as a control.
  • 0.5 gram as a low dose of alcohol.
  • One gram of pure ethanol per kilogram of body weight as a high dose.

The men had the drinks about 100 minutes before going to bed.

On the day of the experiment, investigators hooked up the participants to an electrocardiogram for 24 hours to record their heart rate variability.

The heart findings suggested alcohol interferes with the restorative functions of sleep, the researchers reported in the upcoming November issue of Alcoholism: Clinical & Experimental Research.

"It is generally believed that having a nightcap may aid sleep, especially sleep initiation," said Seiji Nishino, director of the Sleep and Circadian Neurobiology Laboratory at Stanford University School of Medicine in California.

"This may be true for some people who have small amounts of alcohol intake. However, it should be noted that large amounts of alcohol intake interfere with sleep quality and the restorative role of sleep and these negative consequences may be much larger during chronic alcohol intake," he added in a release.

As alcohol consumption increased, heart rate measurements increased.

Alcohol interferes with 'rest and digest'

Normally when we sleep at night, the part of the nervous system that is responsible for 'rest-and-digest' activities dominates.

But the alcohol seemed to interfere with this, which can result in insomnia, difficulty getting to sleep, early-morning awakening, lack of a sense of deep sleep and difficulty maintaining sleep, the researchers said.

"The results of this study suggest that ethanol interferes with the restorative functions of sleep," the study's authors concluded.

They suggested that doctors who treat physical and psychological disorders related to alcohol to consider the disturbing effects that habitual drinking can have on sleep.