Hydration biomarkers in free-living adults with different levels of habitual fluid consumption

Abstract

Little is known about the impact of habitual fluid intake on physiology. Specifically, biomarkers of hydration status and body water regulation have not been adequately explored in adults who consume different fluid volumes in everyday conditions, without prolonged exercise or environmental exposure. The purpose of the present study was to compare adults with habitually different fluid intakes with respect to biomarkers implicated in the assessment of hydration status, the regulation of total body water and the risk of kidney pathologies. In the present cross-sectional study, seventy-one adults (thirty-two men, thirty-nine women, age 25–40 years) were classified according to daily fluid intake: thirty-nine low drinkers (LD; ≤ 1·2 litres/d) and thirty-two high drinkers (HD; 2–4 litres/d). During four consecutive days, urinary parameters (first morning urine (FMU) on day 1 and subsequent 24 h urine (24hU) collections), blood parameters, and food and beverage intake were assessed. ANOVA and non-parametric comparisons revealed significant differences between the LD and HD groups in 24hU volume (1·0 (se 0·1) v. 2·4 (se 0·1) litres), specific gravity (median 1·023 v. 1·010), osmolality (767 (se 27) v. 371 (se 33) mOsm/kg) and colour (3·1 (se 0·2) v. 1·8 (se 0·2)). Similarly, in the FMU, the LD group produced a smaller amount of more concentrated urine. Plasma cortisol, creatinine and arginine vasopressin concentrations were significantly higher among the LD. Plasma osmolality was similar between the groups, suggesting physiological adaptations to preserve plasma osmolality despite low fluid intake. The long-term impact of adaptations to preserve plasma osmolality must be examined, particularly in the context of renal health.

Two Liters a Day Keep the Doctor Away? Considerations on the Pathophysiology of Suboptimal Fluid Intake in the Common Population

“…Total water intake (sum of water from food moisture and fluids) varies considerably in the common population [8, 9]. The impact of low daily water intake on long term health has, in the past, attracted little attention [10].…”

“…A recent study revealed, however, that plasma vasopressin (ADH) levels were significantly enhanced in low drinkers (≤ 1.2 litres/d of total fluid intake, i.e. sum of drinking water and any other fluids) as compared to high drinkers (2–4 litres/d) [8, 11]. Vasopressin is a known powerful stimulator of glucocorticoid release [4, 5] and low drinkers had indeed significantly higher plasma cortisol levels [8].…”

“…sum of drinking water and any other fluids) as compared to high drinkers (2–4 litres/d) [8, 11]. Vasopressin is a known powerful stimulator of glucocorticoid release [4, 5] and low drinkers had indeed significantly higher plasma cortisol levels [8]. The pleotropic effects of glucocorticoids include upregulation of the s erum- and g lucocorticoid-inducible k inase 1 (SGK1) [6, 7, 12], an ubiquitously expressed kinase up-regulated during dehydration [13, 14].…”

Prevalence of Inadequate Hydration Among US Children and Disparities by Gender and Race/Ethnicity: National Health and Nutrition Examination Survey, 2009–2012

“…Additionally, although a review of international studies found significant differences in hydration status by age, gender, race/ethnicity, and culture, 11 there is limited evidence about the population distribution of urine osmolality and inadequate hydration among US children, particularly whether disparities in hydration status exist across population groups defined by race/ethnicity, household income, gender, or age. Although small, laboratory-based studies of adults suggest that higher beverage intake is associated with better hydration status (regardless of beverage type), 12,13 preliminary evidence has suggested that plain water may be associated with better hydration status in children. 10 Given that little is known about how consumption of different beverages may affect population hydration status in children, the potential solutions to reducing inadequate hydration are unclear.…”

Fluid Intake and Vasopressin: Connecting the Dots

“…Moreover, individuals with habitually lower fluid intake have higher circulating AVP, lower 24-hour urine volume and higher urine concentration [10,11] . Given that higher circulating AVP is an indicator of chronic or habitual antidiuresis (indicating insufficient water intake), these findings suggest that there may be biologically significant interconnections between AVP, water intake and renal and metabolic health ( fig.…”