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NCT07464002

Effects of Habitual Water Intake on Thirst in Healthy Young Adults Explained by Osmoadaptive Metabolism, Brain and Kidney Function (Adapt-Thirst)

Sponsor: Jodi Stookey

View on ClinicalTrials.gov

Summary

Social relevance: For 30 years, people have been confused about how much plain water to drink. Over 30 years, health professionals have criticized media advice to drink 8 glasses of water per day, citing lack of evidence (Valtin et al, 2002; Yamada et al, 2022). Health authorities have not set drinking water-specific recommendations, assuming 1) that any or all types of drinks hydrate equivalently, i.e. that people do not need to drink plain water to replace lost body water, and 2) the average healthy person can rely on thirst as guide for water intake. The lack of drinking water-specific recommendations significantly impacts daily lives because it translates into limited or no support for drinking water in public health services, laws, and retail options. Scientific relevance: Thirst is considered the primary driver of water intake and main defense against body water deficit in healthy young adults (IOM, 2005). Health authorities set total water intake recommendations for the average healthy man and woman (e.g. 2.5 L/d for men and 2.0 L/d for women in Europe) but, additionally, advise people to use thirst as a guide for water intake, recognizing that individual water requirements vary widely (EFSA, 2010; IOM, 2005). Although thirst can be satiated by water intake, it can also be ignored per custom (Greenleaf, 1992) or suppressed by an upward-shifted thirst threshold. The thirst threshold, the set-point where osmoreceptor cells shrink and release their neural or hormonal signal, is a function of the solute concentration or osmolality inside and outside the osmoreceptor cells (Nose et al, 1988a,b). Cells with higher intracellular solute content require a higher external osmolality to shrink. Specific Aims The ultimate goal of this study is to address gaps in the literature about drinking water and check assumptions that limit the development of drinking water-specific recommendations. The study will examine if osmoadaptation to chronic hypertonicity, due to daily intake of hypertonic fluid sources, can explain suppressed thirst in healthy individuals under conditions of daily life. To facilitate causal inference about drinking water effects for long-term health, this study was designed to link experimental data about osmoadaptation at the cellular level with clinical data relevant for conditions of daily life in Salzburg Austria with population-based data about water intake and chronic disease risk in Salzburg Austria. This study will test effects of drinking enough plain water to dilute urine everyday for 4 weeks (about 500 mL 4 times per day in summer). The study will include healthy, normal weight, young, men and women, who all usually meet European adequate intake recommendations for total water intake (TWI), but usually consume less than 1L/d PWI, and have biomarkers of chronic hypertonic stress (concentrated urine and saliva) for 4 consecutive weeks before starting the randomized study.

Official title: Studie Zum Habituellen Durst Und Adapt Durst Studie: Habitual Thirst Study and Adapt Thirst Study

Key Details

Gender

All

Age Range

19 Years - 29 Years

Study Type

INTERVENTIONAL

Enrollment

120

Start Date

2026-05-01

Completion Date

2027-12-31

Last Updated

2026-03-11

Healthy Volunteers

Conditions

Chronic Underhydration Thirst; Due to Deprivation of Water Aestivation Metabolism Warburg Effect Osmoadaptation Dysglycemia Protein Breakdown Brain Function Healthy

Interventions

OTHER

Drinking water to dilute urine

After Weeks 1-4 baseline data collection, people randomized in Week 5 will be instructed to increase drinking water to approx. 4 times 500 mL/d in Weeks 6-9 to reach a volume that is enough to dilute urine specific gravity below 1.013 everyday. The PWI exposure is approx. 20 mL/kg PWI for men, 25 mL/kg PWI for women. Addition of PWI to the diet may increase TWI and minimally displace some other beverage intake. Based on Adapt Study data, the hypo-osmotic share of TWI is expected to increase from below 50% to 50% or higher. The intervention dose is also aligned with observational data from the Paracelsus 10000 study in Salzburg, which found that healthy adults who met hydration criteria reported at least 1L/d PWI. The intervention will be communicated to participants in terms of L/d instead of mL/kg, because L/d are easier to translate into portion size and drinking behavior.

All randomized participants must have complete data from 4 weeks of screening. All inclusion criteria below must be met: * 4 weeks of 3-day mean total water intake of 35 ml/kg body weight * 4 weeks of \<1L/d drinking water * 4 weeks of \<1 hr/d moderate or vigorous physical activity given daily life conditions in Salzburg, Austria * No history of chronic disease * Normal blood pressure, * Normal blood chemistry and complete blood count (CBC) test results * Normal overnight urine concentration, and normal acute urine dilution after 500mL drinking water * Normal weight and height between 160-170 cm for women and 175-185 cm for men) * After overnight food and water restriction urine osmolality above 800 mmol/kg, salivary osmolality above 100 mmol/kg, and a thirst score below 70 mm on a 100 mm visual analog scale. Exclusion Criteria: * Individuals will be excluded from participation if the gender-specific target numbers have already been reached * Perceived stress score of \> 20 at any time during Weeks 1-4 * Schedule that does not allow continuous study participation * Intention to spend more than a day outside the Salzburg area during the study period (to reduce exposure to ground water with different background D2O as potential source of error) * Headache within the last six months * Pregnant, planning a pregnancy, or irregular or unknown menstrual cycle * Active use of tobacco or e-cigarettes * Daily consumption of alcohol * Regular use of medication * Agoraphobia or claustrophobia that would prevent brain fMRI testing * Metal-containing intrauterine device (IUD) that would prevent fMRI testing * Doubtful or unwilling to complete all study procedures (including drinking alcohol; drinking plain tap water, blood tests, 24-hour urine collection, fMRI scans, and stable isotope tests) * Unwilling to be randomly assigned to intervention or control * Incomplete baseline data in Weeks 1-4 (including blood tests, 24-hour urine collection, and MRI scans).