Attention insomniacs: Having a nightcap may actually keep you awake at night.

British researchers have found drinking alcohol before bedtime — even in small doses — may help you get to sleep initially, but hinders the ability to stay asleep by interfering with REM (rapid eye movement) cycles that are key to getting a good night’s rest.

"This review confirms that the immediate and short-term impact of alcohol is to reduce the time it takes to fall asleep. In addition, the higher the dose, the greater the impact on increasing deep sleep [initially]," said Irshaad Ebrahim, medical director at The London Sleep Centre, who helped conduct the analysis.

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“This effect on the first half of sleep may be partly the reason some people with insomnia use alcohol as a sleep aid. 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."

The finding, published in the journal Alcoholism: Clinical & Experimental Research, is based on an analysis of more than two dozen studies examining the effects of alcohol on REM and non-REM sleep. A normal sleep pattern typically begins with NREM followed by a very short period of REM slumber. Then, throughout the night, most people alternate between REM and NREM sleep in 90-minute cycles.

According to the new review, alcohol speeds the onset of that initial NREM sleep, but disrupts slumber through the night by delaying the first cycle of REM sleep and decreasing the overall amount of REM. Alcohol also increases “slow-wave sleep” (SWS) — a key phase of NREM slumber — during which the body repairs and regenerates tissues, builds muscle and bone, and strengthens the immune system. But deeper SWS sleep can also lead to sleep apnea and an increased tendency to sleepwalk.

"Dreams generally occur in the REM stage of sleep," Ebrahim said. "During REM sleep the brain is more active, and may be regarded as 'defragmenting the drive.' REM sleep is also important because it can influence memory and serve restorative functions. Conversely, lack of REM sleep can have a detrimental effect on concentration, motor skills, and memory."

Co-researcher Chris Idzikowski, director of the Edinburgh Sleep Centre, added that REM sleep is not only critical to restful slumber but also to mental health.

"In sum," said Idzikowski, "alcohol on the whole is not useful for improving a whole night's sleep. 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."

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