Since you live in a body that consists of up to 60 percent water1, it only makes sense that hydration is essential to good functioning and all-around good health—sleep health included. The relationship between sleep and hydration is complex: It turns out that not only is good hydration important for healthy sleep, but healthy sleep is probably important for good hydration as well.
Several factors can cause you to lose water as you sleep.2 You’ll gradually dehydrate through normal breathing, especially if you’re snoring or breathing through your mouth instead of through your nose. If your room is too warm, or if you’re getting overheated for hormonal reasons, you may lose water through sweat. Or you may be dehydrated from drinking alcohol or doing vigorous exercise too close to bedtime.
Here’s how sleep and hydration are interrelated, and some tips for hydrating for better sleep.
How hydration affects sleep
Even mild dehydration at night can disrupt your sleep. It can cause your throat and nasal passages to get uncomfortably dry, setting you up for snoring. Or your sleep may be fragmented because you wake up thirsty, with a headache or with leg cramps.
Consider, too, that dehydration impedes your brain’s serotonin production,3 which can cause an increased heart rate, stress and symptoms of anxiety—all of which make it much more difficult to settle down for some quality rest.
How sleep affects hydration
A study published in 2018 suggested that the sleep-hydration relationship goes both ways.4 These researchers found that people who slept six hours per night or less had more concentrated urine than those who got a full eight hours of sleep.
Researchers said one likely cause has to do with an antidiuretic hormone called vasopressin, which helps to maintain the water content of tissues in the body. Vasopressin is released soon after we fall asleep and again late in the sleep cycle. But people who wake up too early might be missing the second window when this water-balancing hormone is released, setting themselves up for dehydration during the day.
How to break the dehydration cycle
Good hydration is just one factor that contributes to quality sleep, but it’s one worth addressing: Poor hydration5 and poor sleep6 can both make you feel fatigued, brain-fogged and generally lousy during the day, as well as contribute to chronic health problems.
Here’s “Sleep Doctor” Michael J. Breus’ advice7 for improving both:
- Count backward eight hours from the time you need to get up, and stick to that bedtime every day.
- As soon as you wake up, drink a glass or two of water, and wait at least 90 minutes before having a cup of coffee (it’s a diuretic). Also, stop drinking caffeinated beverages by 2 p.m.
- Avoid alcohol (another diuretic) three hours before bed, and drink a glass of water for every alcoholic drink you have.
- Exercise every day, and be sure to replace the sweat you lose.
- Drink your water in front of a window to get the sunlight that tells your body it’s morning.
Consider setting alarms to help you remember to drink water throughout the day—and be sure to front-load it. If you try to “catch up” by drinking several glasses right before bed, you might find your sleep interrupted for a different reason: having to get up to use the bathroom.
- “The Water in You: Water and the Human Body,” United States Geological Survey.
- “The Connection Between Hydration and Sleep,” National Sleep Foundation,” updated July 2020.
- “Water, Depression, and Anxiety,” Solara Mental Health.
- “Sleep deprivation may cause dehydration,” Medical News Today, November 2018.
- “Acute and chronic effects of hydration status on health,” Nutrition Reviews, September 2015.
- Sleep Disorders and Sleep Deprivation, Chapter 3: “Extent and Health Consequences of Chronic Sleep Loss and Sleep Disorders,” edited by Harvey R. Colten and Bruce M. Altevogt, Institute of Medicine Committee on Sleep Medicine and Research, 2006.
- “The Relationship Between Water And Sleep Is A Two Way Street – How To Avoid Dehydration,” The Sleep Doctor, February 2019.