New Wearable Data Reveals the Scary Truth About Your Overnight Recovery After a Night of Drinking

It's pretty obvious what a heavy night of drinking does to your body when you wake up the next day with a headache, extreme thirst, and nausea that feels like it may never end. But a couple of drinks at dinner can't be that bad, right? A new study published in PLOS Digital Health pulled data from nearly 21,000 WHOOP members to see what alcohol actually does to overnight recovery. 

Researchers looked at over 5 million days of data and found that even a modest amount of alcohol caused resting heart rates to climb and heart rate variability (a sign of how well your body handles stress) to drop. It also led to shorter nights of sleep and less physical activity the next day.

Here's what the data and the experts say is happening inside your body, and what you can do about it if you still want to enjoy a drink.

What One Drink Actually Does Overnight

The study used a within-person design comparing each person’s drinking nights to their sober nights, which means each WHOOP member acted as their own control (something a lot of traditional alcohol research doesn't do).

"Instead of comparing different people to each other…we compared people to themselves," explains Greg Grosicki, PhD, Staff Research Scientist at WHOOP and lead author of the study. By doing this, they could see how alcohol impacts people without age, fitness, or sex muddying the results.

They were able to draw a clear line showing that the more you drink, the higher your heart rate climbs while you sleep, and the more your recovery markers tank. Plus, you end up sleeping less and moving around less the next day. 

Grabbing just one more drink than usual caused sleeping heart rate to jump by about 2.8 beats per minute for women, and 2.4 for men, while heart rate variability dropped 3.8 ms in women and 3.3 ms in men. These numbers show something pretty telling, as Grosicki explains, "a higher RHR and lower HRV represent a shift toward a sympathetic state or our 'fight or flight' response," he says. "Instead of relaxing during sleep, our body is working harder, which is why we wake up the next day feeling tired and less rested."

In general, out of everything the researchers tracked, heart rate variability took the biggest hit. Grosicki pointed out that just a couple of drinks can drop it by 20 to 30 percent, and the more you drink, the worse it gets. And these results are nothing new. Previous research has shown much of the same.

Related: Longevity Specialist Shares the 3 Things He Does for Better Sleep

Why Sleep Feels Fine but Recovery Tanks

Plenty of guys swear a nightcap helps them fall asleep faster, but the wearable data and sleep specialists make it obvious that it doesn't necessarily play out well the next day.

"Eight hours sleeping after a night of heavy drinking is not eight hours of recovery," says Eric Zhou, PhD, Associate Professor at Harvard Medical School's Division of Sleep Medicine. Alcohol is a central nervous system depressant, so it can knock you out fast, then shred the architecture of your sleep as your liver works through it.

"Alcohol is a sedative, not a sleep aid," says Funke Afolabi-Brown, MD, a triple board-certified sleep medicine physician. She explains that alcohol suppresses REM sleep (the dream-heavy stage tied to mood and memory) in the first half of the night and reduces deep sleep, which "limits the ability of the body to get the reparative benefits of sleep, such as hormonal repair, memory consolidation, muscle recovery, and improved metabolism."

She adds that alcohol can also make snoring and sleep apnea worse, piling on more daytime fatigue.

Carlos Nunez, MD, Chief Medical Officer at ResMed, says it's about brain chemistry. Alcohol boosts GABA, a calming neurotransmitter that acts like a sedative, pushing you into non-REM sleep early in the night. As your body processes the alcohol, that effect reverses, and sleep becomes lighter and more fragmented. You'll wake up multiple times a night, but fall back asleep so quickly you won't remember them, which is why you can swear you slept through the night and still feel wrecked in the morning.

Related: Why Your Last Hour of Sleep Might Be the Most Important, According to a Top Sleep Scientist

Women and Younger Drinkers Take the Bigger Hit

The study found that alcohol doesn't impact everyone the same way. Women generally experienced more significant disruptions than men, even when accounting for differences in body size. Younger adults also saw a more negative impact on their recovery markers compared to older people.

Women are likely more impacted by alcohol due to their physiology. They typically have less water in their bodies to dilute the alcohol and fewer enzymes in the stomach to break it down before it hits the bloodstream. So, even with the same number of drinks, women often end up with more alcohol in their systems than men.

When it comes to age, Grosicki explains that younger people's bodies are more sensitive to the stress of alcohol, which is why they see bigger dips in recovery. On the other hand, older people's bodies might already be stressed more regularly, making the sudden spike from alcohol feel less dramatic.

Habits That Can Soften the Blow

Here's where you can breathe a sigh of relief, because you don't necessarily have to completely give up your favorite drinks. The research found that making some tweaks to how and when you drink can help you bounce back after partaking a bit too much.

One of the best ways to help yourself is to drink earlier in the day. Imbibing about two hours earlier in the evening, like a pre-dinner drink rather than after dinner or a nightcap, was linked to lower resting heart rate and higher heart rate variability during sleep. Getting more sleep than usual after drinking and going easier on exercise that day also reduced the physiological hit.

Zhou recommends thinking about damage control going in. "Drink less (even one fewer drink can matter), and finish earlier, being fastidious about avoiding alcohol leading up to bedtime."

Brown suggests finishing your last drink at least three hours before bed and hydrating through the evening so your body has time to process the alcohol before you lie down.

Here are a few tips from the data and experts:

• Cut yourself off early: Stop drinking at least three hours before hitting the hay to give your liver a head start.
• Sleep in the next morning if you can: If you partied late, sleep in. Extra rest helps buffer the spike in your heart rate.
• Don't try to sweat it out: The research showed that when your body is already stressed, a brutal gym session will only dig you into a deeper recovery hole.
• Hydrate with a deadline: Drink water while you imbibe, but stop an hour before bed so you aren't waking up for bathroom trips.
• Less is always more: Even skipping just one round significantly improves recovery data.

Related: Sleep Experts Say This Is One of the Biggest Reasons People Wake Up Tired