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Eight daily glasses of water ‘excessive’, study suggests

Posted on the 8th December 2022

Water Study

Scientists believe the ‘one size fits all’ guidance could also lead to millions of litres of drinking water being wasted daily.

The suggestion that two litres of water are a daily necessity has become accepted wisdom and often appears in health guidance.

However, this latest work, the most rigorous study to date on water turnover, has revealed that people have a wide range of water intake needs and many only require about 1.5 to 1.8 litres a day.

The study, published in the journal Science, assessed the water intake of 5,604 people aged between eight days and 96 years old from 23 countries. The research involved people drinking a glass of water in which some of the hydrogen atoms were replaced by deuterium, a stable isotope of hydrogen that is found naturally in the human body and is harmless.

The rate of elimination of the extra deuterium reveals how quickly the water in the body is turned over, and the study found the measure varied widely depending on a person’s age, gender, activity levels and surrounding.

Those living in hot and humid climates and at high altitudes, as well as athletes and pregnant and breastfeeding women, had a higher turnover, meaning they need to drink more water.

Energy expenditure is the biggest factor in water turnover, with the highest values observed in men aged 20 to 35, with an average of 4.2 litres a day.

This decreased with age, averaging 2.5 litres a day for men in their 90s. Women aged 20 to 40 had an average turnover of 3.3 litres, which declined to 2.5 litres by the age of 90.

Athletes turn over around a litre more than non-athletes. Newborn babies turned over the largest proportion, replacing about 28 per cent of the water in their bodies every day.

While we often hear about the importance of consuming eight glasses of water daily, the source of the recommendation remains unknown.

“The current recommendation is not supported scientifically at all,” said Yosuke Yamada of the National Institute of Biomedical Innovation, Health and Nutrition in Japan, and one of the paper’s first authors. “Most of the scientists are not sure where this recommendation came from.”

Despite this, water intake is essential for maintaining the proper function of all organs and tissues in the human body – many of us just don’t need as much of it as we originally thought.

Related: Water linked to heart health

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