Water Intake, Water Balance, and the Elusive Daily Water Requirement

Abstract

Water is essential for metabolism, substrate transport across membranes, cellular homeostasis, temperature regulation, and circulatory function. Although nutritional and physiological research teams and professional organizations have described the daily total water intakes (TWI, L/24h) and Adequate Intakes (AI) of children, women, and men, there is no widespread consensus regarding the human water requirements of different demographic groups. These requirements remain undefined because of the dynamic complexity inherent in the human water regulatory network, which involves the central nervous system and several organ systems, as well as large inter-individual differences. The present review analyzes published evidence that is relevant to these issues and presents a novel approach to assessing the daily water requirements of individuals in all sex and life-stage groups, as an alternative to AI values based on survey data. This empirical method focuses on the intensity of a specific neuroendocrine response (e.g., plasma arginine vasopressin (AVP) concentration) employed by the brain to regulate total body water volume and concentration. We consider this autonomically-controlled neuroendocrine response to be an inherent hydration biomarker and one means by which the brain maintains good health and optimal function. We also propose that this individualized method defines the elusive state of euhydration (i.e., water balance) and distinguishes it from hypohydration. Using plasma AVP concentration to analyze multiple published data sets that included both men and women, we determined that a mild neuroendocrine defense of body water commences when TWI is ˂1.8 L/24h, that 19–71% of adults in various countries consume less than this TWI each day, and consuming less than the 24-h water AI may influence the risk of dysfunctional metabolism and chronic diseases.

A 10‐year study of the etiopathogenesis of cysts with a study of seromucinous glands in vocal folds

“…They found better voice quality after adequate surface hydration. 16 Adequate hydration of the body is considered to be 2 liters or eight glasses of water 17,18 and agents that dehydrate the body result in decreased laryngeal hydration and thick secretions, which may block the ductal system of seromucinous glands with a resultant formation of a mucous retention cyst. We considered laryngeal hydration to be poor when a person consumed less than or equal to four glasses of water a day or consumed more than 8 caffeinated beverages (tea/coffee/cola) in a day.…”

Measuring Human Water Needs

“…These biomarkers stabilize within 24 hours to reflect the current water intake state. The mechanism behind changes in urine concentration and urine volume are due to changes in vasopressin, or anti‐diuretic hormone vasopressin, secretion which is released in response to body water excesses or deficits (Armstrong & Johnson, ). Biomarkers of urine concentration respond acutely to changes in water intake, unlike plasma osmolality, which is less responsive to acute changes in water intake (Cheuvront et al, ; Perrier et al, ).…”

“…Like other ELISA kits, it necessitates a full wet lab with microplate readers, an incubator, microtiter plate, graduated cylinders, distilled water, pipettes, and test tubes. While vasopressin is a newer biomarker of hydration, it is well correlated with urinary biomarkers of hydration and parlays into the neural circuitry designed to keep body water homeostasis (Armstrong & Johnson, ). However, vasopressin can be quite unstable in lab analyses, attaches to platelets and is cleared rapidly (Morgenthaler, Struck, Alonso, & Bergmann, ).…”

Biobehavioral variation in human water needs: How adaptations, early life environments, and the life course affect body water homeostasis

“…However, a recent randomized control study among those who already had stage 3 CKD found that those who received coaching to drink more water (an extra liter a day) did not have significantly slower declines in kidney function (Clark et al, ). Therefore, daily water intake among those without kidney damage likely provides the most benefits to kidney health (Armstrong & Johnson, ; Clark et al, ).…”

“…Since water balance is intimately tied to health and physiological functioning, several systems exist, including thirst, to return the body to homeostasis (Oka, Ye, & Zuker, ). The body and brain detect water deficits and excesses thereby releasing or restricting the anti‐diuretic hormone vasopressin and conserving body water or excreting it with the signals getting stronger depending on the level of imbalance (Armstrong & Johnson, ).…”