For the first time, scientists have revealed the law of water demand throughout the life cycle of human beings

Schematic diagram of water turnover Illustration courtesy of the research team

Is it really scientific to drink eight glasses of water (about 2 liters) a day for good health?

On November 25, a study published in Science concluded that unlike previous perceptions of drinking water, the above drinking water recommendations may exceed the true water needs of most people.

John Roger Speakman, chief scientist of the Energy Metabolism and Reproduction Research Center of the Institute of Biomedicine and Technology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, and chair professor of the School of Pharmacy of Shenzhen University of Technology, together with nearly 100 international teams, studied 5604 subjects in 26 countries based on the stable isotope method, with samples ranging from 8-day-old infants to 96-year-olds. The world’s first formula for predicting the daily water demand of the human body was derived, revealing for the first time the law of water demand throughout the life cycle of human beings.

“Understanding the factors that influence water turnover and the relative importance of each is a big step forward in projecting future water demand. This work builds on contributions from scientists from around the world and demonstrates the importance of international scientific collaboration in answering major scientific questions. Speakman said.

Water is the source of life. Without water, humans can only survive for three days. The daily water turnover of the human body (Water Turnover), which is the total exchange of water, including the water we ingest and the water we lose, largely reflects people’s water needs.

Based on the international “double standard water” database, the scientific research team measured the water turnover rate of the subjects using deuterium dilution technology, and found that the daily water turnover of men aged 20~35 was 4.2 liters, and the daily water turnover of women aged 30~60 was 3.3 liters, and then decreased with age, and fell to about 2.5 liters in their 90s.

For example, a man in his 20s has a daily water turnover of 4.2 liters, but does not need to drink 4.2 liters of water, because human metabolism and surface water exchange can provide 15% of it, and the remaining 85% of water demand comes from food and drinking water, food and drinking water are halved, so the average daily water intake of men in this age group is 1.5-1.8 liters. In contrast, women drink less water because women have a lower non-fat component than men, for example, a woman in her 20s may drink 1.3-1.4 liters of water per day.

“One of the main findings of the study is the recommended amount of 8 glasses of water (or about 2 litres per day) that we should all drink, but it is probably too high for most people.” Zhang Xueying, assistant researcher of Shenzhen Advanced Institute, said.

Studies have found that individual differences in water turnover are large, for example, in adults alone, some people have a daily water turnover rate of only 5% of their body water, while others have a water turnover rate of as high as 20%. People of different ages, genders, and countries have different water needs. Therefore, “one-size-fits-all” health advice is not suitable for precise health guidance for individuals.

Since the 80s of the 20th century, the “double standard water” method has explored the body’s energy metabolism by collecting the subject’s urine for 14 days and analyzing the changes in the abundance value of the markers, which is the “gold standard” for detecting the energy expenditure of the human body in the free living state.

Previous studies on human water demand have relied on subjective questionnaires and physiological studies in the laboratory, with small sample sizes and imprecise assessment methods. The research team used deuterium dilution technology to objectively and accurately measure the water turnover rate of the subjects, and explored the influence of factors such as weight, age, body composition, total energy expenditure, physical activity level, as well as climate, latitude, altitude, temperature and humidity on the water turnover rate throughout the human life process.

The analysis found that people living in hot and humid environments and high altitudes, as well as athletes, pregnant and lactating women, and people with high levels of physical activity, had higher water turnover; Water turnover is higher in developing countries and among people engaged in heavy physical work; Daily physical activity increases water turnover.

The study shows that water turnover rate has been shown to be related to more physiological health indicators, such as physical activity level and body fat rate, and at the same time, the concept that water turnover rate can be used as a new biomarker reflecting human metabolic health is proposed for the first time, which provides new ideas for the study of various metabolic chronic diseases such as obesity and diabetes.

Based on the influence of the above factors on water turnover, researchers developed the world’s first equation for predicting human water turnover. “This equation can be applied to countries and regions around the world, and only need to understand a person’s basic physiological indicators and the average temperature and humidity of the living environment to predict a person’s water demand.” Zhang Xueying introduced.

With the change of world population structure and climate warming, this study provides the equations used to predict human water demand under the guidance of large data sets, and provides an important scientific basis for the future development of drinking water and water-rich food management plan improvement.

“Water is necessary for life, water turnover is closely related to water demand, and this study has taken the first step to build a personalized predictive water turnover algorithm.” Speakman said. At present, the Shenzhen Advanced Institute where Speakman is located has established the first “double standard water” laboratory and precision human nutrition laboratory in China, which will further reveal the law of life and provide scientific guidance for human beings to formulate precision nutrition strategies.

This is the second important result published in Science after Speakman and the international team first revealed the laws of human life cycle metabolism in Science in 2021. (Source: Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences)

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