Those who have had a rough night out drinking may know the booze can deepen nighttime sleep only to wake you up as the sun is rising. Turns out this so-called rebound effect strikes women more than men, according to a new study in which a group of 20-somethings got drunk in the name of science. 

Alcohol's sleepy effects have not gone unnoticed.

"It's clear that a substantial portion of the population uses alcohol on a regular basis to help with sleep problems," lead researcher J. Todd Arnedt, assistant professor of psychiatry and neurology at the University of Michigan, said in a statement. "This perception may relate to the fact that alcohol helps people fall asleep quickly and they may be less aware of the disruptive effects of alcohol on sleep later in the night."

Until now, Arnedt said, very few alcohol-administration studies have included women, and since females metabolize alcohol differently than men, there could be gender differences in its effects on sleep. In addition, women seem to be downing alcohol more today than years ago. A study reported in the July 2009 issue of the Journal of the American Academy of Child and Adolescent Psychiatry showed a 30 percent jump between 1979 and 2006 in women who binge drink (that is, who down at least four alcoholic drinks in rapid succession).

Arnedt noted that the current study was based on a secondary analysis of data and so they should be considered preliminary results that must be confirmed with further research.

Intoxicating study

To get the scoop on how women's sleep fared after imbibing, the researchers recruited 93 healthy adults, 59 women and 34 men, with an average age of 24, and 29 of whom had a family history of alcoholism.

"Our decision to examine family history was based on some observational studies showing different sleep characteristics among family-history positive participants compared to family-history negative participants," Arnedt explained. "Family-history positive individuals also seem to be more resistant to the acute intoxicating effects of alcohol than individuals without a family history of alcoholism."

Participants were told they would receive a placebo on one night and alcohol on the other. Between 8:30 p.m. and 10 p.m. participants drank either a nonalcoholic placebo beverage or an alcoholic one (bourbon or vodka) to the point of intoxication (for the alcohol drinkers). Breath tests determined intoxication.

The alcoholic drinks were a mix of 1 part alcohol to 4 parts caffeine-free soda, while the placebo was the equivalent amount of soda with a few drops of vodka or bourbon floated on top. But this was not a raucous party: "We tried to do it in as controlled a way as we could so try to reduce the appearance of it being a party atmosphere and [maintained the] scientific integrity of it," Arnedt told LiveScience.

The volunteers had eight hours to sleep between 11 p.m. and 7 a.m., while electrodes recorded electroencephalograms (EEG), electromyograms (EMG, or electrical activity of muscles and nerves) and electrocardiograms (EKG). A trained sleep technician also noted limb movements, respiration factors and other sleep variables.

Once awakened at 7 a.m., they completed questionnaires about how often they drank alcohol, how sleepy they felt and their sleep quality, which included ratings about alertness, sleep refreshment  and ability to concentrate.

Most subjects indicated they knew whether they had drunk alcohol or not.

How'd you sleep?

Participants who had imbibed the prior night had worse sleep-quality ratings than the placebo group, though there was no difference in sleep-quality ratings between individuals with and without alcoholism in their families. Those who drank alcohol also spent less time in rapid eye movement, or REM, sleep compared with sober individuals. (Dreams usually occur during the REM stage of sleep, which is thought to serve various functions, including to rest a part of the brain (since some areas are active while others aren't) and to replenish brain chemicals, such as neurotransmitters.

"Alcohol increased self-reported sleepiness and disrupted sleep quality more in women than men," Arnedt said.

For instance, women who were intoxicated spent an average of 30 minutes awake after falling asleep compared with sober women's 19 minutes awake. Men didn't show such a gap, with the alcohol group of men spending about 27 minutes awake after bedtime, and sober men nearly 32 minutes.

They also found evidence to confirm alcohol's schizophrenic effects on sleep. During the first half of the night, men and women who drank alcohol slept longer with fewer awakenings and less time spent awake compared with sober participants. The reverse was found for the second half of the night with alcohol infringing on a good night's sleep.

"These differences may be related to differences in alcohol metabolism," Arnedt said, adding that women show a more rapid drop-off of alcohol concentration in breath tests than do men. And as alcohol leaves a person's system, the depressive symptoms go away, causing a state of alertness.

Prior history of alcohol use and peak alcohol levels in the study didn't seem to differ between men and women and so likely weren't the cause of the gender differences, he said.

The findings, which will be published in the May 2011 issue of the journal Alcoholism: Clinical & Experimental Research, and suggests sex should be taken into consideration in future studies on "the relationship between sleep quality and risk for the development of alcohol use disorders, as well as studies evaluating how sleep quality relates to relapse among recovering alcoholic individuals," Arnedt said.

Participants, who were studied at the General Clinical Research Center (GCRC) at the Boston Medical Center, earned up to $450 for study participation.