A drink of water can improve or impair mental performance depending on small differences in thirst

Evolution of the thirst mechanism in Homo: The need and limitations of thirst and hydration

There is a view that the perception of thirst and actual body fluid balance may affect cognitive and exercise performance. The evolutionary evidence suggests that our survival was dependent on our ability to sweat profusely when hunting during the heat of the day (persistence hunting), so if water deficits were not tolerated, consequently the thirst mechanism would limit our persistence hunting capability. This also means that hunting and searching for water was undertaken with some extent of water deficit, and in turn suggests that performance; physical and cognitive, was conducted with a degree of dehydration. Given the current views on the maintenance of body water for performance, there is a need to evaluate the evidence relating to tolerance limits for water deficits with respect to both physical and cognitive performance. This review considers the thirst mechanism and the conditions and selective pressures under which this might have evolved. Consideration will be given to how the thirst mechanism influences our physical and cognitive performance. The review suggests that Homo developed appropriate tolerances for water deficits and thirst perception, with a safety margin that prevented detrimental declines in physical and cognitive performance to the point of inhibiting corrective action. This would have offered a selective advantage, enabling the search for water and functioning adequately during periods of water scarcity.

Association between Anxiety Status and Hydration Status in Spanish University Students

Anxiety disorders are a very common psychiatric pathology among young university students, and the strategies for its mitigation are limited to the consumption of anxiolytic substances. Adequate hydration is essential for staying healthy, as water is the main component of the human body and of several physiological processes. A state of dehydration, in addition to a negative water balance, has serious consequences on health status. We aimed to determine the association between the degree of anxiety and the level of hydration in Spanish university students. A cross-sectional, observational research study with a sample of 65 female university students was conducted. Over 90% of the study population shows anxiety levels above the 95th percentile. The individuals with anxiety above the 95th percentile showed a negative water balance. The consumption of coffee and herbal teas shows correlations with state anxiety and trait anxiety.

Cold Suggestion to Cope with the Negative Impact of Tropical Climate

The thermal discomfort experienced in a tropical environment has negative effects on human performance. Cooling techniques before, during, or immediately after exercise have been extensively reported on in the physiological literature, but psychological techniques for subjective cooling have rarely been explored. The purpose of this experiment was to evaluate whether a cold suggestion would have an effect on environmental perceptions and affect in a tropical climate. Fifty participants were assigned in random order to two experimental sessions in similar hot and humid conditions at a 1-week interval (30°C ± 1.2; 87% rH ± 2): one with a suggestion focused on cold and the other a control session. The main results indicated that the suggestion focused on cold significantly decreased thermal discomfort and perceived heat and reduced the degradation on the Feeling Scale. The cold suggestion used as a per-cooling technique to cope with the negative impact of a tropical climate is discussed.

Hydration and meal habits of physicians and medical learners: a literature review

PURPOSE

Nutrition and hydration are important components of physician and medical learner well-being; meal-skipping and insufficient hydration are known to negatively impact cognition. Existing data on these phenomena are sparse and rarely considered together; furthermore, there is a lack of literature on interventions to address these problems. We therefore aimed to characterize existing literature on this topic.

METHODS

We conducted a literature review of existing literature on the prevalence of and reasons for meal-skipping and insufficient hydration in physicians and medical learners.

RESULTS

Reported prevalences varied widely, as did the ways in which the data were collected. Reasons for meal-skipping and insufficient hydration are less studied, but a lack of time is the most commonly reported reason, among a variety of other barriers.

CONCLUSION

Further research is required to better characterize the prevalences and reasons for meal-skipping in physicians and medical learners. By consolidating the state of current knowledge on this topic in this work, we establish the groundwork for future studies and allow intervention studies to be based on a broader data set.

The Matrix Matters: Beverage Carbonation Impacts the Timing of Caffeine Effects on Sustained Attention

Both caffeine and the perception of refreshment delivered by cooling, tingling, and mouth-watering flavors have individually been shown to positively impact cognitive performance and mood, though presently there is limited evidence on their possible combined effects. This study explored the contribution of refreshing compounds in beverages, namely, carbon dioxide and citric acid, on the acute effects of caffeine on sustained attention and self-rated physical and mental energy. A randomized, controlled crossover trial was conducted by testing three products: a carbonated caffeinated beverage; a comparator caffeinated beverage; and a flavor-matched control beverage. Findings from 24 healthy adults revealed product-dependent variations in cognitive performance during a 60-min visual sustained-attention task, suggesting that the carbonated-caffeinated beverage led to faster, greater and more consistent levels of accuracy, compared to the control beverage. Specifically, significant differences were found between: (1) the carbonated-caffeinated beverage and the caffeinated beverage, and (2) between the caffeinated beverage and the control beverage for number of hits, reaction time and false alarm scores. Both caffeinated beverages led to higher physical and mental energy, and lower physical and mental fatigue 60-min post-consumption. These findings suggest beneficial effects on sustained attention through the combination of caffeine with refreshing compounds.

Association of Dietary Habits with Mild Cognitive Impairment among Elderly in Rural Area of North China

BACKGROUND

Recent findings suggest a possible role of diet, particularly nutrient intakes and dietary patterns, in the prevalence of mild cognitive impairment (MCI); few studies, however, have been explicitly devoted to the relationship between dietary habits and MCI.

OBJECTIVES

We aimed to explore the association between dietary habits, including meal timing, and MCI among older Chinese adults.

METHODS

This cross-sectional study involved data collected at the baseline of the Tianjin Elderly Nutrition and Cognition Cohort (TENCC) study, in which 3,111 community-dwelling older adults (326 MCI patients and 2,785 non-MCIs) from a rural area of Tianjin, China, were recruited. In March 2018 to June 2019, all participants underwent a detailed neuropsychological evaluation that allowed for psychometric MCI classification. Information on self-reported dietary behaviors was gathered via face-to-face interviews. Crude and multivariable-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression models.

RESULTS

In the multivariable-adjusted models, eating breakfast 4 to 6 times per week (vs. ≤3 times per week, OR: 0.45; 95% CI: 0.26, 0.75), drinking water before breakfast (yes vs. no, OR: 0.64; 95% CI: 0.51, 0.82), consuming water ≥1.5L per day (vs. <1.5L per day, OR: 0.64; 95% CI: 0.51, 0.82), and having lunch after 12:00 (vs. before 12:00, OR: 0.59; 95% CI: 0.47, 0.75) were associated with decreased risk of MCI. Participants who consumed higher amounts of cooking oil were at a higher risk of MCI (moderate vs. low, OR: 1.42; 95% CI: 1.04, 1.92; high vs. low, OR: 1.40; 95% CI: 1.07-1.83).

CONCLUSION

This study suggests that dietary habits, including breakfast frequency, daily water consumption, cooking oil consumption, and meal timing, may be associated with the risk of MCI. If replicated, these findings would open new possibilities of dietary interventions for MCI.

Hydration status, body composition, and anxiety status in aeronautical military personnel from Spain: a cross-sectional study

BACKGROUND

An adequate hydration status is critical to ensure efficiency during mental and physical activities. Our goal was to assess the hydration status of a Spanish group of aeronautical military men and to determine the association of hydration status with body composition and anxiety.

METHODS

A total of 188 men were evaluated through a validated hydration questionnaire, anthropometric and biochemical parameters, and an anxiety questionnaire. Based on these methods, the criteria of hydration were established.

RESULTS

Of the total sample, 81% met the hydration criteria (urine color = well hydrated, water balance ≥ 0 ml, and total water intake/weight ≥ 35 ml/kg), and 19% did not meet the hydration criteria (urine color = not sufficiently hydrated or dehydrated, water balance < 0 ml, and total water intake/weight < 35 ml/kg). Subjects not meeting the hydration criteria had lower urine pH, negative water balance, and lower water intake. The latter also had higher anxiety status (score = 4 vs. 3, P = 0.026), weight [(84.7 ± 10.5) vs. (80.5 ± 10.2) kg], body mass index [(26.3 ± 3.1) vs. (25.2 ± 2.8)]kg/m2, body fat [(22.3 ± 5.6) vs. (18.3 ± 6.5)] %, urine specific gravity, and urine color. Using a logistic binary regression model, hydration status was related significantly with the percentage of body fat (P = 0.004), but no relation was found with age, comorbidities, or medications. Furthermore, total water intake/weight was positively correlated with percentage of body water (r = 0.357, P = 0.000) and negatively with body fat (kg) (r = - 0.427, P = 0.000), percentage of body fat (r = - 0.405, P = 0.000), and waist/hip ratio (r = - 0.223, P = 0.002). Based on a linear regression model, total water intake/weight was related significantly with percentage of body fat (P = 0.001) and percentage of body water content (P = 0.035). No relation was found, however, with waist/hip ratio, age, comorbidities, or medications.

CONCLUSIONS

These findings all suggest a relationship between hydration status and body composition but also set the bases for future studies that relate hydration status and anxiety status. These results can be used to improve the hydration status and body composition of military personnel.

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.

Impact of Cold Water Intake on Environmental Perceptions, Affect, and Attention Depends on Climate Condition

The use of cooling techniques in a tropical climate can limit the increase in core body temperature and therefore improve physical exercise performance. However, little is known about the impact of cooling on psychological functioning. The aim of this study was to determine whether cold water intake influences environmental perceptions, affects, and attention depending on the climate condition (tropical climate vs. neutral climate). The study followed a mixed 2 × 3 crossover design (climate as the within factor, tropical climate vs. neutral climate; water intake as the between factor, cold water vs. neutral water vs. no water). Participants reported lower thermal comfort, had positive affect scores, had lower attention performance scores, and had higher thermal sensation and negative affect in tropical climate compared with neutral climate. It was shown that drinking water at room temperature in a neutral climate causes the best thermal comfort scores, and drinking water at room temperature in tropical climate causes the worst scores. Cold water intake, which had no notable influence on positive affect scores in a tropical climate, had a deleterious effect in a neutral climate. Drinking cold water as a technique to limit the deleterious effects of tropical climate on environmental perceptions, affect, and attention is discussed.

Autonomic adaptations mediate the effect of hydration on brain functioning and mood: Evidence from two randomized controlled trials

Dehydration (water loss >2.0% of body weight) has significant negative effects on physical and mental performance. In two studies the effects of minor hypo-hydration (water loss <1.0% of body weight) on CNS function, mood and cardiovascular functioning were measured. Study 1: On two mornings twelve male participants were exposed to a temperature of 30 °C for four hours and either did or did not drink two 150 ml glasses of water during that time. Study 2: Fifty-six (25 M) individuals were exposed to the same 30 °C environment and randomly allocated to either drink (2 × 150 ml) or not drink. When not given water 0.59% (Study 1) and 0.55% (Study 2) bodyweight was lost. Participant’s heart rate variability (HRV) was measured, and they rated their thirst and mood. In study 1, participants participated in an fMRI protocol during which they completed a modified version of the Paced Auditory Serial Addition Test (PASAT), at the end of which they rated its difficulty. Decreases in fMRI BOLD activity in the orbito-frontal cortex, ventral cingulate gyrus, dorsal cingulate cortex, hypothalamus, amygdala, right striatum, post-central gyrus and superior parietal cortex were observed when participants were hypo-hydrated. These deactivations were associated with reduced HRV, greater perceived effort, and more anxiety. In study 2 declines in HRV were found to mediate the effect of hypo-hydration on ratings of anxiety. These data are discussed in relation to a model that describes how autonomic regulatory and interoceptive processes may contribute to the affective consequences of minor hypo-hydration.

At what stage in the drinking process does drinking water affect attention and memory? Effects of mouth rinsing and mouth drying in adults

Drinking water is important for health and there is an agreement that drinking water facilitates certain cognitive processes. However, the mechanism underlying the effect of drinking water on cognition is unknown. While attention performance is improved by even a very small drink, memory performance seems to require larger drinks for performance enhancement. This suggests that attention could be affected earlier in the drinking process than memory. We aimed to elucidate further the mechanism involved by investigating the stage during the drinking process influencing performance on cognitive tasks. To this end, we compared mouth rinsing and mouth drying. Mouth rinsing was expected to result in improved attention performance and would suggest that the mechanism responsible is located in the mouth and occurs early in the drinking process, before swallowing. Eighty-seven adults participated in either a treatment (mouth rinsing or mouth drying) or control (no intervention) condition. They were assessed at baseline and 20 min later after intervention on measures of visual attention, short-term memory, subjective thirst and mood. Our results showed that mouth rinsing improved visual attention, but not short-term memory, mood or subjective thirst. Mouth drying did not affect performance. Our results support the hypothesis that different mechanisms underlie the effect of drinking water on different cognitive processes. They suggest that merely sipping water, as opposed to having a large drink, can improve attention.

Water supplementation after dehydration improves judgment and decision-making performance

Previous research has shown that dehydration and water supplementation affect mood and cognitive performance in both adults and children on a variety of tasks that assess memory, attention, executive function, and speeded responses. Given the varied effects of water on cognition, this study explored potential effects of water supplementation, hydration status, and thirst on thinking and decision-making tasks. 29 adult participants undertook a battery of cognitive tests on two separate occasions after having fasted from the previous night. On one occasion, they were offered 500 ml of water to drink prior to testing. Measures of urine osmolality confirmed the group-level effectiveness of the dehydration manipulation. Water supplementation was found to improve performance on tasks measuring cognitive reflection in judgement and decision-making. This increase in performance was associated with differences in tasks implicated in inhibition processes. Drinking water after a 12-h dehydration period increased performance in judgement and decision-making tasks, and this was not explained by differences in subjective thirst or attentiveness.

The impact of water consumption on hydration and cognition among schoolchildren: Methods and results from a crossover trial in rural Mali

Adequate provision of safe water, basic sanitation, and hygiene (WASH) facilities and behavior change can reduce pupil absence and infectious disease. Increased drinking water quantity may also improve educational outcomes through the effect of hydration on attention, concentration, and short-term memory. A pilot study was conducted to adapt field measures of short-term cognitive performance and hydration, to evaluate levels of hydration, and to investigate the impact of providing supplementary drinking water on the cognitive performance of pupils attending water-scarce schools in rural Mali. Using a cross-over trial design, data were collected under normal school conditions (control condition) on one visit day; on the other, participants were given a bottle of water that was refilled throughout the day (water condition). Morning and afternoon hydration was assessed using specific gravity and urine color. Cognitive performance was evaluated using six paper-based tests. Three percent of pupils were dehydrated on the morning of each visit. The prevalence of dehydration increased in the afternoon, but was lower under the water condition. Although there was a trend indicating drinking water may improve cognitive test performance, as has been shown in studies in other settings, results were not statistically significant and were masked by a "practice effect."

Narrative Review of Hydration and Selected Health Outcomes in the General Population

Although adequate hydration is essential for health, little attention has been paid to the effects of hydration among the generally healthy population. This narrative review presents the state of the science on the role of hydration in health in the general population, specifically in skin health, neurological function (i.e., cognition, mood, and headache), gastrointestinal and renal functions, and body weight and composition. There is a growing body of evidence that supports the importance of adequate hydration in maintaining proper health, especially with regard to cognition, kidney stone risk, and weight management. However, the evidence is largely associative and lacks consistency, and the number of randomized trials is limited. Additionally, there are major gaps in knowledge related to health outcomes due to small variations in hydration status, the influence of sex and sex hormones, and age, especially in older adults and children.

Effect of Water Supplementation on Cognitive Performances and Mood among Male College Students in Cangzhou, China: Study Protocol of a Randomized Controlled Trial

Introduction: Water accounts for about 75% of brain mass. Cognitive performances and mood may be impaired by hypohydration and improved by water supplementation. Two surveys conducted in China demonstrated that a large proportion of adults and children drank less fluid than the amounts recommended by the Chinese Nutrition Society. The association between hypohydration and cognitive performance has not been reported in China. The purpose of this study is to explore the effect of water supplementation on cognitive performances and mood among male college students in Cangzhou, China. Methods and Analysis: A randomized controlled trial is designed to test the hypothesis. A total of 68 male college students aged 18–25 years will be recruited and randomly assigned into water-supplementation group (WS group, n = 34) and no water-supplementation group (NW group, n = 34) after an overnight fasting, i.e., without eating foods and drinking fluid for 12 h. The first morning urine will be collected to determine urine osmolality on the water supplementation day. Cognitive performances and mood will be performed before water supplementation by researchers with questionnaire. Subjects in the WS group will drink 400 mL purified water within 5 min, while those in NW group will not drink any fluid. One hour later, urine will be collected and urine osmolality, cognitive performances and mood will be measured again. Mixed model of repeated measures ANOVA will be used to investigate the effect of water supplementation on cognitive performances. The study would provide information about the benefit of water supplementation on cognitive performances. Ethics and Dissemination: The study protocol is reviewed and approved by the Ethical Review Committee of the Chinese Nutrition Society. Ethical approval project identification code is CNS-2015-001. Results will be published according to the CONSORT statement and will be reported in peer-reviewed journals. Trial registration: Chinese clinical trial registry. Identifier: ChiCTR-IOR-15007020. Registry name “The effect of hydration on cognitive performance”.

Thirst at Work Implies More Than Just Inadequate Facilities for Breaks

Early signs of dehydration, such as headaches, are not unusual in the working population. Even slight deficiencies of water intake may have negative effects on both health and performance. However, little is known about work-related fluid intake. We expect the daily experience of interruptions to distract from perceived thirst, resulting in reduced daily fluid intake. This effect may be more pronounced when the workload is generally less predictable due to the assignment of tasks that are beyond the definition of the worker's professional role (unreasonable tasks). Data were gathered from 29 female service employees across five workdays. Multilevel analyses revealed daily work interruptions to be negatively associated with fluid intake, especially when there were frequent unreasonable task-assignments. Results suggest that interruptions at work might reduce daily fluid intake. However, adequate allocation of tasks by managers can protect employees against insufficient drinking.

Dose-response effects of water supplementation on cognitive performance and mood in children and adults

Water supplementation has been found to facilitate visual attention and short-term memory, but the dose required to improve performance is not yet known. We assessed the dose response effect of water on thirst, mood and cognitive performance in both adults and children. Participants were offered either no water, 25 ml or 300 ml water to drink. Study 1 assessed 96 adults and in Study 2, data are presented from 60 children aged 7-9 years. In both studies, performance was assessed at baseline and 20 min after drinking (or no drink); on thirst and mood scales, letter cancellation and a digit span test. For both children and adults, a large drink (300 ml) was necessary to reduce thirst, while a small drink (25 ml) was sufficient to improve visual attention (letter cancellation). In adults, a large drink improved digit span, but there was no such effect in children. In children, but not adults, a small drink resulted in increased thirst ratings. Both children and adults show dose-response effects of drinking on visual attention. Visual attention is enhanced by small amounts of fluid and appears not to be contingent on thirst reduction. Memory performance may be related to thirst, but differently for children and adults. These contrasting dose-response characteristics could imply cognitive enhancement by different mechanisms for these two domains.

Infusing pleasure: Mood effects of the consumption of a single cup of tea

Tea has historically been associated with mood benefits. Nevertheless, few studies have empirically investigated mood changes after tea consumption. We explored immediate effects of a single cup of tea up to an hour post-consumption on self-reported valence, arousal, discrete emotions, and implicit measures of mood. In a parallel group design, 153 participants received a cup of tea or placebo tea, or a glass of water. Immediately (i.e. 5 min) after consumption, tea increased valence but reduced arousal, as compared to the placebo. There were no differences at later time points. Discrete emotions did not differ significantly between conditions, immediately or over time. Water consumption increased implicit positivity as compared to placebo. Finally, consumption of tea and water resulted in higher interest in activities overall and in specific activity types compared to placebo. The present study shows that effects of a single cup of tea may be limited to an immediate increase in pleasure and decrease in arousal, which can increase interest in activities. Differences between tea and water were not significant, while differences between water and placebo on implicit measures were unexpected. More servings over a longer time may be required to evoke tea's arousing effects and appropriate tea consumption settings may evoke more enduring valence effects.

Effects of Water Provision and Hydration on Cognitive Function among Primary-School Pupils in Zambia: A Randomized Trial

There is a well-established link between hydration and improved cognitive performance among adults, with evidence of similar findings among children. No trials have investigated the impact of water provision on cognitive performance among schoolchildren in hot and arid low-resource settings. We conducted a randomized-controlled trial in five schools with limited water access in Chipata district in Eastern province, Zambia, to assess the efficacy of water provision on cognition. Pupils in grades 3–6 were randomly assigned to either receive a bottle of drinking water that they could refill throughout the day (water group, n = 149) or only have access to drinking water that was normally available at the school (control group, n = 143). Hydration was assessed in the morning before provision of water and in the afternoon through urine specific gravity (U_sg) measured with a portable refractometer. In the afternoon we administered six cognitive tests to assess short-term memory, concentration, visual attention, and visual motor skills. Morning prevalence of dehydration, defined as U_sg≥1.020, was 42%. Afternoon dehydration increased to 67% among the control arm and dropped to 10% among the intervention arm. We did not find that provision of water or hydration impacted cognitive test scores, although there were suggestive relationships between both water provision and hydration and increased scores on tests measuring visual attention. We identified key improvements to the study design that are warranted to further investigate this relationship.

Trial Registration: ClinicalTrials.gov NCT01924546

Hydration status moderates the effects of drinking water on children's cognitive performance

Changes in hydration status throughout the day may affect cognitive performance with implications for learning success in the classroom. Our study tested the hypothesis that the benefit of drinking water on working memory and attention depends upon children's hydration status and renal response to water intake. Fifty-two children aged 9-12 years old were tested under two experimental conditions. The treatment session (Water session) consisted of a standard breakfast with 200 ml water, a baseline test, consumption of 750 ml of water over a period of two hours and subsequently retested. No water was provided after breakfast during the control session. Changes in hydration were assessed via urine samples. Cognitive testing consisted of digit span, pair cancellation, and delayed match to sample tasks. Children who exhibited smaller decreases in urine osmolality following water intake performed significantly better on the water day compared to the control day on a digit-span task and pair-cancellation task. Children who exhibited larger decreases in urine osmolality following water intake performed better on the control day compared to the water day on the digit-span task and pair-cancellation task. These results suggest that focusing on adequate hydration over time may be key for cognitive enhancement.

Hydration amongst nurses and doctors on-call (the HANDS on prospective cohort study)

BACKGROUND & AIMS

Dehydration of as little 2% of total body weight may impair physical and cognitive performance. The aim of this study was to investigate the prevalence of dehydration at the start and end of shifts in nurses and doctors on-call. The secondary aims were to assess the relation between hydration status and cognitive function.

METHODS

This prospective cohort study was conducted on nurses and doctors working on medical and surgical admissions wards at a university teaching hospital. Participants arrived on the ward approximately 20 min before their shift and were asked to provide a urine sample. Height and weight were then measured. A 10 mL blood sample was analysed for full blood count, serum urea and electrolytes, and blood glucose. Cognitive function was assessed using a series of computer-based tests including the Stroop Colour Naming Interference Test and Sternberg Memory Paradigm. Participants then worked normally but were asked to keep a fluid diary for the duration of their shift and fluid balance was estimated. Tests were repeated at the end of the shift. Dehydration was defined as urine osmolality >800 mOsmol/kg and oliguria was defined as urine output <0.5 ml/kg/hour.

RESULTS

We recruited 92 nurses and doctors, of whom 88 completed the study, amounting to 130 shifts. 52% participated for one shift, and 48% for two shifts. Thirty-six percent of participants were dehydrated at the start of the shift and 45% were dehydrated at the end of their shift. Mean (SD) urinary osmolality was significantly greater at the end of the shift when compared with the start [720 (282) vs. 622 (297) mOsm/kg, P = 0.031). Moreover, 41% were oliguric at the end of the shift. Single number and five-letter Sternberg short-term memory tests were significantly impaired in dehydrated participants (P < 0.05).

CONCLUSIONS

This study highlights that a significant proportion of nurses and doctors were dehydrated at the start and end of medical and surgical shifts. Dehydration was associated with some impairment of cognitive function.

Effects of changes in water intake on mood of high and low drinkers

Objective

To evaluate the effects of a change in water intake on mood and sensation in 22 habitual high-volume (HIGH; 2-4 L/d) and 30 low-volume (LOW; <1.2 L/d) drinkers who were asked to respectively decrease and increase their daily water intake.

Method

During baseline HIGH consumed 2.5 L and LOW 1 L of water/day. During 3 controlled intervention days HIGH's water intake was restricted to 1 L/day whereas LOW's was increased to 2.5 L water/day. Several mood scales (Bond & Lader Visual Analog Scale (VAS), Profile of Mood States, Karolinska Sleepiness Scale, Thirst & Emotional VAS) were administered at different time points during the study. ANOVA including intervention, time point and intervention by time point as fixed effects on mean values (i.e.; baseline data vs. mean of 3 intervention days) for each mood scale was performed.

Results

At baseline HIGH and LOW were comparable in mood state, except for thirst scores (estimate = 17.16, p<0.001) and POMS depression-dejection scores (estimate = 0.55, p<0.05) which were both higher in the HIGH vs. LOW. In HIGH the restricted water intake resulted in a significant increase in thirst (p<0.001) and a decrease in contentedness (p<0.05), calmness (p<0.01), positive emotions (p<0.05) and vigor/activity (p<0.001). In LOW, increased water consumption resulted in a significant decrease in fatigue/inertia (p<0.001), confusion/bewilderment (p = 0.05) and thirst (p<0.001) and a trend to lower sleepiness (p = 0.07) compared to baseline.

Conclusion

Increasing water intake has beneficial effects in LOW, especially sleep/wake feelings, whereas decreasing water intake has detrimental effects on HIGH's mood. These deleterious effects in HIGH were observed in some sleep/wake moods as well as calmness, satisfaction and positive emotions.

Effects of hydration status on cognitive performance and mood

Although it is well known that water is essential for human homeostasis and survival, only recently have we begun to understand its role in the maintenance of brain function. Herein, we integrate emerging evidence regarding the effects of both dehydration and additional acute water consumption on cognition and mood. Current findings in the field suggest that particular cognitive abilities and mood states are positively influenced by water consumption. The impact of dehydration on cognition and mood is particularly relevant for those with poor fluid regulation, such as the elderly and children. We critically review the most recent advances in both behavioural and neuroimaging studies of dehydration and link the findings to the known effects of water on hormonal, neurochemical and vascular functions in an attempt to suggest plausible mechanisms of action. We identify some methodological weaknesses, including inconsistent measurements in cognitive assessment and the lack of objective hydration state measurements as well as gaps in knowledge concerning mediating factors that may influence water intervention effects. Finally, we discuss how future research can best elucidate the role of water in the optimal maintenance of brain health and function.

Subjective thirst moderates changes in speed of responding associated with water consumption

Participants (N = 34) undertook a CANTAB battery on two separate occasions after fasting and abstaining from fluid intake since the previous evening. On one occasion they were offered 500 ml water shortly before testing, and on the other occasion no water was consumed prior to testing. Reaction times, as measured by Simple Reaction Time (SRT), were faster on the occasion on which they consumed water. Furthermore, subjective thirst was found to moderate the effect of water consumption on speed of responding. Response latencies in the SRT task were greater under the “no water” condition than under the “water” condition, but only for those participants with relatively high subjective thirst after abstaining from fluid intake overnight. For those participants with relatively low subjective thirst, latencies were unaffected by water consumption, and were similarly fast as those recorded for thirsty participants who had consumed water. These results reveal the novel finding that subjective thirst moderates the positive effect of fluid consumption on speed of responding. The results also showed evidence that practice also affected task performance. These results imply that, for speed of responding at least, the positive effects of water supplementation may result from an attenuation of the central processing resources consumed by the subjective sensation of thirst that otherwise impair the execution of speeded cognitive processes.

Effects of drinking supplementary water at school on cognitive performance in children

We investigated the beneficial effects of drinking supplementary water during the school day on the cognitive performance and transitory subjective states, such as fatigue or vigor, in 168 children aged between 9 and 11years who were living in a hot climate (South Italy, Sardinia). The classes were randomly divided into an intervention group, which received water supplementation, and a control group. Dehydration was determined by urine sampling and was defined as urine osmolality greater than 800mOsm/kg H(2)O (Katz, Massry, Agomn, & Toor, 1965). The change in the scores from the morning to the afternoon of hydration levels, cognitive performance and transitory subjective states were correlated. In line with a previous observational study that evaluated the hydration status of school children living in a country with a hot climate (Bar-David, Urkin, & Kozminsky, 2005), our results showed that a remarkable proportion of children were in a state of mild, voluntary dehydration at the beginning of the school day (84%). We found a significant negative correlation between dehydration and the auditory number span, which indicates a beneficial effect of drinking supplementary water at school on short-term memory. Moreover, there was a positive correlation between dehydration and performance in the verbal analogy task. The results are discussed in the light of the complexity of the neurobiological mechanisms involved in the relationship between hydration status and cognition.

The effect of glucose dose and fasting interval on cognitive function: a double-blind, placebo-controlled, six-way crossover study

RATIONALE

Previous research has identified a number of factors that appear to moderate the behavioural response to glucose administration. These include physiological state, dose, types of cognitive tasks used and level of cognitive demand. Another potential moderating factor is the length of the fasting interval prior to a glucose load.

OBJECTIVES

Therefore, we aimed to examine the effect of glucose dose and fasting interval on mood and cognitive function.

METHODS

The current study utilised a double-blind, placebo-controlled, balanced, six period crossover design to examine potential interactions between length of fasting interval (2 versus 12 hours) and optimal dose for cognition enhancement.

RESULTS

Results demonstrated that the higher dose (60 g) increased working memory performance following an overnight fast, whereas the lower dose (25 g) enhanced working memory performance following a 2-h fast.

CONCLUSIONS

The data suggest that optimal glucose dosage may differ under different conditions of depleted blood glucose resources. In addition, glucoregulation was observed to be a moderating factor. However, further research is needed to develop a model of the moderating and mediating factors under which glucose facilitation is best achieved.

The Expanding Spectrum of Health Risks: Public Health or Harm?

Drawing on hydration as an illustrative case in point, this review discusses evidence-based perspectives on the continually expanding spectrum of promulgated health risks, including potential benefits and harms to public health. Future directions for inquiry and practice also are addressed.

Dehydration influences mood and cognition: a plausible hypothesis?

The hypothesis was considered that a low fluid intake disrupts cognition and mood. Most research has been carried out on young fit adults, who typically have exercised, often in heat. The results of these studies are inconsistent, preventing any conclusion. Even if the findings had been consistent, confounding variables such as fatigue and increased temperature make it unwise to extrapolate these findings. Thus in young adults there is little evidence that under normal living conditions dehydration disrupts cognition, although this may simply reflect a lack of relevant evidence. There remains the possibility that particular populations are at high risk of dehydration. It is known that renal function declines in many older individuals and thirst mechanisms become less effective. Although there are a few reports that more dehydrated older adults perform cognitive tasks less well, the body of information is limited and there have been little attempt to improve functioning by increasing hydration status. Although children are another potentially vulnerable group that have also been subject to little study, they are the group that has produced the only consistent findings in this area. Four intervention studies have found improved performance in children aged 7 to 9 years. In these studies children, eating and drinking as normal, have been tested on occasions when they have and not have consumed a drink. After a drink both memory and attention have been found to be improved.

Cognitive function in hot environments: a question of methodology

The physiological responses of thermal stress and its consequences on health have been well documented. However, the effect on cognitive function remains equivocal despite a substantial number of studies conducted in the area. Methodological discrepancies across different studies have made it difficult to conclude whether or not heat exposure per se has an adverse effect upon cognitive function and under what specific environmental and physiological conditions these alterations appear. This article gives an overview of the different confounding factors that have made it difficult to make conclusive interpretations. In addition, the current state of knowledge is presented and discussed with reference to the Global Workspace theory. Although previously presented conclusions are promising, much remains to be completed before understanding the mechanisms that could explain the relationship between heat exposure and cognitive function. Finally, recommendations are presented for further research in this area.

Water, hydration, and health

This review examines the current knowledge of water intake as it pertains to human health, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, and the effects of variation in water intake on health and energy intake, weight, and human performance and functioning. Water represents a critical nutrient, the absence of which will be lethal within days. Water's importance for the prevention of nutrition-related noncommunicable diseases has received more attention recently because of the shift toward consumption of large proportions of fluids as caloric beverages. Despite this focus, there are major gaps in knowledge related to the measurement of total fluid intake and hydration status at the population level; there are also few longer-term systematic interventions and no published randomized, controlled longer-term trials. This review provides suggestions for ways to examine water requirements and encourages more dialogue on this important topic.

Voluntary dehydration and cognitive performance in trained college athletes

Cognitive and mood decrements resulting from mild dehydration and glucose consumption were studied. Men and women (total N = 54; M age = 19.8 yr., SD = 1.2) were recruited from college athletic teams. Euhydration or dehydration was achieved by athletes completing team practices with or without water replacement. Dehydration was associated with higher thirst and negative mood ratings as well as better Digit Span performance. Participants showed better Vigilance Attention with euhydration. Hydration status and athlete's sex interacted with performance on Choice Reaction Time and Vigilance Attention. In a second study, half of the athletes received glucose prior to cognitive testing. Results for negative mood and thirst ratings were similar, but for cognitive performance the results were mixed. Effects of glucose on cognition were independent of dehydration.

Does having a drink help you think? 6-7-Year-old children show improvements in cognitive performance from baseline to test after having a drink of water

Little research has examined the effect of water consumption on cognition in children. We examined whether drinking water improves performance from baseline to test in twenty-three 6-7-year-old children. There were significant interactions between time of test and water group (water/no water), with improvements in the water group on thirst and happiness ratings, visual attention and visual search, but not visual memory or visuomotor performance. These results indicate that even under conditions of mild dehydration, not as a result of exercise, intentional water deprivation or heat exposure, children's cognitive performance can be improved by having a drink of water.

The effect of the consumption of water on the memory and attention of children

The impact of asking children to drink water during their school days, and its possible influence on school performance, has been little considered using intervention studies. Therefore in the afternoon the cognitive functioning of 40 children (mean of 8 years and 7 months) was assessed twice, once after drinking 300 ml of water and on another day when no water was provided. Memory was assessed by the recall of 15 previously presented objects. Recall was significantly better on the occasions when water had been consumed. The ability to sustain attention was measured by asking the child to respond to a light that followed an auditory warning after a delay of either 3 or 12 s. The ability to sustain attention was not significantly influenced by whether water had been drunk.

Should children drink more water?: the effects of drinking water on cognition in children

While dehydration has well-documented negative effects on adult cognition, there is little research on hydration and cognitive performance in children. We investigated whether having a drink of water improved children's performance on cognitive tasks. Fifty-eight children aged 7-9 years old were randomly allocated to a group that received additional water or a group that did not. Results showed that children who drank additional water rated themselves as significantly less thirsty than the comparison group (p=0.002), and they performed better on visual attention tasks (letter cancellation, p=0.02; spot the difference memory tasks, ps=0.019 and 0.014).

Glucose administration prior to a divided attention task improves tracking performance but not word recognition: evidence against differential memory enhancement?

RATIONALE

The cognition-enhancing effects of glucose administration to humans have been well-documented; however, it remains unclear whether this effect preferentially targets episodic memory or other cognitive domains.

OBJECTIVES

The effect of glucose on the allocation of attentional resources during memory encoding was assessed using a sensitive dual-attention paradigm.

MATERIALS AND METHODS

One hundred and twenty volunteers (mean age 21.60, SD 4.89, 77 females) took part in this randomised, double-blind, placebo-controlled, parallel groups study where each consumed a 25-g glucose drink or a placebo. Half of the participants in each drink condition attempted to track a moving on-screen target during auditory word presentation. The distance between the cursor and the tracking target was used as an index of attentional cost during encoding. Effects of drink and tracking on recognition memory and drink on tracking performance were assessed. Self-rated appetite and mood were co-monitored.

RESULTS

Co-performing the tracking task significantly impaired memory performance irrespective of drink condition. In the placebo-tracking condition, there was a cost to tracking manifest as greater deviation from target during and immediately following word presentation. Compared with placebo, the glucose drink significantly improved tracking performance during encoding. There were significant time-related changes in thirst and alertness ratings but these were not differentially affected by drink or tracking conditions.

CONCLUSION

Tracking but not memory was enhanced by glucose. This finding suggests that, under certain task conditions, glucose administrations does not preferentially enhance memory performance. One mechanism through which glucose acts as a cognition enhancer is through allowing greater allocation of attentional resources.