When you get a virus or infection, your first instinct may be to drink lots of water or hot tea; after all, we’ve all heard the advice to stay hydrated when you’re sick. But doctors at Kings College Hospital in London are warning against downing too many fluids during an illness, after a patient did just that—and developed potentially fatal water intoxication.
The woman, a 59-year-old with a recurring urinary tract infection, was admitted to the hospital after becoming shaky, vomiting several times, and developing significant speech difficulties. Tests revealed that she had hyponatremia, a condition that occurs when the level of sodium in a person’s blood is too low, due to excessive fluid consumption.
Once doctors realized what was happening, the woman admitted to drinking several liters of water that day in an attempt to help treat her UTI. She said she’d been advised, during a previous infection, that drinking plenty of fluids would help to “flush out her system.”
Doctors Laura Christine Lee and Maryann Noronha described this cautionary tale in the journal BMJ Case Reports, writing that there’s actually very little evidence for this type of advice. In fact, there’s little proof that drinking lots of water during any type of illness is particularly helpful. For example, they wrote, one large medical review found “no evidence for or against increased oral fluid intake in acute respiratory infection.”
The woman improved after doctors restricted her fluid intake over the next 24 hours, but she was lucky: Hyponatremia, or water intoxication, is a medical emergency: People whose sodium levels drop below 125 mmol/L (like this woman’s had) have about a 30 percent chance of dying.
If you’ve heard of hyponatremia before, it was likely in the context of endurance athletes, like marathoners and Ironman triathletes, who are working out and sweating—and drinking water—for several hours on end.
But this isn’t the first time the condition has been blamed on that old advice to drink fluids while sick: The authors of the case report also mention another case in which a woman died from hyponatremia after drinking an excessive amount of water during an episode of stomach flu.
Drs. Lee and Noronha do note that it’s extremely uncommon to develop water intoxication in a non-exercise setting, especially when a person has normal kidney function. And Anar Shah, M.D., an emergency medicine doctor at Mount Sinai Hospital in New York City, agrees that it’s something most healthy people will never have to worry about.
“I think it’s an interesting report for sure, but I think that it falls on the more extreme end of the spectrum,” Shah tells RealSimple.com. And, she says, there are plenty of legitimate reasons doctors recommend staying hydrated.
It’s common to lose more fluids than normal when you’re sick, says Shah—from vomiting, diarrhea, or (if you have a fever) sweating, for example. “On top of that, your metabolism may be sped up and your body’s at an increased level of activity,” she says. “You may require additional hydration to keep your fluid levels balanced.”
Not getting enough fluids can affect the body’s ability to fight infection, she says, and people who are ill may not notice subtle signs of dehydration including dry lips, dry skin, headaches, fatigue, and decreased urination. They may also not feel up to eating or drinking as much as they normally do.
However, she adds, the concept of “flushing out an illness” isn’t accurate. “It’s more to rebalance your electrolytes and blood volume, rather than to directly affect the infection or treat the problem itself,” she says. “Using that language gives people the wrong idea of what hydration is doing for them.”
In their case report, Lee and Noronha point out that some illnesses can drive up levels of antidiuretic hormones, which reduce the body’s excretion of water—and could, theoretically, lead to dangerously diluted sodium in the blood. For these types of conditions, the physicians say that maybe guzzling water shouldn’t be recommended. “Are there potential risks of this apparently harmless advice?” they asked.
Shah agrees that this is a real possibility—but says those cases are few and far between, and should be discussed between doctors and patients at the time of diagnosis.
For most people, she says, aiming for eight 8-ounce glasses of water a day is a “good standard” whether you’re sick or not, and increasing that amount slightly while you’re not feeling well or fighting an infection probably isn’t a bad idea. (The eight-glasses-a-day advice isn’t exact science, but many experts still say it’s a good goal to aim for.)
“People should practice moderation and use their judgment,” she says. “You want to give your body what it needs to heal and combat your illness. Focus on maintaining your normal fluid intake and replacing what’s been lost, but don’t go overboard and drink multiple gallons of anything.”
This article originally appeared on RealSimple.com.