A new study of thousands of people reveals a wide range in the amount of water people consume around the world and throughout their lives, definitively putting to rest the oft-repeated notion that eight 8-ounce glasses meet daily needs. of the human body.
Human water requirements Water requirements for human consumption may become more difficult to manage as changes occur in the Earth’s climate and human populations. Yamada et al. used an isotope labeling technique to track water intake and loss in individuals in a wide range of environments and living conditions. Total water intake and output varied depending on many factors, including body size, physical activity, air temperature, humidity, and altitude. The authors derived an equation to predict water use based on these parameters. Summary Water is essential for survival, but one in three people worldwide (2.2 billion people) lack access to safe drinking water. Water intake requirements largely reflect water turnover (WT), the water used by the body each day. We investigated the determinants of human WT in 5604 individuals aged 8 days to 96 years from 23 countries using isotope tracking (2H) methods. Age, body size, and composition were significantly associated with WT, as were physical activity, athletic status, pregnancy, socioeconomic status, and environmental characteristics (latitude, altitude, air temperature, and humidity). People living in countries with a low human development index (HDI) had higher WT than people in countries with a high HDI. Based on this extensive data set, we provide equations to predict human WT in relation to anthropometric, economic, and environmental factors. |
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“Science has never supported the old eight-glass thing as an adequate guide, if only because it confused total water renewal with water from drinks and much of the water comes from the food you eat,” says Dale Schoeller , from the University of Wisconsin. –Madison professor emeritus of nutritional sciences who has been studying water and metabolism for decades. "But this work is the best we’ve done so far to measure how much water people actually consume on a daily basis, water turnover inside and outside the body, and the main factors that drive water turnover."
That doesn’t mean the new results fit a new guideline. The study, published today in the journal Science, measured the water turnover of more than 5,600 people from 26 countries, ranging in age from 8 days to 96 years, and found daily averages ranging between 1 liter per day and 6 liters per day.
“There are also outliers that are generating up to 10 liters per day,” says Schoeller, co-author of the study. “Variation means pointing to an average doesn’t say much. “The database we’ve put together shows us the important things that correlate with differences in water turnover.”
Previous studies on water renewal have largely relied on volunteers to recall and self-report their water and food consumption, or were focused observations, of, for example, a small group of young soldiers working outdoors in conditions desert, of questionable use as a representative of the majority of the people.
The new research objectively measured the time it took for water to move through the bodies of study participants following the rotation of the "labeled water." The study subjects drank a measured amount of water containing traceable isotopes of hydrogen and oxygen. Isotopes are atoms of a single element that have slightly different atomic weights, making them distinguishable from other atoms of the same element in a sample.
“If you measure the rate at which a person eliminates those stable isotopes through urine over the course of a week, the hydrogen isotope can tell you how much water they are replacing and the elimination of the oxygen isotope can tell us how many calories they consume. they’re burning,” says Schoeller, whose UW-Madison lab in the 1980s was the first to apply the labeled water method to study people.
More than 90 researchers participated in the study, which was led by a group that includes Yosuke Yamada, a former UW–Madison postdoctoral researcher in Schoeller’s lab and now section chief at the National Institute for Biomedical Innovation, Health and Nutrition in Japan, and John Speakman, professor of zoology at the University of Aberdeen in Scotland. They collected and analyzed data from the participants, comparing environmental factors, such as temperature, humidity, and altitude of the participants’ hometowns, to measure water renewal, energy expenditure, body mass, sex, age and status of the athlete.
The researchers also incorporated the United Nations Human Development Index, a composite measure of a country that combines life expectancy, schooling and economic factors.
The volume of water exchange peaked for men in the study during their 20s, while women maintained a plateau between 20 and 55 years of age. Newborns, however, removed the largest proportion daily, replacing about 28 percent of the water in their bodies every day.
Physical activity level and athletic status explained the largest proportion of the differences in water exchange, followed by sex, Human Development Index, and age.
All things being equal, men and women differ by about half a liter of water volume. As a sort of baseline, the study findings expect a non-athlete (but average physical activity) man who is 20 years old, weighs 70 kg (154 lb), to live at sea level in a country well developed in a medium air. temperature of 10 degrees C (50 Fahrenheit) and a relative humidity of 50%, you would take in and lose about 3.2 liters of water per day. A woman of the same age and activity level, weighing 60 kg (132 pounds) and living in the same location, would use 2.7 liters (91 ounces).
Doubling the energy a person uses will increase their expected daily water production by about a liter, the researchers found. Fifty more kilograms of body weight adds 0.7 liters per day. A 50% increase in humidity increases water consumption by 0.3 liters. Athletes use about a liter more than non-athletes.
The researchers found that "hunter-gatherers, mixed farmers, and subsistence farmers" had higher water turnover than people living in industrialized economies. In total, the lower the Human Development Index of your home country, the more water you will pass through in a day.
“That represents a combination of several factors,” Schoeller says. “Those people in countries with a low HDI are more likely to live in areas with higher average temperatures, more likely to do physical work, and less likely to be inside a climate-controlled building during the day. That, plus being less likely to have access to a sip of clean water when they need it, makes for a higher water turnover.”
The measurements will improve our ability to predict more specific and accurate future water needs, especially under extreme circumstances, according to Schoeller.
“Look at what’s happening in Florida right now, or in Mississippi, where entire regions have been exposed by a water shortage calamity,” he says. “The better we understand how much they need, the better prepared we will be to respond in an emergency.”
And we can better prepare for long-term needs and even notice short-term health problems, researchers believe.
“Determining the amount of water humans consume is increasingly important due to population growth and increasing climate change,” Yamada says. “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 of metabolic health.”
The study and access to the data were funded by agencies around the world, including the International Atomic Energy Agency, the National Science Foundation and National Institutes of Health of the United States, and the Chinese Academy of Sciences.
