The commonly held belief that eight 8-ounce glasses of water per day are sufficient to cover a person’s daily needs has been disproved by a recent study involving thousands of participants. The results show that people’s water drinking needs varies widely around the globe and across their lifetimes.
According to Dale Schoeller, a longtime researcher of water and metabolism at the University of Wisconsin-Madison, “the science has never supported the old “eight glasses” thing as an appropriate guideline, if only because it confused total water turnover with water from beverages, and a lot of your water comes from the food you eat.” “However,” the authors write, “our work is the best we’ve done thus far to estimate how much water people actually eat on a daily basis—the turnover of water into and out of the body—and the primary elements that drive water turnover.”
That is not to claim that the new findings establish a new standard. More than 5,600 individuals from 26 nations, ranging in age from 8 days to 96 years old, had their water turnover assessed for the study, which was published today in the journal Science. The results showed that the average water turnover ranged from 1 to 6 liters on a daily basis.
According to Schoeller, a co-author of the study, “there are outliers, too, that are turning over as much as 10 liters a day.” “Because of the variety, focusing on one average isn’t very informative.” “The database we’ve created reveals the significant factors that differing water turnover correlates with.”
Previous water turnover research relied primarily on volunteers recalling and self-reporting their water and food consumption, or it was based on focused observations, such as a small group of young, male soldiers working outside in the desert, of dubious use as representative of most people.
By monitoring the turnover of “tagged water,” the new study was able to measure how long it took for water to pass through the bodies of study participants. A predetermined amount of water with traceable hydrogen and oxygen isotopes was consumed by study participants. Isotopes are atoms of a single element that can be distinguished from other atoms of the same element in a sample by having slightly differing atomic weights.
According to Schoeller, whose UW-Madison lab was the first to use the labeled-water method to study people in the 1980s, if you monitor a person’s rate of eliminating those stable isotopes through their urine over the course of a week, the hydrogen isotope can tell you how much water they’re replacing, and the elimination of the oxygen isotope can tell us how many calories they’re burning.
The study, which included more than 90 researchers, was led by a team that included John Speakman, a 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 section head of the National Institute of Biomedical Innovation, Health, and Nutrition in Japan. Participants’ ambient characteristics, such as hometown temperature, humidity, and altitude, were compared to measurements of water turnover, energy expenditure, body mass, sex, age, and athletic status.
The researchers also took into account the Human Development Index (HDI), a composite indicator of a nation that incorporates economic, educational, and life expectancy data.
In the study, men’s water drinking needs turnover volume peaked in their 20s, whereas women’s water turnover volume plateaued from 20 to 55 years of age. However, newborns had the highest rate of daily water replacement, restoring nearly 28% of their body weight each day.
Following sex, the Human Development Index, and age, physical activity level and athletic status accounted for the biggest percentage of the variations in water turnover.
Men and women have a roughly 0.5 liter difference in water turnover, all other variables being equal. According to the study’s findings, a 20-year-old male who is not an athlete but engages in average physical activity weighs 70 kg (154 pounds), lives at sea level in a developed nation with a mean air temperature of 10 degrees Celsius (50 degrees Fahrenheit), a relative humidity of 50%, and experiences daily water intake and loss of about 3.2 liters. A lady of the same age, activity level, weight, and location would require 2.7 liters of water per day (91 ounces).
The researchers discovered that an individual’s projected daily water turnover will increase by around a liter if their energy use is doubled. 0.7 liters are added per kilogram of body weight every day. Water use increases by 0.3 liters for every 50% rise in humidity. A liter or so more is used by athletes than by non-athletes.
Hunter-gatherers, mixed farmers, and subsistence agriculturalists all had higher water turnover than residents of industrialized economies, according to the researchers. Overall, the less developed your home country is, the more water drinking needs you use each day.
According to Schoeller, “that’s representing the synthesis of various components.” “People who reside in low HDI nations are more likely to do physical labor, live in regions with higher average temperatures, and spend less time indoors in climate-controlled environments during the day.” “Their water turnover is larger as a result of this and the decreased likelihood that they would always have access to a drink of clean water.”
According to Schoeller, the measures will increase our capacity to forecast future water drinking needs with greater specificity and accuracy, particularly under emergency conditions.
Look at what’s happening in Florida or Mississippi right now, he says, where disasters have made entire regions vulnerable to water shortages. “The better equipped we are to respond in an emergency, the more we understand how much they require.”
The researchers believe that the better we can anticipate long-term demands, the more we may even be aware of immediate health issues.
A growing population and a changing environment make it more crucial than ever to know how much water people use, according to Yamada. Water turnover has the potential to serve as a biomarker for metabolic health because it is related to other significant health indicators, such as physical activity and body fat percentage.
The International Atomic Energy Agency, the National Science Foundation, the National Institutes of Health in the United States, and the Chinese Academy of Sciences all provided funding for the study and access to the data.
