Science Reveals How Even Just 2 Alcoholic Drinks Can Mess With Your Sleep

A fascinating study in 2011 pointed out that when it comes to drinking and sleep, time is a seriously important factor. "With alcohol given close to nocturnal sleep time, studies find a reduction of sleep onset latency" — meaning, a reduction in time it takes to fall asleep — "and reduced REM sleep," the scientists wrote. The closer to your bedtime you have your two drinks, the less time it may take you to fall asleep, but the more your REM sleep will suffer later on.

Time of day also mattered. The study found that drinking alcohol at 4 a.m. increased the amount of time people spent awake and reduced the time they spent in stage 2 sleep, one of the first sleep stages. Drinking at 10 a.m., 4 p.m. or 10 p.m., by contrast, didn't affect sleep in the same way, so it's worth cutting out the "final drink before you go" if you're out on the town in the early hours.

A study in Neurology in 2018 found that people who drank moderately or heavy — meaning two drinks a night or more — had a much higher risk of disturbed REM sleep than people who had lower alcohol intake. Compared to people who didn't drink at all, drinkers had 23 percent more risk of having REM problems.

That matters because REM is seriously important to restful sleep and brain function. At night we cycle through stages of sleep, from lighter sleep to deeper sleep and finally to REM, which is the stage where we dream. We know that REM sleep is linked to memory and retaining information, and disruptions in its cycles mean we're causing issues for our cognition when we're awake.

Beyond REM sleep, two drinks can disrupt your brain activity during sleep in other ways. "Drinking alcohol before bed is linked with more slow-wave sleep patterns called delta activity," wrote the National Sleep Foundation. "That’s the kind of deep sleep that allows for memory formation and learning. At the same time, another type of brain pattern — alpha activity— is also turned on. Alpha activity doesn’t usually happen during sleep, but rather when you’re resting quietly. Together the alpha and delta activity in the brain after drinking may inhibit restorative sleep."

We experience delta activity from stage 2 sleep onwards, but particularly in stage 3, where we're not yet dreaming but are in a deep sleeping state. Alpha activity shouldn't occur during sleep at all, but after two drinks, a study revealed in 2006, young women in particular see more alpha waves in their brains.

While two drinks' worth of alcohol may help you fall asleep eventually, it has ripple effects throughout the rest of your night's sleep. Sleep has its own "architecture": an internal structure that has to happen for you to wake up feeling rested. Scientists wrote in the Handbook Of Clinical Neurology in 2014 that alcohol before sleep "leads to decreased sleep onset latency and changes in sleep architecture early in the night, when blood alcohol levels are high, with subsequent disrupted, poor quality sleep later in the night."

We've known about the impact of alcohol on the time it takes to fall asleep for a while. Irshaad Ebrahim of the London Sleep Center told TIME in 2013 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.” Basically, you may crash fast, but later on your sleep will become more fragmented and less restful, and you'll likely wake up a lot or get up in the morning feeling kind of wrecked.

Drinking before bed can relax the muscles around your mouth and throat, because of the relaxing quantities of alcohol, and that increases the risk of snoring, according to science. Alcohol-induced snoring is usually more likely in men than women, though, for reasons that aren't entirely clear, but a study in 2006 found that young Swedish women with low BMIs were more likely to snore if they had alcohol before bed.

Yale University sleep expert Dr. Meir Kryger writes in The Mystery Of Sleep that moderate alcohol consumption before bed can also exacerbate the effects of sleep apnea, where the airways are temporarily blocked while you sleep. That's backed up by a study in 2018 that reviewed 21 experiments over 30 years, between 1985 and 2015, and found that obstructive sleep apnea was more likely in people who drank moderate or heavy amounts of alcohol.

Two drinks before bed might not seem like a huge amount, but it turns out that your sleep is quite sensitive when it comes to your alcohol intake. To be safe, drink earlier in the day, or stick to one drink more than an hour before you hit the hay.