It’s common wisdom we’ve all heard when sick with a cold or the flu: Drink plenty of fluids. Depending on who you ask, keeping up a steady intake of water, tea, or the occasional Pedialyte will supposedly help you recover faster and ease your symptoms. But at some point—perhaps after your fourth trip to the bathroom—you've probably wondered: Is chugging all this H20 actually helping?
The short answer: yes. And the main reason may not surprise you. “When people are sick with the flu, they lose fluids,” says David B. Banach, head of infection prevention and a hospital epidemiologist at the University of Connecticut. “Often from the high fevers, which can contribute to dehydration.”
Dehydration is also a risk for people who experience vomiting or diarrhea—not surprisingly—as their body expels more liquids. Banach also says people who have the flu tend not to have an appetite either, which may prompt them to forget to eat and drink like they would normally, leading them to drink less overall.
If you're sweating a lot, have diarrhea, or vomiting, Banch says you might want to supplement your water intake with an electrolyte solution such as Pedialyte. But for a more run-of-the-mill cold, it’s best to avoid sugary beverages, says Philip Tierno, a professor of microbiology and pathology at NYU School of Medicine.
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That includes juice. Although orange juice has vitamin C and potassium that can help your immune system, it’s also loaded with sugar, which has inflammatory properties. Instead, Tierno recommends drinking plain water with a squeeze of fresh lemon or orange juice from a wedge to get a splash of vitamin C and more flavor.
Another reason people can get dehydrated during cold and flu season is because those illnesses tend to happen in the winter, when the air is drier. This is especially true when you're indoors and the heat is turned on. This won’t necessarily lead to total dehydration in your body, but it will dry up your nose, eyes, and mouth.
“Those conduits of entry, which are called the mucosal surfaces of the body, have to be rich in fluids,” Tierno says. “They need to be moist to have optimal operation—efficient operation—to protect you from getting ill.” Drinking non-sugary fluids helps your body maintain an adequate production of mucus.
Asking people to increase their fluid intake, however, has little to do with "healing" a cold or flu. Hydration is believed to help your immune system, but there isn’t any hard evidence to really support that, Banach says. In fact, there aren’t any scientific studies that support the idea that increasing fluid intake while sick will do anything beneficial to your body. Aside from the fact that dehydration can make people more sick, over-hydrating won’t necessarily quell symptoms or lead you to getting better faster.
There’s also no one-size-fits-all recommendation for how much people should drink when they're sick. A common belief is that everyone should aim to drink about eight glasses of water per day—roughly 64 ounces—but recent studies have called that target into question, suggesting that much water may not be necessary. When in doubt, it helps to just use common sense: If you're thirsty or if your urine is darker than a shade of pale or light yellow, you should probably have some water, says Edward Bernacki, a physician and executive director of healthcare solutions at Dell Medical School at University of Texas at Austin.
Early signs of dehydration include—obviously—increased thirst, but also feeling weak, not urinating a normal amount, and fatigue. More severe symptoms include confusion, lightheadedness, dizziness, and rapid heart rate. (If you fear you may have serious dehydration, Banach recommends being evaluated in the emergency department in case you need intravenous fluids.)
Of course, you can also overdo it in the other direction: There's such a thing as overhydration, which poses its own unique set of problems—such as dangerously low sodium levels in the blood. But for most people, that's generally not a risk they'll run unless they really overdo it; a healthy adult male would have to drink close to six gallons in a day to risk those kinds of side effects.
Generally speaking, if you're running a fever, it helps to be liberal when it comes to refilling your water glass: Bernacki recommends drinking an additional eight ounces of water than you normally would for every degree of body temperature you have over 98.8 degrees. (Bernacki also subscribes to the idea that 64 ounces of water a day is a good median baseline to shoot for.) It’s also important for people who are at a higher risk of dehydration, such as elderly patients, young children, and pregnant women, to drink plenty of fluids when they are sick—especially if they have a fever or are losing water.
“One of the main reasons why patients get admitted to the hospital in the setting of a flu or a virus infection is for dehydration,” Banach says. “So I think it's really critical to keep up with your hydration status and avoid becoming dehydrated. It's something that any person who becomes sick with a virus, particularly the flu, needs to be aware of.”
Bernacki also says proper hydration can help your body use medication better, which may lead to a quicker alleviation of symptoms. Most of the time, you'll simply want to shoot for drinking six to eight glasses of water a day, increasing that intake if you have a fever, diarrhea, or vomiting. And if you're really losing liquids, replenish your body with an electrolyte-enhanced beverage. It may not make your cold and flu symptoms go away, but it can prevent them from getting even worse.
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