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10 Unexpected Things That Can Cause Dehydration

Nutrition experts reveal the unexpected situations that cause dehydration, from gardening to drinking a lot of coffee before exercise.

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Tired fitness woman sweating taking a break listening to music on phone after difficult training. Exhausted Asian runner dehydrated feeling exhaustion and dehydration from working out at gym.Maridav/Shutterstock

What can dehydrate you?

Staying hydrated keeps your energy up and helps you stay mentally focused. Some situations, such as a hard workout or spending time outside in the hot sun, can commonly lead to dehydration. The sensation is likely familiar: Dry mouth, thirst, fatigue, and even dizziness⁠—all signs that tell you that it’s time to reach for water. But, there are also sneaky things that can rob you of fluids. “Dehydration can easily happen to anybody,” says Amy Goodson, RD, in Dallas-Fort Worth, Texas. It happens when your body is losing more fluid than it’s receiving. The problem is, it can sneak up on you quickly, leaving you feeling run down and ill.

Here, registered dietitians reveal unexpected situations where drinking water and increasing your fluid intake should be on your priority list.

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cause dehydration | grandmother and grandson gardening in backyardRonnie Kaufman/Getty Images

Gardening in your backyard

Don’t think that you have to be running 10 miles in the noon sun to suffer the ill effects of heat exhaustion. “If you are not well-hydrated before working in your yard or gardening, you may sweat a lot, which can lead to dehydration,” says Goodson. She’s seen gardening, which we tend not to think of as an especially vigorous activity (but is really considered moderate-intensity exercise, according to the Centers for Disease Control and Prevention (CDC)), leave people sick for a couple of days because of dehydration. In this instance, keep an icy cold water bottle by your side, garden in the early morning hours if possible (when the sun’s rays are less intense), and wear moisture-wicking clothing that will help prevent overheating. (Still, don’t shy away from gardening: Here’s why it’s one of the healthiest things you can do.)

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cause dehydration | protestors raising fists for racial equalityurbazon/Getty Images

Protesting for Black Lives Matter and other causes

If you’re part of a march or vigil—protesting for Black Lives Matter, for example—don’t forget to drink water. Protesting serves up a triple whammy in dehydration, says Goodson: “You’re generally outside for long periods of time in a hot environment and not paying extra attention to hydrating,” she says. The energy and sweat you’re expending can cause problems for you if you don’t stay on top of your water intake, and severe dehydration, which makes you feel awful, could end in a trip to the emergency room, says Goodson.

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cause dehydration | woman exercising outsideKhosrork/Getty Images

Waking up and exercising

It’s unlikely that you’ve spent the night sipping water. So, after you wake up, you’re naturally a little dehydrated since you’ve likely had little fluid for the past six to 12 hours, says Ryan Andrews, RD, principal nutritionist for Precision Nutrition. What you need depends on how you’re exercising. If you’re doing light activity—say, a walk around the neighbourhood first thing in the morning—then a few sips will suffice, he says. If it’s a hard workout in the heat and high humidity, you’ll need a more targeted plan so you don’t quickly dehydrate and impair your body’s ability to cool down, something that will compromise performance. Andrews recommends drinking one to two cups of water 30 to 60 minutes before going out, sip an electrolyte beverage during exercise, and rehydrate post-exercise with a beverage containing carbohydrates, protein, and electrolytes.

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cause dehydration | woman laying in bed with feverBoris Zhitkov/Getty Images

Being sick with a fever (or, yes, Covid-19)

When you have a fever, your body is running at a higher temperature. “You need to drink more fluids,” says Goodson. She points out that a hallmark of a Covid-19 infection is a high fever for a few days—and you’ll need to counteract that by upping your fluid intake. When you’re sick with anything, your appetite is often down, and by not eating you’re also missing out on necessary electrolytes. Right now, it makes sense to drink an electrolyte-containing beverage like Gatorade, says Goodson, or soup. “Soup is saturated with salt, which will help you retain fluid,” she adds. (If you’re wondering if you could have Covid-19, pay attention to these other coronavirus symptoms.)

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cause dehydration | friends at music festival convertKlaus Vedfelt/Getty Images

Attending an outdoor concert or festival

This may not be happening right now for anyone, but it will be in the future. If you’re spending an extended amount of time outdoors and in the heat—even if you’re simply walking around or sitting down—you can still get dehydrated, says Goodson. “Heat can cause some people to feel fatigued, nauseous, and dizzy,” she says. There is also a lot of alcohol sold at concerts and festivals, and if you’re drinking canned hard seltzer all day, you may wrongly assume that you’re staying hydrated, especially if you continually pee a lot. Remember that alcohol contributes to dehydration, so you can’t count it in your fluid plan for the day.

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cause dehydration | hands holding two pills and glass of waterdszc/Getty Images

Taking diuretics

If you have high blood pressure, you might have been prescribed diuretics or “water pills,” which lower blood pressure by helping the body excrete sodium, but also cause you to lose water by increasing urination. However, you also have to be uniquely concerned with the effects of heat and dehydration. If you have hypertension, spending time in a hot and humid environment may affect you more so than the average healthy adult, explains Goodson. “When you become dehydrated, you lose fluid, which makes blood thicker. The result is that it’s more difficult for your heart to pump blood out to your extremities,” she says.

Talk to your doctor. Depending on what type of medication you’re taking, your doctor may recommend ramping up your potassium intake. Fruits and veggies, in general, are rich in potassium—and conveniently, count in your fluid intake, too.

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cause dehydration | woman pouring coffee into mugceciangiocchi/Getty Images

Consuming a lot of caffeine before exercise

Perhaps you’ve heard the good news that caffeine isn’t something that dehydrates you—provided you drink a reasonable amount. The extra fluid it supplies offsets any diuretic effect for the caffeine. When you’re exercising, though, it’s a different thing. “In reasonable amounts, for people not overly sensitive, caffeine may be a useful performance-enhancing supplement,” says Andrews. He warns people that having more than four to five mg of caffeine per kilogram of body weight (2.2 pounds) can be dehydrating. That means someone who is 165 lbs should avoid having more than 300 to 375 mg of caffeine per day, he says.

Make sure to check how much caffeine is in what you’re drinking. There’s a big difference between a six-ounce mug of Folgers coffee (60 to 80 mg) and running to Starbucks to order a grande (16 ounce) with 360 mg of caffeine.

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cause dehydration | runners getting ready for a raceMr.mansuang Suttakarn / EyeEm/Getty Images

Not drinking enough before an athletic event

“Hydration before sports is 100 percent controllable,” says Goodson. That’s unlike during the event. When you work out, many times you’ll sweat more than you take in, and your sweat to sip rate is often not something you can fully micromanage or stay aware of in the moment. (Though you should aim to have a 16- to 20-ounce bottle of fluid every hour, says Goodson.) What you can change is drinking the right amount leading up to the event. The American College of Sports Medicine recommends drinking five to seven mL of beverages per kg of body weight at least four hours before exercise. For a 140-lb person, that’s about 11 to 15 ounces. Also, eating something with salt (like a piece of toast) will help your body maintain fluid.

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cause dehydration | close up of woman's sweaty shoulder outside during exerciseMoMo Productions/Getty Images

Not being heat acclimated

If you’re used to working out in the heat, then your body is acclimated to functioning at higher temperatures. “People who exercise a lot and are used to functioning in a hot environment typically have good blood flow. They’ve trained their body to function during bouts of intense sweating and heat, and they also might be more cognizant of their hydration needs,” Goodson explains. On the other hand, if you’re used to hoofing it in a climate-controlled place (like a gym) or are in a colder climate and vacation in a hotter one, your body is not ready for the heat. This is the time to have a water bottle on hand at all times so you don’t miss an opportunity to sip. Stop activity if you notice signs of dehydration like a dry or sticky mouth, muscle cramps, headache, or dry skin.

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situations that cause dehydration | close up of cyclist holding water bottleMaria Fuchs/Getty Images

Not adjusting for the weather

You might naturally reach for your water bottle more in the heat, and that’s a good thing. What you might not know is just how much your fluid needs go up in the heat—especially when you’re exercising in the middle of the day when the sun is the strongest. At a temperature of 59 degrees Fahrenheit, a very active person needs four litres of water, says Andrews. At 95 degrees Fahrenheit? “That same [very physically active] person will need 10 litres of water for the day,” he says. (One litre is 33 fluid ounces.)

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situations that cause dehydration | woman walking and exercising in natureIgor Alecsander/Getty Images

How to determine how much water to drink

Goodson recommends setting a goal so that you have something concrete to work toward during the day, to ensure you’re getting what you need. Take your weight in pounds and divide it by two. The result is the number of ounces you need, she says. If you are outside in the heat for sustained exercise and heavily sweating, then it’s likely you need to replace electrolytes, too. In this case, it’s OK to drink something like a sports beverage, even though it contains sugar (which will replace glycogen that you’re burning) and sodium (to replace the salt you’re sweating out.)

Now that you’ve learned about the unexpected situations that cause dehydration, read up on the sneaky ways summer can make you sick.