Overturn the recommendation of 8 glasses of water a day! Scientists reveal the law of human water demand

Expert interviewed: Yu Renwen, director of Beijing Nutritionist Association

Global Times health client End reporter Yu Ye

Water is the basic substance to maintain the metabolism of living organisms, accounting for about 60%-70% of the body weight. A lot of health information often circulates a saying – you must drink eight glasses of water a day to be good for your health. Is this statement scientific? On November 24, the team of John Roger Spicman, Chief Scientist of the Energy Metabolism and Reproduction Research Center of the Institute of Medicine, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, and Chair Professor of the School of Pharmacy, Shenzhen University of Technology (preparation), joined forces with Kyoto University of Advanced Science and Technology Nearly 100 international research teams from research institutions such as University of Roehampton in the United Kingdom, University of Tsukuba in Japan, and Duke University in the United States published research papers in the journal Science, deriving the world’s first formula for predicting the daily water demand of the human body, revealing for the first time The law of water demand throughout the human life cycle shows that the recommendation of 8 glasses of water (about 2 liters) per day is not supported by scientific evidence.

This study used the stable isotope method (tritium) for A total of 5,604 subjects (3,729 women, 1,875 men) from 23 countries were studied, and the sample size ranged from 8-day-old infants to 96-year-olds. Objective, accurate, reliable and precise measurements of their total water (TBW) and water turnover (WT) under different living conditions were obtained. Total water (TBW), the total amount of water contained in the body, is controlled by homeostasis and is tightly regulated daily by thirst and hunger drives, with water and food intake compensating for body water loss. Water loss is mainly in the form of urine, sweat, skin evaporation, breathing and feces. To maintain water balance in the body, these losses must be matched by water intake from fluids (drinking water and other beverages) and food. The daily water turnover (WT) of the human body is the total exchange of water, including the water intake and water loss of the human body, and largely reflects our daily water demand.

Human water intake and loss

Research shows that people living in hot, humid environments and at high altitudes , as well as athletes, pregnant women, breastfeeding women and people engaged in heavy physical labor, the water turnover is higher. By age, water turnover was highest in men aged 20–30 years and in women aged 20–60 years, and total water (TBW) demand was highest in adults aged 20–60 years, after which it declined with age.

It is worth noting that water turnover is not equal to drinking water demand, such as the daily water turnover of a man in his 20s It is 4.2 liters, but there is no need to drink 4.2 liters of water, because human body metabolism and body surface water exchange can provide 15% of it, and the remaining 85% of the water demand comes from food and drinking water, and food and drinking water are divided in half, so this age group The average daily water intake for men is 1.5-1.8 liters. In contrast, women drink less water because their non-fat composition is lower than that of men. A woman in her 20s may drink 1.3-1.4 liters of water per day. The study also found that there are large individual differences in water turnover, and the water needs of people of different countries, different age groups, and genders are different. Therefore, the recommended amount of 8 glasses of water (about 2 liters per day) may be too high for most people. This kind of “one size fits all” health advice is not suitable for precise health guidance for individuals.

How much water should I drink every day and when should I drink it? Yu Renwen, director of the Beijing Nutritionist Association, told the reporter of the Global Times Health Client that the Dietary Guidelines for Chinese Residents (2022) recommends that adult women with light physical activity should have an appropriate daily total water intake (including water in food) The recommended daily total water intake (including water in food) for men with light physical activity is 3000 ml, and it is recommended to drink 1700 ml of water per day. People with light physical activity are equivalent to working in an office or without a large amount of exercise and without excessive sweating. It is recommended that the elderly drink about 1500 ml of water per day. How to judge whether the body is dehydrated mainly from three aspects:

1. Thirst: Thirst is a signal that the body is obviously dehydrated . Therefore, to avoid thirst, you should take the initiative to drink water.

2. Frequency and volume of urination: Generally, healthy adults urinate 4-8 times a day, and the daily urination volume is 500-4000 ml , about 300ml per urination,Frequency and volume of urination are closely related to water intake. When the body urinates less frequently and the amount of urine than usual, it indicates that the water intake is too low, and the body may appear dehydrated.

3. Urine color: The normal urine color of healthy adults is slightly yellow and transparent. When the water intake is sufficient, the normal urine color is transparent yellow or light yellow; when it appears darker yellow or dark yellow, it indicates that the body is insufficient or lacks water, and is in a state of dehydration.

How to drink water? Yu Renwen suggested that adults drink 1 cup of water each time, about 200 ml per cup, and the amount of water consumed by the elderly should be reduced appropriately. You can drink 1 glass of water in the morning and evening, and drink a glass of water every 1 to 2 hours at other times. Drinking large amounts of water at one time may increase the risk of water intoxication. It is recommended that the suitable temperature of drinking water be between 10°C and 40°C. It is recommended to drink boiled water or tea, and drink as little or no sugary drinks as possible. Beverages cannot replace plain water. In addition, for patients suffering from heart disease, high blood pressure, kidney disease and edema, drinking too much water will increase the burden on the heart and kidneys. Such patients should drink water in moderation, and the amount of drinking water should follow the doctor’s advice. However, bodybuilders who exercise a lot, people who sweat excessively in hot weather, heavy physical laborers, patients with urinary stones or inflammation, and patients with gout and hyperuricemia can appropriately increase their drinking water to help excrete uric acid , relieve inflammation.

Source: “Life Times”