Thirst and hydration status in everyday life

The effects of exercise, heat-induced hypo-hydration and rehydration on blood-brain-barrier permeability, corticospinal and peripheral excitability

PURPOSE

The effects of low-intensity exercise, heat-induced hypo-hydration and rehydration on maximal strength and the underlying neurophysiological mechanisms are not well understood.

METHODS

To assess this, 12 participants took part in a randomised crossover study, in a prolonged (3 h) submaximal (60 W) cycling protocol under 3 conditions: (i) in 45 °C (achieving ~ 5% body mass reduction), with post-exercise rehydration in 2 h (RHY2), (ii) with rehydration across 24 h (RHY24), and (iii) a euhydrated trial in 25 °C (CON). Dependent variables included maximal voluntary contractions (MVC), maximum motor unit potential (MMAX), motor evoked potential (MEPRAW) amplitude and cortical silent period (cSP) duration. Blood-brain-barrier integrity was also assessed by serum Ubiquitin Carboxyl-terminal Hydrolase (UCH-L1) concentrations. All measures were obtained immediately pre, post, post 2 h and 24 h.

RESULTS

During both dehydration trials, MVC (RHY2: p < 0.001, RHY24: p = 0.001) and MEPRAW (RHY2: p = 0.025, RHY24: p = 0.045) decreased from pre- to post-exercise. MEPRAW returned to baseline during RHY2 and CON, but not RHY24 (p = 0.020). MEP/MMAX ratio decreased across time for all trials (p = 0.009) and returned to baseline, except RHY24 (p < 0.026). Increased cSP (p = 0.011) was observed during CON post-exercise, but not during RHY2 and RHY24. Serum UCH-L1 increased across time for all conditions (p < 0.001) but was not significantly different between conditions.

CONCLUSION

Our findings demonstrate an increase in corticospinal inhibition after exercise with fluid ingestion, but a decrease in corticospinal excitability after heat-induced hypo-hydration. In addition, low-intensity exercise increases peripheral markers of blood-brain-barrier permeability.Kindly check and confirm inserted city name correctly identified in affiliation 7This is correct.

Thirst in adult patients in the intensive care unit: A scoping review

PURPOSE

To review the literature on thirst in intensive care unit (ICU) patients and report potential causes, risk factors, diagnosis and measurement tools, as well as potential co-occurrence with other distressing symptoms, and the management of thirst in the ICU.

DESIGN

A scoping review employing the Joanna Briggs Institute methodology.

METHODS

PubMed, MEDLINE, EMBASE and CINAHL were searched from inception to April 2024. Any type of empirical study reporting thirst or associated xerostomia in adult patients (≥18 years) admitted to an ICU or high dependency unit for more than 24 h were included.

RESULTS

The search yielded 907 unique records, and after evaluating 65 full-text publications, 21 studies were included. Thirst intensity was addressed most often (eleven studies), whereas the experience (or quality) of thirst and the validation of a measurement instrument, were addressed in only one study. Although co-occurrence of symptoms was addressed in four studies, only one pilot study looked into the interaction of thirst with other symptoms. Intervention studies have been focussing primarily on mouth-care interventions.

CONCLUSION

Thirst is a distressing symptom in the ICU, with reported high prevalence and intensity. Knowledge about its causes, interventions that incorporate minimising its risk, occurrence and intensity are limited.

IMPLICATIONS FOR CLINICAL PRACTICE

Health care providers should acknowledge thirst as a prominent symptom for ICU patients. They should possess knowledge on the factors that potentially evoke or aggravate thirst. Regular and timely relief of thirst by oral care with cold swabs and the application of menthol can be regarded as a first choice of intervention.

Hydration status in adults with metabolic disorders in relation to socioeconomic, lifestyle and health factors

INTRODUCTION

Adequate hydration is essential for maintaining the health and functionality of the human body. This study aimed to examine the association between selected socioeconomic, lifestyle, and health factors and the hydration status of adults with metabolic disorders by analyzing their urine osmolality.

METHODS

The study involved 290 adults aged 18-70 years with metabolic disorders. Separate multivariate logistic regression models were conducted to evaluate the factors associated with urine osmolality in tertiles for women and men. Odds Ratios (OR) and 95% Confidence Intervals (95% CI) were calculated.

RESULTS

In women, the following factors of urine osmolality were identified in 1st tertile: age (OR:1.04), physical activity (moderate/high vs. no/low; OR:0.38), and headaches (no vs. yes; OR:1.55), in 2nd tertile: physical activity (moderate/high vs. no/low; OR:2.46) and fatigue during the day (sometimes vs. never/very rarely; OR:0.45), and in 3rd tertile: age (OR:0.94), professional status ('I work part-time/I study and I work' vs. 'I do not work/I study'; OR:0.27), fatigue during the day (very often vs. never/very rarely; OR:2.55), and headaches (no vs. yes; OR:0.44). In men, the following factors of urine osmolality were identified in 1st tertile: place of residence (city vs. village; OR:2.72) and health assessment (average vs. poor; OR:0.32).

CONCLUSION

Different factors affecting urine osmolality have been identified in women and men. These results highlight the need to implement studies to clarify the relationship between socioeconomic, lifestyle and health factors, and hydration status in adults with metabolic disorders.

Interindividual variability in appetitive sensations and relationships between appetitive sensations and energy intake

BACKGROUND

Appetitive sensations (AS) are signals that guide eating behaviors. Marked short-term inter-individual variability in AS has been reported but the long-term stability of individual ratings and their dietary implications are not well characterized.

OBJECTIVES

This study explored the stability of inter-individual ratings of hunger, fullness and thirst for 17 weeks; determined the relationships between these sensations, eating patterns and energy intake (EI); as well as the associations between ratings and selected individual characteristics (age, gender, BMI).

METHODS

A 17-week observational study collected hourly appetitive ratings and dietary intake data from 97 (90 completers, 7 partial completers) healthy adults at weeks 1, 9, and 17.

RESULTS

There were marked and stable inter-individual differences over the 17 weeks for hunger (week 1 vs. week 9, r = 0.72 (p < 0.001); week 1 vs. week 17, r = 0.67 (p < 0.001); week 9 vs. week 17, r = 0.77 (p < 0.001)); fullness (week 1 vs. week 9 r = 0.74 (p < 0.001); week 1 vs. week 17, r = 0.71 (p < 0.001); week 9 vs. week 17, r = 0.81 (p < 0.001)); and thirst (week 1 vs. week 9 r = 0.82 (p < 0.001); week 1 vs. week 17, r = 0.81 (p < 0.001); week 9 vs. week 17, r = 0.88 (p < 0.001)). Cross-correlation functions revealed EI and eating pattern exerted stronger effects on AS than the reverse. However, the absolute effect sizes were small. Path analyses also indicated that there were weak relationships between AS and EI. No robust effects of the studied individual characteristics were observed.

CONCLUSION

This study found that acute and chronic sensations of hunger, fullness and thirst are relatively stable within individuals but vary markedly between individuals. In addition, the present data indicate AS are poorly associated with dietary patterns or with EI under conditions of relatively stable energy balance.

Ionized alkaline water reduces injury in BALB/c mice infected with Leishmania amazonensis

Ionized water has been reported to contribute to the tissue repair process and wound healing. Water purifiers can generate ionized water by means of activated charcoal with silver and minerals, the main purpose of which are to reduce microbiological and physicochemical contaminants. Moreover, when water is subjected to a magnetic field an organization of water molecules occurs due to the presence of mineral salts. The resulting water is thus more alkaline, which has been shown to be non-toxic to mice and can actually prolong survival. Cutaneous leishmaniasis is a neglected tropical disease, caused by obligate uni- and intracellular protozoa belonging to the genus Leishmania, that can manifest in the form of skin lesions. Thus, the objective of this study was to compare the evolution of disease in L. amazonensis-infected BALB/c mice that received tap water (TW) or ionized alkaline water (IAW). As a control, additional groups of mice receiving TW or IAW were also treated with the antileishmanial miltefosine. All mouse groups received either TW or IAW as drinking water 30 days prior to infection and the groups continued to receive the respective drinking water for 4 weeks, after which the blood and plasma were collected. Biochemical assays of aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transferase, creatinine, urea, glucose, triglycerides, and cholesterol were performed, in addition to hematology tests. There was a significant decrease in the volume of the lesion for groups that received IAW, in which the ingestion of ionized alkaline water favored the non-evolution of the lesion in the footpads of the animals. The results of the blood count and leukogram tests were within the normal values for BALB/c mice demonstrating that ionized water has no toxic effects on blood factors.

Inhibition of salty taste and sodium appetite by estrogens in spontaneously hypertensive rats

Estrogen has a well-known effect of reducing salt intake in rats. This mini review focuses on recent findings regarding the interaction of estradiol with brain angiotensin II to control increased sodium palatability that occurs as a result of sodium appetite in spontaneously hypertensive rats.

Heat stress associated with aerosol PPE and its impact

BACKGROUND

Aerosol personal protective equipment (PPE) is subjectively reported to negatively impact healthcare workers' performance and well-being, but this has not been assessed objectively.

AIMS

This randomized controlled crossover study aimed to quantify the heat stress associated with aerosol PPE and to investigate its impact upon mood, cognitive and motor function, and task performance.

METHODS

Sixteen healthy, young, lean participants (eight males) undertook an exercise protocol, which simulated the metabolic expenditure of hospital work: once wearing aerosol PPE (PPE visit) and once wearing standard surgical attire (control visit). Participants walked on a treadmill for 2 h followed by 30-min rest. Core temperature, heart rate, urine specific gravity, weight, grip strength, mood (Bond-Lader scale) and task performance (Intubation of a Manikin) were recorded. Values are between-visit mean (standard deviation) differences.

RESULTS

On the PPE visit core temperature (+0.2 (0.3)°C; P < 0.01), heart rate (+12 (13) bpm; P < 0.001), urine specific gravity (+0.003 (0.005); P < 0.05) and intubation task time (+50 (81) s; P < 0.01) were greater than on the control visit; and alertness (-14 (21) mm; P < 0.001), contentment (-14 (15) mm; P < 0.001) and grip strength (-4 (4) N; P < 0.01) were less.

CONCLUSIONS

This study demonstrates that wearing aerosol PPE in a simulated hospital environment results in heat exhaustion and has a negative impact upon mood, motor function, and task performance. Whilst wearing PPE is important to prevent disease transmission, strategies should be developed to limit its impact upon healthcare workers' performance and well-being.

Human thirst behavior requires transformation of sensory inputs by intrinsic brain networks

BACKGROUND

To survive and thrive, many animals, including humans, have evolved goal-directed behaviors that can respond to specific physiological needs. An example is thirst, where the physiological need to maintain water balance drives the behavioral basic instinct to drink. Determining the neural basis of such behaviors, including thirst response, can provide insights into the way brain-wide systems transform sensory inputs into behavioral outputs. However, the neural basis underlying this spontaneous behavior remains unclear. Here, we provide a model of the neural basis of human thirst behavior.

RESULTS

We used fMRI, coupled with functional connectivity analysis and serial-multiple mediation analysis, we found that the physiological need for water is first detected by the median preoptic nucleus (MnPO), which then regulates the intention of drinking via serial large-scale spontaneous thought-related intrinsic network interactions that include the default mode network, salience network, and frontal-parietal control network.

CONCLUSIONS

Our study demonstrates that the transformation in humans of sensory inputs for a single physiological need, such as to maintain water balance, requires large-scale intrinsic brain networks to transform this input into a spontaneous human behavioral response.

An accurate wearable hydration sensor: Real-world evaluation of practical use

A wearable body hydration sensor employing photoplethysmographic and galvanic biosensors was field evaluated using 240 human participants with equal numbers of men and women volunteers. Monitoring of water mass loss due to perspiration was performed by medical balance measurements following one of two different treadmill physical exercise regimens over 90 minutes in 15-minute intervals with intervening 10-minute rest periods. Participants wore two different models of the dehydration body monitor device mated to commercially-available smartwatches (Samsung Gear S2 and Samsung Gear Fit2). Device output was recorded by Bluetooth wireless link to a standard smartphone in 20-second blocks. Comparison of the devices with the standard measurement method (change in body mass measured by medical balance) indicated very close agreement between changes in body water mass and device output (percent normalized mean root square error averaged approximately 2% for all participants). Bland-Altman analyses of method agreement indicated that <5% of participant values fell outside of the 95% confidence interval limits of agreement and all measured value differences were normally distributed around the line of equality. The results of this first-ever field trial of a practical, wearable hydration monitor suggests that this device will be a reliable tool to aid in geriatric hydration monitoring and physical training scenarios.

Fluid Balance and Carbohydrate Intake of Elite Female Soccer Players during Training and Competition

This study examined sweat rate, sweat sodium concentration [Na⁺], and ad-libitum carbohydrate and fluid intakes in elite female soccer players during training (n = 19) and a match (n = 8); eight completed both for comparisons. Body mass (kg) was obtained before and after exercise to calculate sweat rate. The sweat [Na⁺] was determined from absorbent patches on the thigh or back. Sweat rate, percentage body mass change, and sweat [Na⁺] for 19 players during training were 0.47 ± 0.19 L·h⁻¹, +0.19 ± 0.65%, and 28 ± 10 mmol·L⁻¹, respectively. Sweat rate was higher during a match (0.98 ± 0.34 L·h⁻¹) versus training (0.49 ± 0.26 L·h⁻¹, p = 0.007). Body mass losses were greater post-match (−1.12 ± 0.86%) than training (+0.29 ± 0.34%, p = 0.003). Sweat [Na⁺] was similar for training (29 ± 9 mmol·L⁻¹) and a match (35 ± 9 mmol·L⁻¹) (p = 0.215). There were no differences in match versus training carbohydrate intakes (2.0 ± 2.3 g·h⁻¹, 0.9 ± 1.5 g·h⁻¹, respectively, p = 0.219) or fluid intakes (0.71 ± 0.30 L·h⁻¹, 0.53 ± 0.21 L·h⁻¹, respectively, p = 0.114). In conclusion, female soccer players’ sweat rates were higher during a match than during training, and carbohydrate intakes were below recommendations for matches and training.

Cross-cultural variation in thirst perception in hot-humid and hot-arid environments: Evidence from two small-scale populations

OBJECTIVES

Thirst is an evolved central homeostatic feedback system that helps regulate body water for survival. Little research has examined how early development and exposure to extreme environments and water availability affect thirst perception, particularly outside Western settings. Therefore, we compared two indicators of perceived thirst (current thirst and pleasantness of drinking water) using visual scales among Tsimane' forager-horticulturalists in the hot-humid Bolivian Amazon and Daasanach agro-pastoralists in hot-arid Northern Kenya.

METHODS

We examined how these measures of perceived thirst were associated with hydration status (urine specific gravity), ambient temperatures, birth season, age, and population-specific characteristics for 607 adults (n = 378 Tsimane', n = 229 Daasanach) aged 18+ using multi-level mixed-effect regressions.

RESULTS

Tsimane' had higher perceived thirst than Daasanach. Across populations, hydration status was unrelated to both measures of thirst. There was a significant interaction between birth season and temperature on pleasantness of drinking water, driven by Kenya data. Daasanach born in the wet season (in utero during less water availability) had blunted pleasantness of drinking water at higher temperatures compared to those born in the dry season (in utero during greater water availability).

CONCLUSIONS

Our findings suggest hydration status is not a reliable predictor of thirst perceptions in extreme-hot environments with ad libitum drinking. Rather, our findings, which require additional confirmation, point to the importance of water availability during gestation in affecting thirst sensitivity to heat and water feedback mechanisms, particularly in arid environments. Thirst regulation will be increasingly important to understand given climate change driven exposures to extreme heat and water insecurity.

Predictive Validity of Image-Based Motivation-to-Eat Visual Analogue Scales in Normal Weight Children and Adolescents Aged 9-14 Years

Paper-based motivation-to-eat visual analogue scales (VASs) developed for adults are widely used in the pediatric age range. The VAS is comprised of four domains: hunger, fullness, desire to eat, and prospective food consumption. The purpose of the present study was to determine agreement between the traditional paper-based VAS and a novel digital VAS (with and without images), as well as the novel digital VAS's predictive validity for subsequent food intake (FI) in 9-14-year-old children and adolescents. Following an overnight fast and 3 h after consuming a standardized breakfast at home, children and adolescents (n = 17) completed three different VAS instruments (VAS_paper, VAS_images, VAS_no-images) in a randomized order at five time-points: 0 min (baseline), 5 min (immediately after consuming a 147 kcal yogurt treatment), 20 min, 35 min (immediately before an ad libitum lunch), and 65 min (immediately post ad libitum lunch). All three instruments were comparable, as shown by low bias and limits of agreement on Bland-Altman plots, moderate to excellent intraclass correlation coefficients for all domains at all time-points (ICC = 0.72-0.98), and no differences between the incremental area under the curve for any of the domains. All three instruments also showed good predictive validity for subsequent FI, with the strongest relationship observed immediately before the ad libitum lunch (p = 0.56-0.63). There was no significant association between subjective thirst and water intake, except with VAS_no-images at baseline (r = 0.49, p = 0.046). In conclusion, the present study suggests that a novel image-based digital VAS evaluating motivation-to-eat is interchangeable with the traditional paper-based VAS, and provides good predictive validity for next-meal FI in 9-14-year-old normal weight children and adolescents.

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.

"I know it's just pouring it from the tap, but it's not easy": Motivational processes that underlie water drinking

Water drinking behaviour is under-researched despite the prevalence and adverse health consequences of underhydration. We conducted a qualitative exploration into the motivational processes underlying water drinking, informed by a grounded cognition perspective on desire and motivated behaviour. We interviewed and analysed data from 60 participants stratified by age, gender, and education level using thematic analysis, to generate three key themes. "Water as situated habits," suggests that participants form and maintain situated water drinking habits, so that within certain situations they regularly drink water. However, participants who situated their water intake only in one key situation (e.g., work routine), had low and inconsistent intake when they left this situation. Some situations happened so infrequently during the day (e.g., before bed) that participants' daily water intake was low. Many participants reported drinking water in reaction to thirst cues, but these were easily suppressed or ignored, so that water drinking was inconsistent. Participants who saw drinking water as part of their self-identity had consistent and high water intake across a variety of situations. "Knowledge and attitudes," suggests that few participants had knowledge or attitudes that promoted water intake (e.g., perceived water as positive or understood the importance of hydration). "Strategies underlying attempts to increase intake" suggests that many participants lacked insight into strategies to increase water intake, although they spontaneously discussed attempts to drink more. This lead to ineffective attempts at behaviour change. Participants' mentions of dehydration and their responses to a urine colour chart suggested that many participants were possibly underhydrated. Our findings suggest that interventions and practitioners attempting to increase water intake need to increase knowledge about the importance of hydration, and encourage individuals to develop effective situated water drinking habits.

Evidence that variations in pre-training hydration status are related to the frequency of endurance training in elite adolescent sprinters

BACKGROUND

Although the effect of dehydration on performance is widely studied, limited data concerning the levels of risk training types pose to hydration status exists. This study sought to determine: (a) pre-training hydration status in adolescent sprinters relative to non-athletes, (b) changes in hydration markers across a season of adolescent sprinters relative to non-athletes, and (c) if frequency of training type explains unique variance in hydration.

METHODS

Hydration [via pre-training urine osmolality (UOsm) and thirst perception (TP)], daily water intake (TWI) [via 24-h food/fluid diaries] and frequencies of resistance, endurance and sprint training types (via training regime questionnaires) were assessed in 26 sprinters (age: 15.6±1.9 years) and 26 non-athletes (age: 16.0±1.6 years), during 4 mesocycles [general (T1) and specific (T2) preparation; pre-competitive (T3) and peaking (T4) phases], over 26 weeks.

RESULTS

Most athletes (62%-81%) and non-athletes (73%-92%) were underhydrated (UOsm>700 mOsmol/kg) pre-training across the season, despite a low TP. There were significant time (p =.042) and group (p =.006) effects, and a main group by time interaction for UOsm (p =.006) but not TP across the season, after controlling for TWI. Greater UOsm (in mOsmol/kg) were observed during T1 (906.3±250.1) and T2 (934.5±257.0) compared to T3 (852.1±268.8) and T4 (854.2±218.8). There was no significant change across the season for non-athletes. Frequencies of endurance training were positively associated with UOsm and explained unique variances across the season (R2 range from 7%-16%).

CONCLUSIONS

Underhydration is high in the adolescent population. Training type may be related to the variations in hydration throughout a season, which may help to inform hydration practices of sprint athletes.

Are older adults with excessive sodium intake at increased risk of hypohydration?

BACKGROUND

Sodium intake is expected to affect water needs, although compensation mechanisms may not work efficiently particularly in older adults. The aim of this cross-sectional study was to quantify the association between sodium excretion and hydration status in a representative sample of Portuguese older adults.

METHODS

A cluster sampling approach was used, representing Portuguese older adults (≥65 years) according to sex, education level and region. From a sample size of 1500 participants, 1318 were eligible for the present analysis. A 24-h urine sample was collected, and volume, osmolality, creatinine and sodium were quantified. Free water reserve (FWR) was used to assess hydration status. Excessive sodium intake was defined as above 2000 mg day^-1 as recommended by the World Health Organization. A multivariable binary logistic regression model was used to estimate the association between FWR and sodium excretion. Odds ratios (OR) and respective 95% confidence intervals (95% CI) were calculated.

RESULTS

Excessive sodium excretion was observed in 80.0% of women and 91.5% of men, whereas hypohydration affected 10.9% of women and 23.6% of men. After adjusting for confounders, excessive sodium excretion was associated with an increased risk of hypohydration among men (OR = 2.75; 95% CI = 1.06-7.15).

CONCLUSIONS

These results stress the positive association between excessive sodium intake and hypohydration in men and highlight the need for implementing strategies regarding the reduction of salt consumption and the promotion of water intake.

The sweat glands' maximum ion reabsorption rates following heat acclimation in healthy older adults

NEW FINDINGS

What is the central question to this study? Do the sweat glands' maximum ion reabsorption rates increase following heat acclimation in healthy older individuals and is this associated with elevated aldosterone concentrations? What is the main finding and its importance? Sweat gland maximum ion reabsorption rates improved heterogeneously across body sites, which occurred without any changes in aldosterone concentration following a controlled hyperthermic heat acclimation protocol in healthy older individuals.

ABSTRACT

We examined whether the eccrine sweat glands' ion reabsorption rates improved following heat acclimation (HA) in older individuals. Ten healthy older adults (>65 years) completed a controlled hyperthermic (+0.9°C rectal temperature, T_re ) HA protocol for nine non-consecutive days. Participants completed a passive heat stress test (lower leg 42°C water submersion) pre-HA and post-HA to assess physiological regulation of sweat gland ion reabsorption at the chest, forearm and thigh. The maximum ion reabsorption rate was defined as the inflection point in the slope of the relation between galvanic skin conductance and sweat rate (SR). We explored the responses again after a 7-day decay. During passive heating, the T_b thresholds for sweat onset on the chest and forearm were lowered after HA (P < 0.05). However, sweat sensitivity (i.e. the slope), the SR at a given T_re and gross sweat loss did not improve after HA (P > 0.05). Any changes observed were lost during the decay. Pilocarpine-induced sudomotor responses to iontophoresis did not change after HA (P ≥ 0.801). Maximum ion reabsorption rate was only enhanced at the chest (P = 0.001) despite unaltered aldosterone concentration after HA. The data suggest that this adaptation is lost after 7 days' decay. The HA protocol employed in the present study induced partial adaptive sudomotor responses. Eccrine sweat gland ion reabsorption rates improved heterogeneously across the skin sites. It is likely that aldosterone secretion did not alter the chest sweat ion reabsorption rates observed in the older adults.

Thirst as an ingestive behavior: A brief review on physiology and assessment

BACKGROUND

Thirst is a sensation normally aroused by a lack of water and associated with a desire to drink more fluid.

AIM

The aims of this brief review are twofold: (a) to summarize the thirst mechanism in how it is initiated and diminished, and (b) to describe techniques to assess human thirst accurately in a variety of situations.

DISCUSSION

Thirst is maintained via a feedback-controlled mechanism, regulated by central and peripheral factors, as well as social and psychological cues. Most studies of thirst have focused on the initiation of water intake and the neural mechanisms responsible for this vital behavior. Less attention has been paid to the stimuli and mechanisms that terminate a bout of drinking and limit fluid ingestion, such as oropharyngeal and gastric signals, coupled with osmotic sensations. Thirst perception is typically assessed by subjective ratings using a variety of questionnaires, rankings, or visual analog scales. However, the appropriate perceptual tool may not always be used for the correct assessment of thirst perception.

CONCLUSIONS

In considering the many factors involved in thirst arousal and inhibition, similar questions need to be considered for the correct assessment of this ingestive behavior.

Changes of Hydration Measures in Elite National Collegiate Athletic Association Division I Wrestlers

PURPOSE

To evaluate the changes in the state of hydration in elite National Collegiate Athletic Association (NCAA) Division I college wrestlers during and after a season.

METHODS

Ohio State University wrestling team members (N = 6; mean [SD] age = 19.6 [1.1] y; height = 171.6 [2.9] cm; body mass = 69.5 [8.1] kg) gave informed consent to participate in the investigation with measurements (ie, body mass, urine-specific gravity [USG; 2 methods], Visual Analog Scale thirst scale, plasma osmolality) obtained during and after the season.

RESULTS

Measurements for USG, regardless of methods, were not significantly different between visits, but plasma osmolality was significantly (P = .001) higher at the beginning of the season-295.5 (4.9) mOsm·kg-1 compared with 279.6 (6.1) mOsm·kg-1 after the season. No changes in thirst ratings were observed, and the 2 measures of USG were highly correlated (r > .9, P = .000) at each time point, but USG and plasma osmolality were not related.

CONCLUSIONS

A paradox in the clinical interpretation of euhydration in the beginning of the season was observed with the USG, indicating that the wrestlers were properly hydrated, while the plasma osmolality showed they were not. Thus, the tracking of hydration status during the season is a concern when using only NCAA policies and procedures. The wrestlers did return to normal euhydration levels after the season on both biomarkers, which is remarkable, as previous studies have indicated that this may not happen because of the reregulation of the osmol-regulatory center in the brain.

Possible Biological Mechanisms Linking Mental Health and Heat-A Contemplative Review

This review provides examples of possible biological mechanisms that could, at least partly, explain the existing epidemiological evidence of heatwave-related exacerbation of mental disease morbidity. The author reviews the complicated central processes involved in the challenge of maintaining a stable body temperature in hot environments, and the maladaptive effects of certain psychiatric medicines on thermoregulation. In addition, the author discusses some alternative mechanisms, such as interrupted functional brain connectivity and the effect of disrupted sleep, which may further increase the vulnerability of mental health patients during heatwaves.

Mobile Technology Application for Improved Urine Concentration Measurement Pilot Study

Objectives: Low hydration has a deleterious effect on many conditions. In the absence of a urine concentrating defect, urine concentration is a marker of hydration status. However, markers to evaluate hydration status have not been well studied in children. The objectives of this paper are to compare measures of thirst and urine concentration in children and to develop a novel mobile technology application to measure urine concentration. Study Design: Children age 12-17 years were selected (n = 21) for this pilot study. Thirst perception, specific gravity (automated dipstick analysis and refractometer), and urine color scale results were correlated to urine osmolality. The technology department developed a mobile technology camera application to measure light penetrance into urine which was tested on 25 random anonymized urine samples. Results: The patients' thirst perception and color scale as well as two researchers color scale did not significantly correlate with osmolality. Correlation between osmolality and hydration markers resulted in the following Pearson coefficients: SG automated dipstick, 0.61 (P 0.003); SG refractometer, 0.98 (P < 0.0001); urine color scale (patient), 0.37 (P 0.10), and light penetrance, -0.77 (P < 0.0001). The correlation of light penetrance with osmolality was stronger than all measures except SG by refractometer and osmolality. Conclusion: The mobile technology application may be a more accurate tool for urine concentration measurement than specific gravity by automated dipstick, subjective thirst, and urine color scale, but lags behind specific gravity measured by refractometer. The mobile technology application is a step toward patient oriented hydration strategies.

Engineering Approaches to Assessing Hydration Status

Dehydration is a common condition characterized by a decrease in total body water. Acute dehydration can cause physical and cognitive impairment, heat stroke and exhaustion, and, if severe and uncorrected, even death. The health effects of chronic mild dehydration are less well studied with urolithiasis (kidney stones) the only condition consistently associated with it. Aside from infants and those with particular medical conditions, athletes, military personnel, manual workers, and older adults are at particular risk of dehydration due to their physical activity, environmental exposure, and/or challenges in maintaining fluid homeostasis. This review describes the different approaches that have been explored for hydration assessment in adults. These include clinical indicators perceived by the patient or detected by a practitioner and routine laboratory analyses of blood and urine. These techniques have variable accuracy and practicality outside of controlled environments, creating a need for simple, portable, and rapid hydration monitoring devices. We review the wide array of devices proposed for hydration assessment based on optical, electromagnetic, chemical, and acoustical properties of tissue and bodily fluids. However, none of these approaches has yet emerged as a reliable indicator in diverse populations across various settings, motivating efforts to develop new methods of hydration assessment.

Incidence and physiological mechanism of carboplatin-induced electrolyte abnormality among patients with non-small cell lung cancer

To clarify the association between carboplatin and electrolyte abnormality, a pooled-analysis was performed with the adverse event reports of non-small cell lung cancer patients. A total of 19901 adverse events were retrieved from the FDA Adverse Event Reporting System (FAERS). Pooled reporting odds ratios (RORs) and 95% CIs suggested that carboplatin was significantly associated with hyponatremia (pooled ROR = 1.57, 95% CI 1.18-2.09, P = 1.99×10-3) and hypokalemia (pooled ROR = 2.37, 95% CI 1.80-3.10, P = 5.24×10-10) as compared to other therapies. In addition, we found that dehydration was frequently concurrent with carboplatin therapy (pooled ROR = 2.01, 95% CI 1.52-2.66, P = 8.37×10-7), which may prompt excessive water ingestion and decrease serum electrolyte concentrations. This information has not been mentioned in the FDA-approved drug label and could help explain the physiological mechanism of carboplatin-induced electrolyte abnormality. In conclusion, the above results will facilitate clinical management and prompt intervention of life-threatening electrolyte imbalance in the course of cancer treatment.

Developing and validating the Perioperative Thirst Discomfort Scale

Abstract OBJECTIVE Developing and validating a scale to assess perioperative thirst discomfort. METHOD A methodological research conducted in 2014 and 2015 at the surgical center of a public hospital in the north of Paraná, Brazil. The scale was developed after literature review, followed by face and content validation, and reliability assessment through its internal consistency and inter-observer equivalence. RESULTS Seven items make up the scale: dry mouth; dry lips; thick tongue; thick saliva; dry throat, bad taste and desire to drink water. The content validity index for attributes and items was 0.98, and the reliability index was 1 for the scale attributes and items. Internal consistency assessed by Cronbach's alpha was 0.91 and inter-rater equivalence was 1, as measured by weighted kappa coefficient. CONCLUSION ThePerioperative Thirst Discomfort Scaleshowed high content and reliability indexes.

Limitations to Thermoregulation and Acclimatization Challenge Human Adaptation to Global Warming

Human thermoregulation and acclimatization are core components of the human coping mechanism for withstanding variations in environmental heat exposure. Amidst growing recognition that curtailing global warming to less than two degrees is becoming increasing improbable, human survival will require increasing reliance on these mechanisms. The projected several fold increase in extreme heat events suggests we need to recalibrate health protection policies and ratchet up adaptation efforts. Climate researchers, epidemiologists, and policy makers engaged in climate change adaptation and health protection are not commonly drawn from heat physiology backgrounds. Injecting a scholarly consideration of physiological limitations to human heat tolerance into the adaptation and policy literature allows for a broader understanding of heat health risks to support effective human adaptation and adaptation planning. This paper details the physiological and external environmental factors that determine human thermoregulation and acclimatization. We present a model to illustrate the interrelationship between elements that modulate the physiological process of thermoregulation. Limitations inherent in these processes, and the constraints imposed by differing exposure levels, and thermal comfort seeking on achieving acclimatization, are then described. Combined, these limitations will restrict the likely contribution that acclimatization can play in future human adaptation to global warming. We postulate that behavioral and technological adaptations will need to become the dominant means for human individual and societal adaptations as global warming progresses.

Sensory attributes of soft drinks and their influence on consumers' preferences

Soft drinks are beverages composed of water and other ingredients that provide specific sensorial attributes. Soft drink consumption patterns have recently been changed partially influenced by an increased availability of different types of beverages during the last few years. Consumers' preferences to choose one drink over another are influenced, not only by genetic, psychological and environmental factors, but also by the beverage's specific attributes. In fact, beverage consumption is driven by the sensations it gives. Because the main component of soft drinks is water, an increase in the intake of soft drinks might improve fluid intake and the levels of water in the body if it is regarded as an "essential nutrient".

Validation analysis of a geriatric dehydration screening tool in community-dwelling and institutionalized elderly people

Dehydration is common among elderly people. The aim of this study was to perform validation analysis of a geriatric dehydration-screening tool (DST) in the assessment of hydration status in elderly people. This tool was based on the DST proposed by Vivanti et al., which is composed by 11 items (four physical signs of dehydration and seven questions about thirst sensation, pain and mobility), with four questions extra about drinking habits. The resulting questionnaire was evaluated in a convenience sample comprising institutionalized (n = 29) and community-dwelling (n = 74) elderly people. Urinary parameters were assessed (24-h urine osmolality and volume) and free water reserve (FWR) was calculated. Exploratory factor analysis was used to evaluate the scale’s dimensionality and Cronbach’s alpha was used to measure the reliability of each subscale. Construct’s validity was tested using linear regression to estimate the association between scores in each dimension and urinary parameters. Two factors emerged from factor analysis, which were named “Hydration Score” and “Pain Score”, and both subscales showed acceptable reliabilities. The “Hydration Score” was negatively associated with 24-h urine osmolality in community-dwelling; and the “Pain Score” was negatively associated with 24-h urine osmolality, and positively associated with 24-h urine volume and FWR in institutionalized elderly people.

Opportunities for intervention strategies for weight management: global actions on fluid intake patterns

Water is an essential nutrient for all physiological functions and particularly important for thermoregulation. About 60% of our body weight is made of water. Under standard conditions (18-20 °C and moderate activity), water balance is regulated within 0.2 % of body weight over a 24-hour period. Water requirement varies between individuals and according to environmental conditions. Concerning considerations related to obesity, the health impact of fluid intake is commonly overlooked. Fluid intake advices are missing in most of food pyramids offered to the public, and water requirements and hydration challenges remain often neglected. The purpose of this paper is to emphasize and discuss the role of water consumption in the context of other important public health measures for weight management. Attention will be focused on fluid intake patterns and hydration-related questions in the context of global interventions and/or physical activity programs settled in weight management protocols.

Does salt increase thirst?

Our diet is believed to be overly rich in sodium, and it is commonly believed that sodium intake increases drinking. Hence the concern of a possible contribution of dietary sodium to beverage intake which in turn may contribute to obesity and ill health. Here we examine whether voluntary, acute intake of a sodium load, as occurs in routine eating and snacking, increases thirst and drinking. We find that after ingesting 3.5 or 4.4 g NaCl (men) and 1.9 or 3.7 g (women) on nuts during 15 minutes, there is no increase in thirst or drinking of freely available water in the following 2 h compared with eating similar amounts of sugared or unflavored nuts. This suggests that routine ingestion of boluses of salt (~30-40% of daily intake for men, ~ 20-40% for women) does not increase drinking. Methodological concerns such as about nuts as vehicle for sodium suggest further research to establish the generalizability of this unexpected result.

Qualitative and/or quantitative drinking water recommendations for pediatric obesity treatment

OBJECTIVE

The qualitative recommendation to 'drink water instead of caloric beverages' may facilitate pediatric obesity treatment by lowering total energy intake. The quantitative recommendation to 'drink enough water to dilute urine' might further facilitate weight loss by increasing fat oxidation via cell hydration-mediated changes in insulin.

METHODS

This 8 week randomized intervention tested whether both qualitative-plus-quantitative (QQ) drinking water recommendations result in more weight loss than the qualitative recommendation alone (Q) in 25 children (9-12y) with body mass index at or above the 85th Percentile, given a reduced glycemic diet and usual physical activity. Random urine osmolality, saliva insulin, and body weight were assessed weekly. Mixed models explored if insulin mediated an effect of urine osmolality on weight loss.

RESULTS

In intention-to-treat analyses, QQ and Q participants did not differ significantly with respect to level of urine osmolality, saliva insulin, or weight loss. Only 4 out of 16 QQ participants complied with instruction to drink enough water to dilute urine, however. In completers analyses, the compliant QQ participants, who diluted urine osmolality from 910 ± 161 mmol/kg at baseline to below 500 mmol/kg over time (8 week mean±SE: 450 ± 67 mmol/kg), had significantly lower saliva insulin over time (8 week mean±SE: 13 ± 8 pmol/l vs. 22 ± 4 pmol/l) and greater weight loss (mean ± SE: -3.3 ± 0.7kg vs. -2.0 ± 0.5 kg) than compliant Q participants (7 out of 9 participants) who maintained elevated urine osmolality over time (8- week mean±SE: 888 ± 41 mmol/kg). Urine osmolality below 500 mmol/kg was significantly associated with weight loss. Change in saliva insulin partially explained the association.

CONCLUSIONS

QQ recommendations may increase weight loss for those able to dilute urine. Work is warranted to pursue cell hydration effects of drinking water for pediatric obesity treatment.

Drinking to thirst versus drinking ad libitum during road cycling

CONTEXT

The sensation of thirst is different from the complex behavior of drinking ad libitum. Rehydration recommendations to athletes differ, depending on the source, yet no previous researchers have systematically compared drinking to thirst (D(TT)) versus ad libitum drinking behavior (D(AL)).

OBJECTIVE

To compare 2 groups of trained cyclists (D(TT) and D(AL)) who had similar physical characteristics and training programs (P > .05). The D(TT) group (n = 12, age = 47 ± 7 years) drank only when thirsty, whereas the D(AL) group (n = 12, age = 44 ± 7 years) consumed fluid ad libitum (ie, whenever and in whatever volume desired).

DESIGN

Cohort study.

SETTING

Road cycling (164 km) in the heat (36.1 °C ± 6.5 °C).

PATIENTS OR OTHER PARTICIPANTS

Ultraendurance cyclists (4 women, 20 men).

INTERVENTION(S)

We recorded measurements 1 day before the event, on event day before the start, at 3 roadside aid stations, at the finish line, and 1 day after the event.

MAIN OUTCOME MEASURE(S)

Body mass, urinary hydration indices, and food and fluids consumed.

RESULTS

No between-groups differences were seen on event day for total exercise time (DTT = 6.69 ± 0.89 hours, DAL = 6.66 ± 0.77 hours), urinary indices (specific gravity, color), body mass change (D(TT) = -2.22% ± 1.73%, DAL = -2.29% ± 1.62%), fluid intake (D(TT) = 5.63 ± 2.59 L/6.7 h, D(AL) = 6.04 ± 2.37 L/6.7 h), dietary energy intake, macronutrient intake, ratings of thirst (D(TT) start = 2 ± 1, D(TT) finish = 6 ± 1, DAL start = 2 ± 1, D(AL) finish = 6 ± 1), pain, perceived exertion, or thermal sensation. Total fluid intake on recovery day +1 was the primary significant difference (D(AL) = 5.13 ± 1.87 L/24 h, D(TT) = 3.13 ± 1.53 L/24 h, t18 = 2.59, P = .02).

CONCLUSIONS

Observations on event day indicated that drinking to thirst and drinking ad libitum resulted in similar physiologic and perceptual outcomes. This suggests that specific instructions to "drink to thirst" were unnecessary. Indeed, if athletes drink ad libitum, they can focus on training and competition rather than being distracted by ongoing evaluation of thirst sensations.