We all know drinking water is important, but a new study shows it may also play a big role in how well you sleep.
Researchers found that even mild dehydration can make it harder to fall asleep and leave you feeling more tired the next day, even if you sleep longer.
The study was led by Professor Elaine Choung-Hee Lee and Professor Emeritus Lawrence Armstrong at the University of Connecticut, along with Ph.D. student Alan Ky and collaborators from Texas Tech University. Their findings were published in SN Comprehensive Clinical Medicine.
The researchers studied 18 healthy college-aged men over four days. On the first day, they checked each participant’s baseline hydration level. On day two, the participants were well-hydrated by drinking 500 milliliters of water the night before.
Then, they were told not to drink anything after their lab visit so they would arrive the next day mildly dehydrated (a condition called hypohydration). On the final day, they resumed normal eating and drinking, and the researchers took more measurements.
The team used several trusted methods to measure hydration, including checking urine color, urine concentration, and body weight changes. The participants also answered detailed surveys about their sleep, including how long it took them to fall asleep, if they woke up during the night, and how rested they felt in the morning.
Interestingly, when dehydrated, participants actually slept about an hour longer than usual. But they reported worse sleep quality—they had more trouble falling asleep and felt more tired the next day.
Because the researchers carefully controlled how much water participants drank and measured their hydration levels, they were able to clearly link hydration to sleep quality.
This study was first designed to understand how hydration and sleep affect athletic performance. But the results apply to everyday life as well. The levels of dehydration studied were mild—similar to what many people experience daily without realizing it.
“You might feel groggy or have trouble sleeping, and it could be related to how much water you’re drinking,” said Lee.
The team also collected blood samples to study how dehydration affects immune system cells. They plan to publish more findings soon and are also interested in studying pregnant women and children, who may be more sensitive to dehydration.
“This study is just the beginning,” said Lee. “We’re now building on it to explore how dehydration affects exercise, heart health, immune function, and other things that are closely linked to sleep.”
So if you’re struggling with falling asleep or waking up feeling tired, your water intake could be part of the problem.
The study is published in SN Comprehensive Clinical Medicine.
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