A new global study of human water requirements by Yosuke Yamada and colleagues shows how water turnover – the water used by the body daily – differs and is determined by a variety of factors in people across the globe. Although data on water consumption and turnover are critical to global health decision-making and planning for future water needs, some recommendations for human water intake rely on self-reported data, which can be variable. Yamada et al. measured water turnover and total body water for 5,604 people, ages 8 days to 96 years, from 26 countries around the globe. Their method asks participants to drink a small amount of deuterium-enriched water, tracing the loss of deuterium to assess water turnover and its dilution to estimate total body water. The researchers confirmed that body size and composition, climate variables, pregnancy, and energy expenditure were all correlated with water turnover. People in countries with a low human development index (a measure of education, income, and life expectancy) had higher water turnover than those with a middle or high index, even when accounting for other environmental and physiological variables, they found. Turnover was greatest in 20- to 30-year-old men and 20- to 55-year-old women, and total body water was highest in adults 20 to 40 years old. Based on these data, the researchers also developed an equation that can be used to predict water usage for an individual.
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