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This is how much water your body actually needs

Water makes up more than half of your body weight, and insufficient water intake is a risk factor for heat stroke, kidney disease, and heart failure. And yet, for something so essential, it’s hard to quantify exactly how much we need each day.

Now researchers from an international research team have come up with an equation to predict how much water our bodies actually use and, by extension, how much we actually need to consume.

You may have heard of the 8×8 guideline: we should drink eight 8-ounce glasses of water every day. But how accurate is that?

A common recommendation says you should drink eight 8-ounce glasses of water a day, but research says that’s an overestimate for most people.
pink omelette / Getty

“The eight glasses a day dogma overestimates most people’s water needs,” said Herman Pontzer, a Duke University professor who worked on the study. Newsweek. “It’s not based on any real evidence, as far as we can tell. It’s more of a marketing slogan that seems to have caught on. pure water. Other beverages also count towards our water intake.”

The US National Academies of Sciences, Engineering and Medicine recommend that men consume 3.7 liters (125 ounces) of water per day, while women are advised to drink 2.7 liters (91 ounces). However, these figures include water consumed through food, which represents at least 20% of your daily water intake.

Our body loses water not only through urine, but also through sweat, feces, evaporation from the surface of the skin, and water vapor in our breath. However, Yosuke Yamada of Kyoto University, who led the study, said the amount of water your body uses, called water turnover, is not the same as the amount you need. consume.

“Drinking water accounts for about half to 40 percent of water turnover,” he said. Newsweek. “We consume water from food, and our body itself also produces water during the process of energy metabolism. If you multiply about 0.4 by water turnover, you may be able to get an answer to how much water you need to drink per day, although it depends on what you eat.”

Water needs also vary from person to person. Pontzer said that on average, men’s bodies use about 4.3 liters of water per day, while women use about 3.4 liters. “But it’s not uncommon for men’s or women’s water needs to vary by plus or minus 1 liter per day,” he said.

Yamada said this variation exists between and within individuals. “The variation in water turnover is incredibly large. The lower limit for adults is around 1.5 liters per day and the upper limit is around 6 liters per day…Even in an individual, if the average air temperature is 30 degrees Celsius, the water turnover is 1.0 liters per day higher than at 10 degrees Celsius.

“One-size-fits-all is a big issue both between and within individuals,” he said.

This is how much water your body actually needs
A file image shows a couple drinking water. On average, men need more water than women.

Yamada and his team measured the water turnover and body water content of 5,604 people aged 8 days to 96 years from 26 different countries. To perform these measurements, participants were asked to drink a small amount of “heavy water”, water that had been enriched with deuterium, the heavy isotope of hydrogen. The deuterium can then be tracked as it passes through the body to calculate the amount of water used.

Researchers have identified a range of different environmental and lifestyle factors that affect water turnover in an individual. “We found that age, gender, height, physical activity level, occupation, athletic status, pregnancy, living altitude, air temperature, humidity, and socio-economic status determine a person’s water replenishment,” Yamada said.

Water turnover was highest for men aged 20 to 30, but for women, water turnover remained at its peak between 20 and 55 years of age. “I think it’s because of the gender differences of aging,” Yamada said. “Many researchers indicate that men have higher muscle mass and physical capacity at their peak, but have a higher rate of decline in muscle mass and physical capacity as they age.”

Using this data, the researchers developed their equation to predict an individual’s water intake, keeping all of these factors in mind:

Water renewal = [861.9 × physical activity level] + [37.34 × fat-free mass in kg] + [4.288 × humidity] + [699.7 × athletic status] + [105.0 × human development index of country of residence] + [0.5140 × altitude in meters] – [0.3625 × age²] + [29.42 × age in years] + [1.937 × temperature²] – [23.15 × temperature in Celsius] – 984.8

The equation was produced to help inform global water access strategies and plan for future water needs. But Pontzer said individuals can rely on more intuitive ways to measure water needs.

“The best way to track the water you need to drink each day is to listen to your body,” he said. “If you are thirsty, drink something, preferably water or another healthy drink.”


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