How much water do people actually drink per day?

The common belief that eight, 8-ounce glasses of water a day is enough to meet a person’s daily needs has been debunked by a new study involving thousands of participants. The results show that people’s water consumption varies widely around the world and throughout their lives.

According to co-author Dale Schoeller, a longtime researcher of water and metabolism at the University of Wisconsin-Madison, “the science never really supported the old eight-glass thing as an appropriate guideline, just because it confuses water from beverages with the overall water cycle. And most of your water comes from the food you eat.” “.

The author adds: “But this work is the best we’ve done yet to measure how much water people consume on a daily basis—the cycle of water in and out of the body—and the key factors that drive that cycle.” .

This does not mean that the new results establish a new rule. For the study, published today in the journal Science, the water cycle of more than 5,600 people from 26 countries, aged 8 days to 96 years, was assessed. The results showed that the daily average water circulation varies from 1 to 6 liters.

The author adds: “There are those who convert up to 10 liters of water per day.” “Variability means that pointing to an average doesn’t tell you much. The database we’ve put together shows us big things about differences in the water cycle.”

Previous studies of water cycling have largely relied on volunteers who recalled and self-reported water and food consumption, or focused on their questionable use as representative of the majority, such as a small group of young, male soldiers working outdoors in desert conditions. of people.

By tracking the circulation of “labeled water,” the new study was able to calculate how long it took for the water to pass through the bodies of study participants. Participants drank standardized amounts of water containing radioactive isotopes of hydrogen and oxygen.

Isotopes are atoms of the same element with slightly different atomic weights, allowing them to be distinguished from other atoms of the same element in a sample.

“If you measure the rate at which a person excretes these stable isotopes in their urine over the course of a week, the hydrogen isotope can tell you how much water they’ve replaced, and the elimination of the oxygen isotope can tell us how many calories they’ve consumed. burns,” Schoeller explains.

The study, which included more than 90 researchers, was led by a team that included John Speakman, professor of zoology at the University of Aberdeen in Scotland, and Yosuke Yamada, a former postdoctoral researcher in Schoeller’s lab at the University of Wisconsin-Madison. and current division head of the National Institute for Biomedical Innovation, Health and Nutrition in Japan. They collected and analyzed participant data by comparing measured water cycle, energy expenditure, body mass, sex, age, and athlete status with environmental characteristics, including temperature, humidity, and elevation of the participants’ hometowns.

The group also considered the Human Development Index (HDI), a composite indicator of a nation that combines economic, educational and life expectancy data.

In the study, men’s water cycle volume peaked in their 20s, but women’s water cycle volume remained stable between the ages of 20 and 55. However, neonates had the highest proportion of daily water, regaining approximately 28% of their body weight each day.

Differences in water circulation were first explained by gender, then by Human Development Index and age, and finally by the level of physical activity and athleticism of the person.

All else being equal, there is about a 0.5 liter water cycle difference between men and women. Initially, the study results show that a 20-year-old, 70-kilogram (154-pound) non-athlete male with moderate physical activity lives at sea level in a developed country with an average temperature of 10 degrees Celsius (50 degrees Fahrenheit) and 50 % relative humidity consumes and loses about 3.2 liters of water per day. In the same environment, a 60 kg (132 lb) woman of the same age and activity level would drink 2.7 liters (91 oz) of water each day.

If a person’s energy consumption doubles, their water cycle is predicted to increase by about one liter per day. An additional 50 kg adds 0.7 l/day. For every 50% increase in humidity, water consumption increases by 0.3 liters. Athletes drink about a liter more than non-athletes.

The researchers found that “hunter-gatherers, mixed farmers and agriculturalists” use more water than people living in industrialized economies. Overall, daily water use rises in direct proportion to a country’s HDI rating.

“It represents a combination of several factors,” adds Schoeller. “People in low HDI countries are more likely to live in areas with higher average temperatures, more likely to engage in physical labor and more likely to be indoors during the day in a climate-controlled building. This, in addition to the fact that they have little access to a sip of clean water when they need it, increases their water cycle even more.”

According to Schoeller, the data will allow for more accurate predictions of future water demand, which will be especially useful in emergency situations.

“Look at what’s happening in Florida or Mississippi right now — all those regions are suffering from water shortages,” he said. “The better we understand how much they need, the better prepared we are to respond to an emergency.”

Experts believe it will help us plan better for the future and deal with any urgent health issues.

“Determining how much water people consume is of increasing importance due to population growth and increased climate change,” adds Yamada. “Because water turnover is related to other important indicators of health, such as physical activity and body fat percentage, it has potential as a biomarker for metabolic health.”

Source: 10.1126/science.abm8668

Image credit: Joshua Roberts/Getty Images