MADISON, Wis. — If staying hydrated is your New Year’s resolution, odds are you’ve heard the recommendation swimming around for years that you need eight 8-ounce glasses of water a day – but new research spills that idea.
“There’s no one number out there for the 300 million Americans to consume,” said Dale Schoeller, a University of Wisconsin-Madison professor emeritus.
Sixty-four ounces per day was the number soaked into our minds for years, but according to Schoeller, it’s not entirely accurate.
“Thirty, 40% comes from the food we eat and not from drinking, per se,” he explained.
“The most surprising thing was when we started to look back at the history of where this number of eight glasses, eight 8-ounce glasses of water to be consumed per day, we couldn’t find it,” Schoeller said, “and we found that old literature on water turnover and all you could put together was that, okay, people misused it, misinterpreted a good scientific number.”
Schoeller was one of 90 researchers involved in a study published in November that tracked water turnover – or the amount of water that goes through the body – globally.
They used what’s called the doubly labeled water method “in which we give water labeled with two safe, stable isotopes: oxygen 18 and deuterium, and those mix with body water pool very quickly and then wash out, and give you a measure of water turnover and CO2 production.”
This was from a pool of more than 5,600 people from 26 countries, with ages ranging from 8 days to 96 years old.
“About the lowest intake of water was about one liter per day and the highest about six liters,” Schoeller said.
The study found that a 20-year-old man weighing 154 pounds in a well-developed country and getting average exercise went through about 3.2 liters of water per day. A woman of the same criteria but weighing 132 pounds would go through about 2.7 liters.
“What it showed is that there’s no one number that applies to everyone,” Schoeller said. “For most of us, we naturally fall into a healthy range of hydration because of the thirst mechanism, which kicks in every time we’re a little dehydrated, and asks us to drink.”
Schoeller wants to stress that of course, water is one of the most important nutrients of the body, transferring oxygen and nutrients into the body and cells, and transporting waste products of the cells to the kidneys.
But don’t flood your system.
“The other end of the spectrum is you can also damage your health,” the professor said. “By drinking too much, you can wash the sodium out of your body and that leads to loss of body function.”
Counting your cups may seem like an easy way to make sure you keep drinking daily, but according to Schoeller, a better way to see how much water your body needs to take in is to check how it looks coming out.
“It’s better to pay attention to the color of your urine,” he said. “It should be a pale yellow or straw-colored. It tells you whether or not you’re drinking enough water or if you need to drink more.”
The study shows what factors contribute to water intake.
For example, people in low-income countries drink more.
“It’s probably because they’re more exposed to the ambient temperature and humidity not living in an air-conditioned building like we do here,” Schoeller said.
Knowing how much water a population in a city goes through makes it easier to send them the right amount when disasters cut off their water supply.
“Here in the U.S. we’ve had some major problems with failures in our water system in major cities,” Schoeller said, “Florida during the floods, Jackson, Mississippi, when the pumps broke down, Houston recently, and now California with the floods again.”
“This study provides a bedrock prediction of what a million or 100,000 people or whatever size city you’re dealing with will need in that region,” he said.
Schoeller’s fellow researcher Dr. Yosuke Yamada believes it can help better prepare for long-term needs and health concerns as the world’s population continues to grow and the climate continues to change.
But the bottom line is if you just have a thirst to improve your health, don’t gulp gallons – instead listen to your body.
“The takeaway is that you don’t need to force water if you’re not feeling thirsty just to meet a magic number that you’ve read about in a magazine or in a newspaper,” Schoeller said.
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