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Abstract:
Water is essential for survival, but one in three individuals worldwide (2.2 billion people) lacks access to safe drinking water. Water intake requirements largely reflect water turnover (WT), the water used by the body each day. We investigated the determinants of human WT in 5604 people from the ages of 8 days to 96 years from 23 countries using isotope-tracking (2H) methods. Age, body size, and composition were significantly associated with WT, as were physical activity, athletic status, pregnancy, socioeconomic status, and environmental characteristics (latitude, altitude, air temperature, and humidity). People who lived in countries with a low human development index (HDI) had higher WT than people in high-HDI countries. On the basis of this extensive dataset, we provide equations to predict human WT in relation to anthropometric, economic, and environmental factors.
Water is essential for life (1), and daily water intake is necessary to prevent dehydration (i.e., net loss of body water) in most terrestrial animals, including humans (2). Total body water (TBW, measured in liters) is homeostatically controlled (3) and tightly regulated day to day by thirst and hunger drives that lead to the intake of fluids and food to offset water losses (4). Body water is lost as urine, insensible transcutaneous evaporation and sweat loss, respiratory water vapor, and water in feces (Fig. 1A). To maintain water balance, these losses must be matched by intake of water from liquids (drinking water and other beverages) and foods (5, 6), water vapor in respiratory air intake, transcutaneous water uptake, and water formed during aerobic respiration and metabolism (Fig. 1A) (2, 7). The total movement of water through the body, both intake and loss, is called water turnover (WT, measured in liters per day).
