It seems even if you drink enough to pass out, you are still in for a rough night of sleep.  Scientists have found that people who drink alcohol before sleep go on to have more disturbed sleep later than the average person lying in rest.

Reviewing 20 studies that included 517 participants who were tested in 38 sleep laboratory experiments, the researchers have determined the disturbed sleep patterns are strongly correlated to imbibing, and the passing out that occured when subjects of the studies were overly drunk.  Volunteers drank varying amounts of alcohol, ranging from a low of one or two drinks, a moderate amount of two to four drinks, to a high amount of four or more drinks.  Most participants were health young adults that did not have drinking problems, and the experiments looked at one night drinking as well as consecutive nights of drinking.

"This review confirms that the immediate and short-term impact of alcohol is to reduce the time it takes to fall asleep," lead author of the study Irshaad Ebrahim, director of the London Sleep Center, said in a statement. "In addition, the higher the dose, the greater the impact on increasing deep sleep."

This explains why so many people rely on alcohol to help them fall asleep, despite warnings that it can actually worsen insomnia.  "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," Ebrahim says.

That presents a more complicated picture of how alcohol affects sleep, and may have implications to scientists' understanding of how sleep can impact overall health.  In all doses studied, alcohol increased deep or slow-wave sleep (SWS) during the first part of the night.  This type of sleep is associated with healing and regeneration of bones, muscles and other tissues, as well as maintaining a strong immune system.

"SWS or deep sleep generally promotes rest and restoration," Ebrahim says cautioning,  however, that alcohol increases in this stage can worsen sleep apnea and sleepwalking in people who are prone to those problems.

However, drinking is already known to reduce REM sleep, the deepest sleep stage where dreams occur, and it is thought during this sleep memories are likely stored and learning occurs.  According to the study, one or two drinks can increase slow-wave sleep while not affecting the deeper REM sleep.  But more alcohol can disturb your REM sleep too.

What does this mean for party goers everywhere?  It seems one or two drinks may help you fall asleep faster, but a night of drinking until you pass out will ultimately leave you restless.  Like so many things in life, moderation with your alcohol consumption could be the key to getting a good night's sleep.