Study debunks myth of 2 liters of water per day – DW – 12/02/2022

Is this the end of counting glasses of water? According to a group of more than 90 researchers, human beings do not necessarily need to drink eight glasses of water (approximately two liters) a day.

A large study recently released by the journal science guarantees that the daily consumption of liquid is determined by several individual factors, such as age, gender and physical condition, and external factors, such as relative humidity, temperature and even the Human Development Index (HDI) of the region.

Figure of person drinking water from a bottle against light, with the sun in the background
Farmer drinks water during heat wave in India: one in three people in the world do not have access to clean waterPhoto: Nitin Kanotra/Xinhua News Agency/picture alliance

The survey was conducted with more than 5,600 people from 23 countries, aged between 8 days and 96 years and with an average daily water consumption of 1 to 6 liters.

The participants were given 100 ml of “double-labeled water”, that is, they ingested 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 of elimination of these stable isotopes through the urine over the course of a week, the hydrogen isotope can reveal how much water is being replaced, and the oxygen isotope elimination shows how many calories are being burned,” he explains. Dale Schoeller, co-author of the study.

There is no “one size fits all”

Despite the fact that water is essential for survival, one in three people around the world do not have access to clean drinking water.

After reviewing the results, the scientists concluded that there are several variables when it comes to optimal daily water intake.

“The current study does not clearly indicate that there is a single guideline regarding the amount of drinking water to be consumed. And the popular suggestion that we should drink eight glasses of water a day is not supported by objective evidence”, explain the researchers. .

They compared environmental factors such as temperature, humidity and altitude of the hometowns to measured water volume, energy expenditure, body mass, sex, age and physical fitness.

The volume of water turnover peaked for men around age 20, while women maintained a plateau from age 20 to age 55. Newborns, on the other hand, had the highest daily proportion, replacing about 28% of body water every day.

Under exactly the same conditions, men and women differ by about half a liter of water. A 20-year-old male athlete who weighs 70 kg and lives near the sea with a relative humidity of 50% and a temperature of 10°C, has a turnover of about 3.2 liters of water per day.

A non-athlete woman of the same age and living under the same conditions will have a turnover of about 2.7 liters per day.

Physical condition and environmental factors also count

Levels of physical activity and fitness explained the greatest proportion of differences in water turnover, followed by gender, Human Development Index and age.

“It’s a combination of several factors,” says Schoeller. “People in low HDI countries are more likely to live in areas with higher average temperatures and to do manual labor, and less likely to be inside a climate-controlled building during the day. These factors, in addition to being less likely to have access to drinking water whenever you need it, increase the turnover of water.”

Why does water have no color, smell or taste?

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In general terms, the researchers concluded that the lower the Human Development Index of the country of origin, the greater the turnover of water in the body.

“Determining the amount of water consumed by humans is increasingly important due to population growth and climate change,” explains Yosuke Yamada, one of the study’s researchers. “Because water turnover is related to other important health indicators such as physical activity and body fat percentage, it has the potential to be a biomarker for metabolic health.”

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