Water is necessary for survival, but one in three people worldwide does not have access to clean drinking water. Water consumption requirements are usually based on daily water use by the body or water turnover (WT). However, it is a challenge to objectively assess the water requirement. Most previous research was based on subjective surveys given to relatively few individuals.
A new study by Prof. John Speakman of the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences (CAS) and the University of Aberdeen examined the determinants of human water turnover in 5604 people aged eight days to 96 year from 23 countries. They used an isotope labeling technique to track water intake and loss in individuals.
Their study shows that the recommended intake of eight 8 oz glasses of water per day (about 2 L/day) is too high for our actual needs in many situations. Water turnover was higher in hot and humid environments and at high altitudes in athletes, pregnant and lactating women, and individuals with high levels of physical activity.
However, energy consumption has the greatest impact on water turnover. Because this group had the highest energy expenditure, the highest values were seen in men between the ages of 20 and 35. Their daily water turnover averaged 4.2 L. As people aged, this amount decreased, with men in their 90s consuming an average of only 2.5 L per day. Between the ages of 20 and 40, the average water turnover of women was 3.3 l/day; by 90 it had fallen to about 2.5 l/d.
In addition, water turnover was higher in developing countries. This is likely due to the fact that the air conditioning and heating systems of developed countries protect people from extreme environmental conditions that increase the demand for water.
prof. speakman said: “It should be noted that water turnover does not equate to drinking water needs. Even if a man in his twenties has an average water turnover of 4.2 l/day, he still does not need to drink 4.2 l of water per day. About 15% of this value reflects the exchange of surface water and water produced by metabolism. The required water intake is therefore about 3.6 l/day.”
“Because most foods also contain water, you get a substantial part through eating. But because the water content of foodstuffs varies so much, it is difficult to determine the exact drinking water requirement.”
“For a typical man in his 20s in the US or Europe, more than half of the 3.6 liters of water needed each day probably comes from food, meaning the amount to be consumed through drinking is about 1. 5–1.8 liters per day. . For a woman in her 20s, that is probably about 1.3 to 1.4 liters per day.”
“Older people will generally need less while living in a warm climate. More physical activity and being pregnant or breastfeeding will increase this figure.”
prof. ZHANG Xueying of SIAT, co-first author of the study, said: “It is important to find out how much water people need because of the explosive population growth and increasing climate change. Water turnover is related to many health parameters such as physical activity, body fat percentage, etc., making it a new potential biomarker for metabolic health.”
- Yosuke Yamada, Xueying Zhang et al. Variation in human water turnover associated with environmental and lifestyle factors. Science. DOI: 10.1126/science.abm8668