Water turnover among human populations: Effects of environment and lifestyle

Abstract

Objectives: To discuss the environmental and lifestyle determinants of water balance in humans and identify the gaps in current research regarding water use across populations. Methods: We investigated intraspecific variation in water turnover by comparing data derived from a large number of human populations measured using either dietary survey or isotope tracking. We also used published data from a broad sample of mammalian species to identify the interspecific relationship between body mass and water turnover. Results: Water facilitates nearly all physiological tasks and water turnover is strongly related to body size among mammals (r2=0.90). Within humans, however, the effect of body size is small. Instead, water intake and turnover vary with lifestyle and environmental conditions. Notably, despite living physically active lives in conditions that should increase water demands, the available measures of water intake and turnover among small-scale farming and pastoralist communities are broadly similar to those in less active, industrialized populations.Conclusions: More work is required to better understand the environmental, behavioral, and cultural determinants of water turnover in humans living across a variety of ecosystems and lifestyles. The results of such work are made more vital by the climate crisis, which threatens the water security of millions around the globe.

Contribution of Dietary Composition on Water Turnover Rates in Active and Sedentary Men

“…Therefore, accurate assessment of body water turnover can be particularly useful in predicting (and hence, managing) fluid loss in individuals to prevent potential physical [ 2 ], physiological [ 3 , 4 ] and cognitive [ 5 ] declines associated with hypohydration [ 6 ]. The balance of body water, or fluid, is the difference between total fluid gain (influx) and loss (efflux) [ 1 , 7 ]. The majority of the fluid influx in humans is a result of the food and drink consumed, with a minor contribution from water absorbed by the skin or inspired through breathing [ 8 ].…”

“…The majority of the fluid influx in humans is a result of the food and drink consumed, with a minor contribution from water absorbed by the skin or inspired through breathing [ 8 ]. Most of the fluid efflux occurs via urine and ‘insensible’ water loss (i.e., exhaled water vapour, or water lost via the skin, but in the absence of sweating) [ 1 , 7 ]. Minor fluid efflux occurs via human faecal matter [ 7 ].…”

“…Most of the fluid efflux occurs via urine and ‘insensible’ water loss (i.e., exhaled water vapour, or water lost via the skin, but in the absence of sweating) [ 1 , 7 ]. Minor fluid efflux occurs via human faecal matter [ 7 ]. Sweat production can also significantly contribute to an individual’s fluid efflux either in times of heightened physical activity and/or in hot climates [ 9 ].…”

Water & Human Biology and New Developments for the American Journal of Human Biology

“…The volume opens with an introductory overview by Rosinger and Brewis (), and is followed by Amber Wutich's () Pearl Lecture that identifies water insecurity as a critically important research domain for human biologists. The papers by Swanson and Pontzer () and Rosinger () examine the physiology of hydration and water turnover. These papers underscore how much is still unknown about variation human water needs, and outline important directions for future research.…”

Life and death: Toward a human biology of water

“…For example, do the recommendations of 50 L a day per person (Gleick, ) as a basic minimum amount for all water needs make biocultural sense? We open with Swanson and Pontzer's (, this issue) review which examines a key aspect of human water needs—those of water turnover physiology, or the amount of water used on a daily basis. In their review, they demonstrate that water turnover across Western and small‐scale populations is driven largely by environmental and lifestyle differences.…”