When you think about drinking enough water, it’s usually when you’re sweating during exercise, feeling under the weather, or scorching during a summer heatwave.
But staying hydrated — whether you’re working out or not — is essential for your body to function properly. Water helps regulate body temperature, keeps your joints lubricated, and shuttles nutrients around to all your cells. Every tissue and organ needs water to function properly, which is why sufficient daily fluid intake is essential for good health. It’s also essential for good sleep.
Studies have begun exploring the link between hydration and sleep, and what hydrating well means for sleeping well. Researchers have determined that even being mildly dehydrated when you get into bed can impact your natural circadian rhythm and interfere with your getting a good night’s rest. Further, if you’re dehydrated and not sleeping well, your poor sleep may also worsen that dehydration.
So if you’re cutting back on fluids later in the day to avoid an overnight bathroom break, you may want to rethink your strategy.
How drinking enough water can help your sleep
Though we call it “turning in for the night,” your body hardly checks out while you’re asleep. There’s a lot of restoration and repair going on during the different sleep stages, in your muscles, bones, and even your brain, where your body's glymphatic system flushes neurodegenerating toxins. All of these processes are reliant on water.
“During REM sleep, your brain is consolidating memories and learning; deep sleep is when your body restores chemical balances, recovers, and heals. Because water is so important for every single one of those functions, being dehydrated when you switch off the lights can affect the many complex biological processes your body goes through to restore itself during the night,” says Dr. Brandon Peters, a neurologist and sleep specialist who currently practices at Virginia Mason Medical Center in Seattle.
Have you ever had excruciating nighttime leg or foot cramps, the kind where your calf muscle seizes up, and you can’t seem to massage it out? Nocturnal leg cramps are often a symptom of dehydration — not surprising when you learn that muscle mass is made up of about 76 percent water — and can cause painful awakenings in the middle of the night or make it hard to fall back to sleep.
Headaches that wreck your focus during the day and linger into the evening can also be caused by dehydration. It’s normal to get a headache from time to time; you might even point to stress as the culprit. However, dehydration may be the real reason behind your occasional headache. Most people don’t get enough fluids. When your body is dehydrated, your brain may temporarily contract from fluid loss, pulling away from your skull, which causes pain. Drink up and you may find it will help relieve the discomfort. Of course, feeling thirsty can also wake you up in the middle of the night or in the way-too-early morning hours.
Studies show that dehydration can also affect our naturally occurring levels of melatonin, the hormone that helps regulate our sleep cycle. Chronic dehydration may reduce the amounts of amino acids present. “The essential amino acid called tryptophan is needed for the body to produce serotonin and, in turn, melatonin,” says Peters. “When you’re dehydrated, you may affect the production of melatonin, so you’re less sleepy at night, and have a harder time falling asleep.”
How poor sleep can lead to dehydration
Recently sleep scientists have begun to explore the flip side of the equation — how sleep deprivation may worsen dehydration.
In a 2019 cross-cultural study of approximately 20,000 adults from the U.S. and China, published in the journal Sleep, researchers found that participants who slept six or fewer hours had up to a 59% higher risk of dehydration than those who regularly got eight hours or more. (Dehydration was measured using urine samples.)
The researchers hypothesized that “the findings may reflect the nightly rhythm of a hormone called vasopressin. During sleep the pituitary gland in the brain uses vasopressin to signal the kidneys to retain fluid in the body rather than excreting it through urine.”
“That’s so you don’t get dehydrated during the night when you’re not taking in any fluids,” explains Peters. “Typically, vasopressin is released later in the sleep cycle, so if you’re cutting your sleep short, less of the hormone reaches the kidneys in time to conserve water.”
According to the study’s lead author, the results show that “if you’re only getting six hours of sleep a night, it can affect your hydration status” during the day. In fact, that foggy and fatigued state you find yourself in the next morning (and throughout the day) may be compounded because you’re dehydrated.
How much water should you drink?
Now that you know the importance of staying hydrated, you may be wondering, “How much water should I drink each day?” It’s often said that the “right” amount is eight glasses a day, or that you should drink half your body weight in ounces of water daily. But the reality is that it’s a bit more complicated and there’s no one-size-fits-all answer.
“It’s always good advice to drink as you feel thirsty,” Peters suggests. Four to six cups daily is a good starting point for generally healthy people, but depending on your activity level, how sweaty you get, and the climate and temperature where you live, the right amount for you may vary. If you’re pregnant or nursing, you’ll need to drink extra water to stay hydrated, since your body is doing the work for two (or more).
To ward off dehydration, it’s best to drink fluids gradually throughout the day. An easy way to do this is to have water with each meal, and a full glass with any medications you take. Keep in mind that you’re also getting fluids from water-rich foods such as salads and fruit, as well as other beverages you drink. (Keep reading for some seasonal, hydrating, and nutrient-rich options.)
It is possible to take in too much water. Caution may be needed if you have certain health conditions, such as thyroid disease or kidney, liver, or heart problems. Likewise, you may want to discuss how much water you should drink with your health care provider if you're taking medications that make you retain water, such as non-steroidal anti-inflammatory drugs (NSAIDs), opiate pain medications, and some antidepressants, says Peters. “Drinking excessive water may lead to electrolyte imbalances, including low sodium levels in a potentially serious condition called hyponatremia that may cause seizures, coma, even death.”
If the day slips away with barely a glass of water, don’t chug a day’s worth right before bed: Too many bathroom visits is a good way to ruin a continuous, restful night’s sleep, which kind of defeats the purpose.
Here are five tips for staying hydrated and getting your best rest.
1. Drink water first thing in the morning.
Kick off your day with a big glass (or two) of water. Drink up before heading to the kitchen for your first cup of coffee — it’s hard, we know! We naturally lose fluids and electrolytes overnight through normal respiration, so get a head start on rehydrating. “If you’re a hot sleeper with night sweats, or you mouth breathe, as is often the case with obstructive sleep apnea (OSA), you’ll lose even more fluid during the night,” says Peters. The same goes if you work out in the evening without rehydrating, or if you’ve had a couple of cocktails or glasses of wine late in the evening.
2. Keep a water bottle with you at work.
To make sure you’re getting enough water during the day, keep a water bottle close by for convenience and also to track how much you’re drinking. If you have a 20-ounce water bottle, for instance, it’s easy to do the math. Think about setting an alarm or scheduling reminders to drink up. Maybe when you get up to stretch your legs, make it a point to take a few swigs from your water bottle.
3. Limit soda or other sugary drinks.
Be conscientious about beverages that aren’t water. Limit sodas and juices, but also alcohol and caffeine, which are diuretics. This means they make you pee more, leaving you dehydrated and possibly disrupting your sleep cycle.
4. Include lots of water-rich fruit and veggies in your diet.
Juicy summer fruit like watermelon, cantaloupe, honeydew melon, peaches, and strawberries are 80 to 90% water, as well as rich in vitamins and other nutrients. In the veggie department, lettuce, tomato, zucchini, celery, and cucumbers have high water content, so load up your plate with these seasonal staples. Many of these are also good sources of electrolytes like potassium and sodium — essential for proper hydration.
5. Keep your bedroom cool at night.
All sleep doctors will tell you that a cool room will help you sleep more soundly by enhancing deep sleep. If your bedroom is too hot, you’re more likely to wake up dehydrated. The consensus is a room temperature of between 60 and 67 degrees makes for the most comfortable, peaceful night’s rest.
