Alcohol's Impact on Sleep Revealed in Nightcap Warning

A glass of wine with dinner or a quick drink before bed can be a tempting way to relax and unwind after a long, stressful day. But, according to scientists, these twilight tipples are probably doing more harm than good.

While a nightcap might help you fall asleep faster, alcohol has been shown to disrupt our natural sleep cycle, suppressing REM sleep in the first half of the night and increasing light sleep and wakefulness in the second half.

"REM sleep, or rapid eye movement sleep, occupies about 20 percent of a typical night's sleep, increases across the night, and is the state of sleep from which dreams most commonly arise," Jared Saletin, a professor of psychiatry and human behavior at Brown University, told Newsweek. "While its exact functions are unknown, REM sleep has been linked to emotional regulation and mental health, as well as memory processing, and creativity. Decreased or altered REM sleep may have detrimental impact on these aspects of our lives."

Katie McCullar, a post-doctoral fellow in neurology at Harvard Medical School who recently completed her Ph.D. at Brown University, added: "REM deficit has been associated with learning and memory impairment and mood disturbances to name a few."

"We are still exploring the full range of effects that REM sleep deficit may cause," she told Newsweek.

In a recent study, published in the journal Sleep, McCullar, Saletin and their colleagues at Brown explored the effects of alcohol on the structure of our sleep, and how this effect can accumulate over time.

To explore these effects, the team recruited 30 adult participants to spend three consecutive nights hooked up to a brain activity monitor while they slept. The experiment was repeated twice for each individual, but each time they were given a different pre-bed beverage. In one experiment, they were given a mixer; in the other, alcohol plus that same mixer, one hour before lights out.

"Our study was novel in its repeated night design," Saletin said. "We found it interesting that the changes to sleep persisted across multiple nights when each was preceded by a drinking episode. Sleep did not seem to 'adapt.'"

In line with previous studies, alcohol before sleep was associated with a significant, cumulative decrease in REM sleep.

Indeed, according to the Sleep Foundation, even low amounts of alcohol—that is less than two drinks for men and less than one drink for women—can decrease sleep quality by up to 9.3 percent.

"Our study explored relatively low levels of alcohol (targeting the legal limit of 0.08) and still discovered quite an effect," McCullar, the study's first author, said.

Saletin added: "We do not know if there is a safe amount to drink without altering sleep. This is an important next question to answer. Future studies should consider how these effects are impacted by consumption rates which include those considered 'under the legal limit.'"

Of course, this does not mean that your sleep cycle will be destroyed after a single, one-off drink on a Friday night. "Although our study indicates that alcohol impacts sleep architecture, it is important to note that the brain has the ability to compensate for a night or two of bad sleep, so a drink or two every now or then is (most likely!) okay," McCullar said.

The team hope that their research will help inform public health signaling about the effects of drinking before bed. "Sleep is critical for so many aspects of our mental and physical health," Saletin said. "I hope this study draws attention to how our daily habits, like the common act of drinking in the evening, may alter sleep in meaningful ways. I hope our work helps individuals stay mindful of getting a good night of sleep."

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