It’s totally normal to feel crappy after a night of tossing and turning or staying up too late. But new research suggests that there may be more than just sleep deprivation to blame: You may also be dehydrated, researchers say, and drinking more water may help you feel better.
The study, published this week in the journal Sleep, found that people who reported regularly sleeping just six hours a night were 16 to 59% more likely to be “inadequately hydrated” (based on analyses of their urine samples) than those who said they normally slept eight. Both United States and Chinese adults participated in the research—about 25,000 people in all—and the results were consistent across both populations.
That doesn’t mean that people who sleep less also drink less; in fact, the study authors actually controlled for total fluid consumption among some of the participants. They found that even when people reported drinking the same amount, those who slept less were more likely to have more concentrated urine and other signs of dehydration.
So what’s going on? The study authors say it likely has to do with a hormone called vasopressin, which helps regulate the body’s hydration status.
Vasopressin is released both day and night, but production really ramps up later on in the sleep cycle, said lead author Asher Rosinger, assistant professor of biobehavioral health and anthropology at Penn State University, in a press release. “So, if you’re waking up earlier, you might miss that window in which more of the hormone is released, causing a disruption in the body’s hydration,” he added.
The authors point out that poor sleep has been associated in previous studies with chronic kidney disease, and they say that dehydration may be a significant driver of that link. Long-term dehydration can also raise a person’s risk of kidney stones and urinary tract infections, as well.
Because the study relied on self-reported sleep data and only looked at urine results at one point in time, it was only able to find an association between the two—not a cause-and-effect relationship. Future studies should look at this relationship over the course of a week, the authors wrote in their paper, to understand how people’s hydration and sleep statuses change daily.
The National Sleep Foundation suggests that adults should get seven to nine hours of sleep a night and that it’s best to keep your bedtime and wake-up time as consistent as possible. (In this study, sleeping more than nine hours a night did not seem to have any effect, in either direction, on hydration status.)
Of course, you really don’t need another reason why skimping on sleep is bad for you: It’s also been linked to a higher risk of cardiovascular disease, overeating, weight gain (even when it’s not linked to overeating), and diabetes, to name a few. It can also cause short-term problems, like irritability, difficulty concentrating, memory problems, and drowsy driving.
But dehydration itself has also been shown to cause headache and fatigue and to affect mood, cognition, and physical performance—which may be adding onto the already negative effects of a sleepless night, the authors say. “This study suggests that if you’re not getting enough sleep, and you feel bad or tired the next day, drink extra water,” Rosinger said.
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