Water supplementation after dehydration improves judgment and decision-making performance

Origins of thirstiness sensation and current food solutions

The sensation of thirstiness is the desire to drink water. In certain situations, the ingestion of liquid water can be restricted. As a result, thirstiness is not relieved, resulting in an uncomfortable and distressing situation. The present review describes thirstiness and hydration, the food products and beverages that cause thirstiness, and the beverages and food products currently available to quench thirstiness in individuals with restricted access to liquid ingestion. It also discusses how to measure the effectiveness of calming thirstiness. To diminish thirstiness distress, different alternatives to liquids are proposed. Individuals with swallowing disorders are given thickened water, individuals with restricted water ingestion are given ice cubes or ice popsicles of different flavors, and sportspeople are given energy gels. However, current beverage solutions seem not to relieve thirst fully, although some stimuli like iced water, flavors (especially lemon and mint), or acids seem to work better than plain stimuli and could be added to existing products. Therefore, there is still a need to incorporate these strategies into beverage and food formulations and to test their effectiveness.

Effects of Water Restriction and Supplementation on Cognitive Performances and Mood among Young Adults in Baoding, China: A Randomized Controlled Trial (RCT)

The brain is approximately 75% water. Therefore, insufficient water intake may affect the cognitive performance of humans. The present study aimed to investigate the effects of water restriction and supplementation on cognitive performances and mood, and the optimum amount of water to alleviate the detrimental effects of dehydration, among young adults. A randomized controlled trial was conducted with 76 young, healthy adults aged 18–23 years old from Baoding, China. After fasting overnight for 12 h, at 8:00 a.m. of day 2, the osmolality of the first morning urine and blood, cognitive performance, and mood were measured as a baseline test. After water restriction for 24 h, at 8:00 a.m. of day 3, the same indexes were measured as a dehydration test. Participants were randomly assigned into four groups: water supplementation group (WS group) 1, 2, or 3 (given 1000, 500, or 200 mL purified water), and the no water supplementation group (NW group). Furthermore, participants were instructed to drink all the water within 10 min. Ninety minutes later, the same measurements were performed as a rehydration test. Compared with the baseline test, participants were all in dehydration and their scores on the portrait memory test, vigor, and self-esteem decreased (34 vs. 27, p < 0.001; 11.8 vs. 9.2, p < 0.001; 7.8 vs. 6.4, p < 0.001). Fatigue and TMD (total mood disturbance) increased (3.6 vs. 4.8, p = 0.004; 95.7 vs. 101.8, p < 0.001) in the dehydration test. Significant interactions between time and volume were found in hydration status, fatigue, vigor, TMD, symbol search test, and operation span test (F = 6.302, p = 0.001; F = 3.118, p = 0.029; F = 2.849, p = 0.043; F = 2.859, p = 0.043; F = 3.463, p = 0.021) when comparing the rehydration and dehydration test. Furthermore, the hydration status was better in WS group 1 compared to WS group 2; the fatigue and TMD scores decreased, and the symbol search test and operation span test scores increased, only in WS group 1 and WS group 2 (p < 0.05). There was no significant difference between them (p > 0.05). Dehydration impaired episodic memory and mood. Water supplementation improved processing speed, working memory, and mood, and 1000 mL was the optimum volume.

A Portable Biodevice to Monitor Salivary Conductivity for the Rapid Assessment of Fluid Status

The evaluation of fluid status can save adults from life-threatening conditions, but the current methods are invasive or time-consuming. Therefore, we developed a portable device for measuring salivary conductivity. This prospective observational study enrolled 20 volunteers with no history of systemic diseases. Participants were observed for 13 h, including water restriction for 12 h followed by rehydration with 1000 mL water within 1 h. Serum and urine biomarkers for fluid status, thirst scales, and salivary conductivity were collected during dehydration and rehydration. No significant differences in age, body mass index, glycohemoglobin, and estimated glomerular filtration rate were noted between sexes. Salivary conductivity increased after water restriction and decreased after rehydration. Similarly, urine osmolality, urine specific gravity, thirst intensity scales, and body weight followed the same trend and were statistically significant. The angiotensin-converting enzyme and aldosterone levels showed the same trend, without reaching statistical significance. The red blood cell count and hemoglobin concentration also followed the same trend. Analyzing the receiver operating characteristic curves, the area under the curve was 0.707 (95% confidence interval 0.542–0.873, p = 0.025). Using the Youden index, the optimal cutoff determined as 2678.09 μs/cm (sensitivity: 90%, specificity: 55%). This biodevice effectively screened dehydration among healthy adults.

Consequences of police-related personal protective equipment and physical training status on thermoregulation and exercise energy expenditure

BACKGROUND

The aim was to examine the impact of personal protective equipment (PPE) on human thermoregulation and its alteration in groups of different training status.

METHODS

45 men performed a maximum voluntary contraction test in an upright pull position to determine lower body strength and a graded treadmill test to determine maximum oxygen uptake (VO2max). Body composition was estimated via bioelectric impedance analysis. According to specific cutoff values, participants were assigned to a group of endurance-trained, strength-trained, endurance- and strength-trained, or untrained individuals. Subsequently, they completed two graded exercise tests until volitional exhaustion, once wearing sports wear (SPW) and once wearing PPE (20.9 kg). Participants were weighed before and afterward to investigate sweat loss and sweat rate. Body temperature was measured continuously from the tympanic membrane. Energy expenditure was derived from breathing gas analysis.

RESULTS

Sweat rate was 91% higher in PPE than in SPW but not significantly differnt between groups (p > 0.05). Body temperature was significantly higher in PPE during submaximal (+1.14 ± 0.45 °C) and maximal exercise intensity (+0.68 ± 0.57 °C) and was poorely related to VO2max and body composition. Energy expenditure significantly differed between both garments (+37% in PPE) and groups (p < 0.05). Additionally, energy expenditure significantly correlated with body weight (r = 0.84 in SPW and r = 0.68 in PPE).

CONCLUSIONS

Strength training alone does not seem to have any or negligible effects on thermoregulation. Endurance training and weight management might lead to rather small improvements in heat tolerance.

Does Hydration Status Influence Executive Function? A Systematic Review

BACKGROUND

Cognitive function, including executive function (EF)-related capacities (eg, working memory, inhibitory and attentional control), has been linked to adherence to healthy lifestyle behaviors. Dehydration is associated with impaired cognitive function, whereas improvements in hydration status may improve inhibitory and attentional performance. No systematic reviews have examined the effects of both dehydration and euhydration on EF.

OBJECTIVE

The objectives of this systematic review are to examine studies that have investigated the spectrum of hydration status and EF in adults, and to identify future research needs.

DESIGN

The review was conducted according to the 2015 Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) guidelines. The database search was initially conducted on May 12, 2019 and then updated on April 26, 2020. Databases searched included PubMed, Medline, Psyc Info, SCOPUS, Proquest, and ISI Web of Science. Data extraction included the following: method used to assess de/hydration status, study design, participant characteristics, EF tasks and domain, and results. Article quality ratings were performed on included studies using the Academy of Nutrition and Dietetics Quality Rating Checklist.

PARTICIPANTS/SETTING

Studies done with healthy or diseased adults, aged older than 18 years, in any setting, were included. Studies of individuals with disease states that impact fluid balance or require fluid restrictions as treatments were excluded.

MAIN OUTCOME MEASURE

All EF-related outcomes were included, such as working memory, inhibitory control, task switching, and attention.

RESULTS

Four thousand eight hundred thirty-three articles were screened using title/abstracts. Seventy-one full-text articles were assessed for eligibility; 33 were included (26 included investigations of dehydration; 27 included investigations of rehydration/euhydration) with 3,636 participants across all studies. Little consistency was found across outcomes. Roughly half of the available studies suggested unclear or neutral EF effects, and half suggested effects on EF domains, particularly working memory, inhibitory control, and attention. Studies including a euhydration condition were slightly more likely to demonstrate improvements to EF capacities.

CONCLUSIONS

Overall, there is a strong need for consistent methodological approaches and a greater number of long-term (ie, >3 days) studies of dehydration and euhydration and EF.

Different Amounts of Water Supplementation Improved Cognitive Performance and Mood among Young Adults after 12 h Water Restriction in Baoding, China: A Randomized Controlled Trial (RCT)

Water is indispensable to keeping the functions of the human body working properly, including that of the brain. The purpose of this research was to explore the impacts of water supplementation on cognitive performance and mood, and to determine the optimum amount of water to alleviate detriments of dehydration after 12 h water restriction. A randomized controlled trial was implemented among 64 young adults from Baoding, China. Fasting overnight for 12 h, and at 8:00 a.m. on day 2, osmolality of first morning urine and blood, cognitive performance, and mood were assessed as the dehydration test. Then, participants were randomly separated into four groups: water supplementation groups (WS groups 1, 2, and 3 with 500, 200, and 100 mL purified water, respectively) and no water supplementation group (NW group). Participants in WS groups were instructed to drink the water within 10 min, while those in NW group drank no water. After 90 min, the same measurements were taken as the rehydration test. There was significant interaction between TIME and VOLUME in thirst when comparing dehydration with rehydration tests (F = 6.172, p = 0.001). Significant thirst reductions were found in WS group 1 and WS group 2 (p = 0.003; p = 0.041), and a significant increase was found in the NW group (p = 0.039). In the rehydration test, significant interactions between TIME and VOLUME were found in scores of anger, fatigue, and TMD (total mood disturbance) (F = 3.815, p = 0.014; F = 10.429, p < 0.001; F = 5.246, p < 0.001), compared to the dehydration test. Scores of anger were only decreased in WS group 2 (p = 0.025), and scores of fatigue and TMD decreased in WS group 1 and WS group 2 (all p < 0.05). Significant interaction between TIME and VOLUME was only found for operation span test scores (F = 2.816, p = 0.047), with scores being only higher in WS group 1 in the rehydration test compared to the dehydration test (p = 0.003). Comparing WS group 1 and WS group 2, scores of thirst, fatigue, and TMD did not differ significantly (p > 0.05). Water supplementation improved working memory and attenuated anger, fatigue, and TMD. A small amount of water (200 mL) was sufficient to attenuate thirst, anger, fatigue, and TMD of young adults, but the larger volume (500 mL) appeared to be necessary to improve working memory. The amount of 500 mL was the optimum volume to improve the cognitive performance and mood among young adults.

Progression of human subjective perceptions during euhydration, mild dehydration, and drinking

Thirst motivates consumption of water necessary for optimal health and cognitive-physiological functions. Other than thirst, little is known about coexisting perceptions and moods that provide information to the brain and participate in body water homeostasis. The purpose of this investigation was to observe perceptions, somatic sensations, and moods during controlled changes of hydration status. During routine daily activities interspersed with laboratory visits, 18 healthy young men (age, 23±3 y; body mass, 80.13±10.61 kg) self-reported hourly ratings (visual analog scales, VAS) of 17 subjective perceptions, across two 24-h periods (ad libitum food and water intake while euhydrated; water restriction with dry food intake [WR]) and during a 30-min rehydration session (R₃₀, 1.46±0.47 L water intake). At the end of WR, body mass loss reached 1.67 kg (2.12%). Distinct perceptions were identified during euhydration, WR and immediately after R₃₀. Starting approximately 4 h after WR began (body mass loss of ∼0.5%), perceptual changes included progressively intensifying ratings of thirst, mouth dryness, desire for water, and pleasantness of drinking. In comparison, immediately after R₃₀, participants reported a reversal of the perceptions observed during WR (above) plus cooler thermal sensation, increased satisfaction, and stomach fullness. These VAS ratings suggested that aversive moods contributed to drinking behavior and supported previously published animal studies. In conclusion, this investigation delineates previously unreported perceptions and their evolution (e.g., appearance, extinction, time course) that motivated drinking during WR and discouraged overdrinking after R₃₀.

Water Consumption during a School Day and Children's Short-Term Cognitive Performance: The CogniDROP Randomized Intervention Trial

There is still little research examining the relationship between water consumption in school and specific cognitive performance. The aim of this cluster-randomized intervention CogniDROP trial was to investigate the short-term effects of drinking water during the morning on executive functions. The participants were from the 5^th and 6^th grade of a comprehensive school in Germany (14 classes, n = 250, 61.6% boys). The classes were randomly divided into an intervention group (an education on healthy drinking behavior and a promotion of water consumption) and a control group. A battery of computerized tasks (Switch Task, 2-Back Task, Corsi Block-Tapping Task and Flanker Task) was used to test executive functions. Urine color and thirst were evaluated to check the hydration level. Physical activity over the past 24 h was measured using GT3X ActiGraph. A non-linear relationship was observed between the amount of drinking water and executive performance. Consuming water up to 1000 mL (or up to 50% of Total Water Intake) had benefits during memory tasks. Urine color and number of steps on the study day correlated with water consumed. The results suggest that a water-friendly environment supports school-aged children in adequate water intake resulting in better cognitive performance, especially short-term memory.

Hydration Status and Cardiovascular Function

Hypohydration, defined as a state of low body water, increases thirst sensations, arginine vasopressin release, and elicits renin–angiotensin–aldosterone system activation to replenish intra- and extra-cellular fluid stores. Hypohydration impairs mental and physical performance, but new evidence suggests hypohydration may also have deleterious effects on cardiovascular health. This is alarming because cardiovascular disease is the leading cause of death in the United States. Observational studies have linked habitual low water intake with increased future risk for adverse cardiovascular events. While it is currently unclear how chronic reductions in water intake may predispose individuals to greater future risk for adverse cardiovascular events, there is evidence that acute hypohydration impairs vascular function and blood pressure (BP) regulation. Specifically, acute hypohydration may reduce endothelial function, increase sympathetic nervous system activity, and worsen orthostatic tolerance. Therefore, the purpose of this review is to present the currently available evidence linking acute hypohydration with altered vascular function and BP regulation.