Drinking water is essential to overall health. H2O accounts for up to 60 percent of the human body, and it helps with a wide variety of bodily functions — from cell growth to waste removal to digestion, according to the U.S. Geological Survey. And yes, hydration can affect sleep, too.
“Being adequately hydrated is essential for ensuring your body functions as it should — and not just during the day,” explains Jackie Newgent, RDN, CDN, a plant-forward culinary nutritionist and author of The Clean & Simple Diabetes Cookbook, who believes that being dehydrated can negatively impact one’s sleep.
However, drinking too much water before bed can also interfere with sleep, notes Vincent Pedre, MD, the medical director of Pedre Integrative Health in New York City and author of Happy Gut. You’re not going to be sleeping soundly during the night if your bladder is waking you up to go, after all.
What Science Says About Hydration and Sleep
There is limited research on the relationship between hydration and sleep. But the evidence so far suggests that there is a relationship between the two, with shorter sleep durations associated with lower hydration status.
Both Newgent and Dr. Pedre point to one large cross-sectional study published in Sleep in February 2019. The data showed that in a group of more than 20,000 American and Chinese adults, those who self-reported sleeping less than six hours on average each night were associated with a higher likelihood of inadequate hydration status (as measured by urine samples), compared with those sleeping eight hours or longer each night. (The researchers were investigating the connection because getting too little sleep and getting too much sleep have both been previously linked to kidney problems.)
The data suggests that hydration and sleep may be related, Pedre says.
On the other hand, one small study published in the Journal of Sleep Research in February 2018 found that dehydration did not affect the amount or quality of sleep in 12 healthy young adults — although the study authors noted that more research is needed on the link between the two.
Other research has found that the bodily produced hormone vasopressin helps prevent dehydration during sleep by increasing water absorption in the kidneys later in the sleep cycle (so that you don’t get dehydrated even when you’re not drinking water during the night), according to an article published in StatPearls in August 2020.
“Vasopressin release increases in the late sleep period to help control hydration status at a time when water intake is not possible and respiratory water loss increases,” explains Pedre. “Disruptions in the late sleep period may lead to dehydration by disrupting the release of vasopressin.”
In other words, shorter sleep durations may actually contribute to dehydration.
Can Dehydration Disrupt Sleep?
While research hasn’t yet answered all of the questions around why hydration affects sleep, experts do know a lot about what can go wrong with sleep when you’re dehydrated (as well as if you drink too much water). “Even minor symptoms of dehydration can negatively impact sleep, due to discomfort,” Newgent says.
Pedre adds that dehydration can cause the following symptoms, which can consequently disrupt sleep:
- Muscle Spasms Dehydration can lead to muscle spasms, making it difficult to fall asleep or potentially waking a person up in the middle of the night. Remember, muscle mass is 76 percent water, according to a study review published in August 2019 in Nutrients.
- Muscle Cramping Muscle cramping is another symptom of dehydration, which can sometimes lead to painful tightening of the calf or foot muscles that may wake someone up in the middle of the night.
- Headaches Headaches and migraine attacks can complicate falling asleep and staying asleep.
- Early Morning Thirst Being thirsty can cause someone to wake up in the middle of the night or early morning.
- Dry Mouth Dry mouth can also cause discomfort that may aggravate sleeping.
Can Drinking Too Much Water Disrupt Sleep?
It’s certainly possible to overdo it on pre-bedtime water intake. “If you drink too much water in the evening, it can disrupt sleep, since you may need to take a trip or two to the bathroom to urinate in the middle of the night,” Newgent says. “There’s even a name for this — nocturia — which can be a larger concern for those who find it challenging to go back to sleep after their bathroom trips.”
Pedre agrees that drinking too much water, primarily late at night or close to bedtime, can negatively impact your sleep. Some older studies (one involving dogs and one involving 14 adult men) have suggested that the kidneys filter more blood while the subject is lying in the prone position (on one’s stomach), which fills the bladder faster and increases urine output, as opposed to being in the supine position (on one’s back, facing up).
Pedre further interpreted the studies to mean that excess water intake close to bedtime may be more likely to cause you to have to urinate sooner than if you had drank the same amount of water at a time of day when you were not lying down. While it should be noted that the research is preliminary, the bottom line, Pedre says, is that “Excess water intake near bedtime is often going to wake you up with a full bladder in the middle of the night.”
So, How Much Water Should You Drink Before Bedtime?
“In my opinion, if you’re working on improving your sleep, you want to hydrate during the day, and try to reduce fluid intake later in the day, especially right before bedtime,” says Pedre. He suggests consuming water over the course of the day, and mostly between meals. (Drinking during meals can dilute stomach acid, which could potentially complicate digestion, he says.)
Pedre says that in addition to water intake, it’s also important to pay attention to other factors that affect hydration throughout the day. Coffee consumption and the amount you sweat can both be dehydrating and potentially deplete your body of essential minerals. But consuming water-dense foods can help you stay hydrated.
Pedre suggests avoiding fluids at least one hour prior to bedtime. “However, if you tend to have a hyperactive bladder or incontinence, it’s best to avoid water starting two to three hours prior to bedtime,” he adds.
If you fall into this category, Pedre advises: “Make sure you’re well-hydrated prior to that.”
When you do drink water late at night, Newgent suggests keeping it to small sips as needed: “So, if you turn out the lights at 11 p.m., make 9 p.m. your ‘small sips only’ start time.”
Other Factors That Can Affect Sleep and Hydration
There are a few other factors that can affect hydration and its relationship to sleep.
- Nighttime Sweating Newgent says that if you tend to sweat at night, you can have a notable amount of “insensible water loss” (lost body fluid that cannot be easily measured), which can contribute to dehydration, according to past research. If you’re a night sweater, she suggests taking steps to make for a cooler sleep environment, such as setting your thermostat to a temperature that’s bedtime-comfortable for you — which is likely cooler than a daytime temp. According to the Sleep Foundation, the ideal bedroom temperature for most people is around 65 degrees F, though it may vary from between 60 to 67 degrees F. For some people, and depending on the local climate, the ideal temperature may be a little higher; you’re aiming for a temperature at which the ambient room feels cool.
- Mouth Breathing Mouth breathers can also experience insensible water loss at night. According to one study, heavy mouth breathers expel 42 percent more water than those who breathe through their nose.
- Caffeine Intake As Pedre mentioned, caffeine can act as a mild diuretic (not to mention a stimulant), which can delay your ability to get deep, restful sleep. The Sleep Foundation recommends cutting off caffeine consumption six hours prior to bedtime. “Pick a mantra if it helps, like ‘go caffeine-free after 5 p.m.’ or ‘nix it six hours before sleep,’” he suggests as a tactic.
- Alcohol Intake Like caffeine, excess alcohol intake can have a slight diuretic effect and disrupt the sleep cycle, leading to poor overall sleep quality, says Newgent. “Try to keep alcoholic beverages to no more than one drink in the evening,” she recommends. This is especially important the older you are, since there is higher risk of dehydration with alcohol use as people age, according to a study published in July 2017 in Nutrients.
Important Notice: This article was originally published at www.everydayhealth.com by Leah Groth where all credits are due. Medically reviewed by Justin Laube, MD.
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