The recommendation to drink at least eight glasses of water a day “is probably excessive” for most people, according to scientists, writes the Guardian. However, the suggestion has now become almost common practice, so much so that it has been included in the “Guide to Optimal Health Status.” But this is not the case.

The latest study, far more rigorous than those done so far on water replacement, reveals that people have “a wide range of needs” on drinking water: many need only 1.5 to 1.8 liters a day, less than the recommended two liters, the research suggests.

But there is also an aspect in itself that is paradoxical, because “the current recommendation is not scientifically supported at all,” said Yosuke Yamada of the National Institute of Biomedical Innovation, Health and Nutrition in Japan, one of the study’s most credentialed authors, to the point that in his view “most scientists are not sure where this recommendation comes from.” In short, counter-argument, the recommended eight glasses of water a day are no longer necessary.

The study states that previous estimates of individual water needs “tended to ignore the water content of food, which can contribute a substantial part of our overall intake.”

That is, “if you eat only bread, bacon and eggs you won’t get much water from what you eat, but if you eat meat, vegetables, fish, pasta and rice you can get about 50 percent of your water needs just from food,” Yamada said.

The research published in Science evaluated the water intake of 5,604 people aged eight days to 96 years from 23 countries and involved people drinking a glass of water in which some of the hydrogen molecules were replaced by a stable isotope of the element deuterium, which occurs naturally in the human body and is harmless.

The rate of elimination of extra deuterium reveals how quickly water in the body is transformed, and the study found that the extent varies widely depending on a person’s age, sex, activity levels and surroundings. Those who live in hot and humid climates and at high altitudes as well as athletes and pregnant and nursing women have higher turnover, which means they need to drink more water.

Moral. “Energy expenditure is the most important factor in water turnover, with the highest values observed in men aged 20-35 years, averaging 4.2 liters per day. This decreased with age, with an average of 2.5 liters per day for men aged 90 years. Women in their 20s and 40s had an average requirement of 3.3 liters, which dropped to 2.5 liters at age 90. Athletes require about one liter more than non-athletes. Infants turned the largest percentage, replacing about 28 percent of the water in their bodies each day,” the Guardian reports.

Scientific-technical conclusion: “If 40 million adults in the UK followed the guidelines and drank half a liter more water than they needed each day, that would be 20 million liters of water wasted each day,” the researchers say.

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