Can You Get Dehydrated While You Sleep? Here’s What an Expert Says

Updated: Oct. 20, 2017

We spend about a third of every day sleeping and not taking in necessary fluids. How concerned should we be?


To stay properly hydrated, you need to drink water regularly throughout the day. The Institute of Medicine recommends that men should aim for 13 cups (3 liters) of fluid daily while women should get nine cups (a little more 2 liters). But what happens during the seven to eight hours a day we spend sleeping, when we don’t get those fluids?

A medical article published by the journal Sleep Medicine suggested that being dehydrated while you sleep could decrease cognitive performance. The authors from Henri Poincare University in Nancy, France, went on to say this could be more of a problem for people who snore or have sleep apnea, since a different study showed people who breathe through their mouths lose 42 percent more body fluids than those who breathe through their noses. (These are sleep apnea symptoms you might be ignoring.)

Since there was no actual study performed to test this theory, we asked Rebecca Scott, PhD, research assistant professor of neurology at the NYU Langone Comprehensive Epilepsy Center-Sleep Center, for a second opinion. She said sleep won’t likely affect your hydration levels to the point of cognitive impairment, but dehydration is still a major problem to address.

“Most people are not hydrated properly,” she says. “People don’t really think about [drinking water]. They’re drinking coffee, they’re at work, they’re doing a lot of stuff. … I think people are just distracted.” (It’s also not unusual for you to mistake being hungry with actually being thirsty.)

That distraction can cause medical issues. Dehydration can affect your memory, stress levels, attention to detail and tasks, physical and cognitive performance, and mood. Be on the lookout for symptoms like headaches and simply being thirsty. “If you’re thirsty, you know you’re dehydrated. That’s a signal that you’ve already gone beyond the dehydration point,” Scott says.

So what can we do to stay hydrated? To drink more water, Scott recommends intentionally making water part of your day. Keep a water bottle on your desk. Set an alarm every couple hours to get up for a drink. You can even drink sparkling or flavored water if that works as an incentive for you. Also be aware of these sneaky ways you might be making yourself dehydrated and not even know.