Underhydration Is Associated with Obesity, Chronic Diseases, and Death Within 3 to 6 Years in the U.S. Population Aged 51-70 Years

Impact of mask wearing time on fluid consumption and physical activity during the COVID-19 pandemic

Purpose

To examine the associations between mask-wearing on fluid consumption and physical activity behaviors during the COVID-19 pandemic.

Methods

137 college students (female, 72.5%; age, 26 ± 9 y) completed a survey detailing their fluid intake, physical activity behaviors, and time spent wearing a mask throughout the day during the previous month in the Fall 2020 academic semester.

Results

Increased daily mask wearing time was not associated with total fluid intake (p > 0.05). Participants had greater odds of being 'somewhat active' compared to 'inactive' with an increase in mask wearing time (OR = 1.23 [1.03, 1.47], p = 0.022).

Conclusion

Wearing a mask during the COVID-19 pandemic did not influence fluid intake behaviors, however, it increased the likelihood of reported greater levels of physical activity. These factors may be related to an individual being more likely to globally adopt healthier behaviors, however, this needs further exploration.

Habitual water intake impacted the body composition of young male athletes in free-living conditions: a cross-sectional study

The study aimed to explore the associations between water intake and body composition and differences of body composition in different water itake and hydration statuses among young male athletes. A cross-sectional study was conducted among 111 young male athletes in Beijing, China. Total drinking fluids (TDF) and water from food were assessed using a 7-day, 24-h fluid intake record questionnaire and the duplicate portion method, respectively. The osmolality of 24-hour urine and blood samples was tested. Body composition was measured using a bioelectrical impedance analyzer twice at 5-min intervals. Participants were divided into two groups based on the recommendations of total water intake (TWI) and TDF in China, as well as into three groups based on 24-h urine osmolality. Pearson's correlation coefficients were calculated to determine the relationship between water intake and body composition. Chi-square tests and Student's t-tests were used to compare differences. A total of 109 participants completed the study. TDF (r = 0.230, p = 0.016; r = 0.234, p = 0.014; r = 0.242, p = 0.011) and TWI (r = 0.275, p = 0.004; r = 0.243, p = 0.011; r = 0.243, p = 0.011) were positively correlated with total body water (TBW), intracellular water (ICW), and extracellular water (ECW). TBW/body weight (BW) was positively associated with TDF percentage of BW (TDF/BW) (r = 0.267, p = 0.005), water from food percentage of BW (r = 0.217, p = 0.024), and TWI percentage of BW (TWI/BW) (r = 0.316, p = 0.001). Participants who met the TDF recommendation of China had 1.3 kg higher skeletal muscle mass (SMM), 0.9 kg higher ICW, and 0.5% higher TBW/BW than those who did not (all p < 0.05), with fat-free mass (FFM) and TBW being higher (p = 0.051; p = 0.050). Those who met the TWI recommendation of China had 1.3 kg higher SMM, 2.4 kg higher FFM, 1.1 kg higher ICW, 0.6 kg higher ECW, and 1.7 kg higher TBW than their counterparts (all p < 0.05). Moderate associations were found between water intake and body composition. No significant differences were observed among participants in three hydration statuses (all p > 0.05). Participants who met the TWI or TDF recommendations had better body composition distribution than their counterparts. Thus, habitual water intake, not hydration status, affects body composition among athletes in free-living conditions.

Low daily water intake profile-is it a contributor to disease?

Few previous review articles have focused on the associations between inadequate daily water intake (LOW) or urinary biomarkers of dehydration (UD; low urine volume or high urine osmolality) and multiple diseases. Accordingly, we conducted manual online searches (47 key words) of the PubMed, Embase, and Google Scholar databases with these inclusion criteria: English language, full-text, peer reviewed, no restriction on research design, and three publications minimum. Initially, 3,903 articles were identified based on their titles and abstracts. Evaluations of full length .pdf versions identified 96 studies that were acceptable for inclusion. We concluded that the evidence is insufficient or conflicting for seven disorders or diseases (i.e. suggesting the need for additional clarifying research) and it is lacking for all-cause mortality. Differential characterizations among women and men have been reported in the results of nine studies involving five diseases. Finally, the evidence for associations of LOW or UD is strong for both kidney stones and type 2 diabetes with hyperglycemia. This suggests that great public health value (i.e. reduced disease risk) may result from increased daily water intake-a simple and cost-effective dietary modification.

Sleep, Health Outcomes and Body Weight (SHOW) study: a measurement burst design study on sleep and risk factors for obesity in black emerging adults in North Carolina, USA

INTRODUCTION

Black emerging adults (18-28 years) have the highest risk of short sleep duration and obesity. This increased risk may be partly explained by greater stress levels, which may result from race-related stress (racial discrimination and heightened race-related vigilance) or living in more disadvantaged home and neighbourhood environments. Insufficient sleep may also impact obesity risk via several weight-related mechanisms including energy balance, appetite and food reward, cortisol profiles and hydration status. This paper describes the rationale, design and methods for the Sleep, Health Outcomes and Body Weight (SHOW) study. This study aims to prospectively assess the effects of sleep, race-related stress and home/neighbourhood environments on weight-related mechanisms and obesity markers (body weight, waist circumference and fat mass) in 150 black emerging adults.

METHODS AND ANALYSIS

The SHOW study follows a measurement burst design that includes 3, 7-day data collection bursts (baseline, 6-month and 12-month follow-ups). Sleep is measured with three methods: sleep diary, actigraphy and polysomnography. Energy balance over 7 days is based on resting and postprandial energy expenditure measured via indirect calorimetry, physical activity via accelerometry and self-reported and ad libitum energy intake methods. Self-reported methods and blood biomarkers assess fasting and postprandial appetite profiles and a behavioural-choice task measures food reward. Cortisol awakening response and diurnal cortisol profiles over 3 days are assessed via saliva samples and chronic cortisol exposure via a hair sample. Hydration markers are assessed with 24-hour urine collection over 3 days and fasting blood biomarkers. Race-related stress is self-reported over 7 days. Home and neighbourhood environments (via the Windshield Survey) is observer assessed.

ETHICS AND DISSEMINATION

Ethics approval was granted by the University of North Carolina at Greensboro's Institutional Review Board. Study findings will be disseminated through peer-reviewed publications, presentations at scientific meetings and reports, briefs/infographics for lay and community audiences.

Sufficient water intake maintains the gut microbiota and immune homeostasis and promotes pathogen elimination

Water is the most abundant substance in the human body and plays a pivotal role in various bodily functions. While underhydration is associated with the incidence of certain diseases, the specific role of water in gut function remains largely unexplored. Here, we show that water restriction disrupts gut homeostasis, which is accompanied by a bloom of gut microbes and decreased numbers of immune cells, especially Th17 cells, within the colon. These microbial and immunological changes in the gut are associated with an impaired ability to eliminate the enteric pathogen Citrobacter rodentium. Moreover, aquaporin 3, a water channel protein, is required for the maintenance of Th17 cell function and differentiation. Taken together, adequate water intake is critical for maintaining bacterial and immunological homeostasis in the gut, thereby enhancing host defenses against enteric pathogens.

Ten tips on how to care for your CKD patients in episodes of extreme heat

Climate change is responsible for ≈75% of extreme heat events throughout the world. Heat events are associated with an increased risk for acute kidney injury, which contributes to the development of chronic kidney disease (CKD) and cardiovascular events. Patients with CKD are especially vulnerable to heat stress for a variety of reasons. A disproportionate percentage of patients with CKD live in poverty; experience homelessness, mental illness or disabilities; work outside or are elderly, all demographics that overlap with populations most susceptible to episodes of extreme heat. Therefore, it is reasonable to conclude that exposure to episodes of extreme heat can lead to the progression of CKD and increases morbidity and mortality. Given these concerns, clinicians must be prepared to promptly recognize complications of heat in CKD patients and to help patients appropriately acclimate. We propose the following tips for clinicians to effectively care for their CKD patients during extreme heat days.

Association between Urine Specific Gravity as a Measure of Hydration Status and Risk of Type 2 Diabetes: The Kailuan Prospective Cohort Study

Diabetes, especially type 2 diabetes (T2D), poses an unprecedented challenge to global public health. Hydration status also plays a fundamental role in human health, especially in people with T2D, which is often overlooked. This study aimed to explore the longitudinal associations between hydration status and the risk of T2D among the Chinese population. This study used data from the large community-based Kailuan cohort, which included adults who attended physical examinations from 2006 to 2007 and were followed until 2020. A total of 71,526 participants who eventually met the standards were divided into five hydration-status groups based on their levels of urine specific gravity (USG). Multivariable and time-dependent Cox proportional hazards models were employed to evaluate the associations of baseline and time-dependent hydration status with T2D incidence. Restricted cubic splines (RCS) analysis was used to examine the dose-response relationship between hydration status and the risk of T2D. Over a median 12.22-year follow-up time, 11,804 of the participants developed T2D. Compared with the optimal hydration-status group, participants with dehydration and severe dehydration had a significantly increased risk of diabetes, with adjusted hazard ratios (95% CI) of 1.30 (1.04-1.63) and 1.38 (1.10-1.74). Time-dependent analyses further confirmed the adverse effects of impending dehydration, dehydration, and severe dehydration on T2D incidence by 16%, 26%, and 33% compared with the reference group. Inadequate hydration is significantly associated with increased risks of T2D among Chinese adults. Our findings provided new epidemiological evidence and highlighted the potential role of adequate hydration status in the early prevention of T2D development.

Long-term health outcomes associated with hydration status

Body water balance is determined by fundamental homeostatic mechanisms that maintain stable volume, osmolality and the composition of extracellular and intracellular fluids. Water balance is maintained by multiple mechanisms that continuously match water losses through urine, the skin, the gastrointestinal tract and respiration with water gains achieved through drinking, eating and metabolic water production. Hydration status is determined by the state of the water balance. Underhydration occurs when a decrease in body water availability, due to high losses or low gains, stimulates adaptive responses within the water balance network that are aimed at decreasing losses and increasing gains. This stimulation is also accompanied by cardiovascular adjustments. Epidemiological and experimental studies have linked markers of low fluid intake and underhydration - such as increased plasma concentration of vasopressin and sodium, as well as elevated urine osmolality - with an increased risk of new-onset chronic diseases, accelerated aging and premature mortality, suggesting that persistent activation of adaptive responses may be detrimental to long-term health outcomes. The causative nature of these associations is currently being tested in interventional trials. Understanding of the physiological responses to underhydration may help to identify possible mechanisms that underlie potential adverse, long-term effects of underhydration and inform future research to develop preventative and treatment approaches to the optimization of hydration status.

Bioelectrical impedance vector analysis is different according to the comorbidity burden in post-acute myocardial infarction

BACKGROUND

The prevalence of a high comorbidity burden in patients who suffered an acute myocardial infarction (AMI) is increasing with the aging population, and the nutrition status also may be a predictor of clinical outcomes for these patients. This study aimed to investigate the relationship between the comorbidity burden and the characteristics of the bioelectrical impedance vector analysis (BIVA) in patients post-AMI.

METHODS

This prospective observational cohort study was conducted with adult patients who were hospitalized with AMI. Pre-existing comorbidities were assessed by the Charlson comorbidity index (CCI) adjusted by age, and anthropometric and BIVA characteristics were evaluated after the hemodynamic stabilization. All patients were followed-up until hospital discharge, and their length of stay was observed.

RESULTS

A total of 184 patients (75% were males; mean age, 60.2 ± 12.3 years) were included. The most common comorbidities were dyslipidemia (73.9%), hypertension (62%), and type 2 diabetes (34.2%). A higher CCI (≥3) was associated with sex (P = 0.008) and age (P < 0.001). Regarding BIVA, statistically significant differences were detected between sex (P < 0.001), age (P < 0.001), and CCI (P = 0.003), with longer vectors in female, older adults, and those with CCI ≥ 3.

CONCLUSION

Finding a relationship between BIVA and CCI suggests the first identified coherent differences, potentially correlated with diseases, representing a first contribution to support this type of assessment. Therefore, with BIVA, healthcare professionals may monitor abnormalities and adopt preventive nutrition care measures on patients post-AMI to improve their clinical status.

Hypohydration attenuates increases in creatinine clearance to oral protein loading and the renal hemodynamic response to exercise pressor reflex

Insufficient hydration is prevalent among free living adults. This study investigated whether hypohydration alters 1) renal functional reserve, 2) the renal hemodynamic response to the exercise pressor reflex, and 3) urine-concentrating ability during oral protein loading. In a block-randomized crossover design, 22 healthy young adults (11 females and 11 males) underwent 24-h fluid deprivation (Hypohydrated) or 24-h normal fluid consumption (Euhydrated). Renal functional reserve was assessed by oral protein loading. Renal hemodynamics during the exercise pressor reflex were assessed via Doppler ultrasound. Urine-concentrating ability was assessed via free water clearance. Creatinine clearance did not differ at 150 min postprotein consumption between conditions [Hypohydrated: 246 mL/min, 95% confidence interval (CI): 212-280; Euhydrated: 231 mL/min, 95% CI: 196-265, P = 0.2691] despite an elevated baseline in Hypohydrated (261 mL/min, 95% CI: 218-303 vs. 143 mL/min, 95% CI: 118-168, P < 0.0001). Renal artery vascular resistance was not different at baseline (P = 0.9290), but increases were attenuated in Hypohydrated versus Euhydrated at the end of handgrip (0.5 mmHg/cm/s, 95% CI: 0.4-0.7 vs. 0.8 mmHg/cm/s 95% CI: 0.6-1.1, P = 0.0203) and end occlusion (0.2 mmHg/cm/s, 95% CI: 0.1-0.3 vs. 0.4 mmHg/cm/s 95% CI: 0.3-0.6, P = 0.0127). There were no differences between conditions in free water clearance at 150 min postprotein (P = 0.3489). These data indicate that hypohydration 1) engages renal functional reserve and attenuates the ability to further increase creatinine clearance, 2) attenuates increases in renal artery vascular resistance to the exercise pressor reflex, and 3) does not further enhance nor impair urine-concentrating ability during oral protein loading.NEW & NOTEWORTHY Insufficient hydration is prevalent among free living adults. This study found that hypohydration induced by 24-h fluid deprivation engaged renal functional reserve and that oral protein loading did not further increase creatinine clearance. Hypohydration also attenuated the ability to increase renal vascular resistance during the exercise pressor reflex. In addition, hypohydration neither enhanced nor impaired urine-concentrating ability during oral protein loading. These data support the importance of mitigating hypohydration in free living adults.

The fructose survival hypothesis as a mechanism for unifying the various obesity hypotheses

The pathogenesis of obesity remains contested. Although genetics is important, the rapid rise in obesity with Western culture and diet suggests an environmental component. Today, some of the major hypotheses for obesity include the energy balance hypothesis, the carbohydrate-insulin model, the protein-leverage hypothesis, and the seed oil hypothesis. Each hypothesis has its own support, creating controversy over their respective roles in driving obesity. Here we propose that all hypotheses are largely correct and can be unified by another dietary hypothesis, the fructose survival hypothesis. Fructose is unique in resetting ATP levels to a lower level in the cell as a consequence of suppressing mitochondrial function, while blocking the replacement of ATP from fat. The low intracellular ATP levels result in carbohydrate-dependent hunger, impaired satiety (leptin resistance), and metabolic effects that result in the increased intake of energy-dense fats. This hypothesis emphasizes the unique role of carbohydrates in stimulating intake while fat provides the main source of energy. Thus, obesity is a disorder of energy metabolism, in which there is low usable energy (ATP) in the setting of elevated total energy. This leads to metabolic effects independent of excess energy while the excess energy drives weight gain.

Salty Subjects: Unpacking Racial Differences in Salt-Sensitive Hypertension

PURPOSE OF REVIEW

To review underlying mechanisms and environmental factors that may influence racial disparities in the development of salt-sensitive blood pressure.

RECENT FINDINGS

Our group and others have observed racial differences in diet and hydration, which may influence salt sensitivity. Dietary salt elicits negative alterations to the gut microbiota and immune system, which may increase hypertension risk, but little is known regarding potential racial differences in these physiological responses. Antioxidant supplementation and exercise offset vascular dysfunction following dietary salt, including in Black adults. Furthermore, recent work proposes the role of racial differences in exposure to social determinants of health, and differences in health behaviors that may influence risk of salt sensitivity. Physiological and environmental factors contribute to the mechanisms that manifest in racial differences in salt-sensitive blood pressure. Using this information, additional work is needed to develop strategies that can attenuate racial disparities in salt-sensitive blood pressure.

Effect of fluid replacement with green tea on body fluid balance and renal responses under mild thermal hypohydration: a randomized crossover study

PURPOSE

Maintaining an appropriate hydration level by ingesting fluid in a hot environment is a measure to prevent heat-related illness. Caffeine-containing beverages, including green tea (GT), have been avoided as inappropriate rehydration beverages to prevent heat-related illness because caffeine has been assumed to exert diuretic/natriuretic action. However, the influence of caffeine intake on urine output in dehydrated individuals is not well documented. The aim of the present study was to examine the effect of fluid replacement with GT on body fluid balance and renal water and electrolyte handling in mildly dehydrated individuals.

METHODS

Subjects were dehydrated by performing three bouts of stepping exercise for 20 min separated by 10 min of rest. They were asked to ingest an amount of water (H2O), GT, or caffeinated H2O (20 mg/100 ml; Caf-H2O) that was equal to the volume of fluid loss during the dehydration protocol; fluid balance was measured for 2 h after fluid ingestion.

RESULTS

The dehydration protocol induced hypohydration by ~ 10 g/kg body weight (~ 1% of body weight). Fluid balance 2 h after fluid ingestion was significantly less negative in all trials, and the fluid retention ratio was 52.2 ± 4.2% with H2O, 51.0 ± 5.0% with GT, and 47.9 ± 6.2% with Caf-H2O; those values did not differ among the trials. After rehydration, urine output, urine osmolality, and urinary excretions of osmotically active substances, sodium, potassium and chloride were not different among the trials.

CONCLUSION

The data indicate that ingestion of GT or an equivalent caffeine amount does not worsen the hydration level 2 h after ingestion and can be effective in reducing the negative fluid balance for acute recovery from mild hypohydration.

TRIAL REGISTRATION

ISRCTN53057185; retrospectively registered.

Cross-sectional analysis of racial differences in hydration and neighborhood deprivation in young adults

BACKGROUND

Inadequate hydration is associated with cardiovascular and kidney disease morbidity and all-cause mortality. Compared with White individuals, Black individuals exhibit a higher prevalence of inadequate hydration, which may contribute to racial health disparities. However, the underlying reasons for these differences in hydration remain unclear.

OBJECTIVE

This cross-sectional study aimed to investigate whether neighborhood deprivation contributes to racial differences in hydration status.

METHODS

We assessed 24 Black and 30 White college students, measuring 24-hour urine osmolality, urine flow rate, urine specific gravity, and plasma copeptin concentration. Participants recorded their food and fluid intake for 3 d to assess total water intake from food and beverages. Neighborhood socioeconomic deprivation was measured using a tract-level Area Deprivation Index.

RESULTS

Black participants exhibited higher urine osmolality (640 [314] compared with 440 [283] mOsm/kg H2O, respectively, P = 0.006) and lower urine flow rate (1.06 [0.65] compared with 1.71 [0.89] ml/min, respectively, P = 0.009) compared with White participants, indicating greater hypohydration among Black participants. Black participants reported lower total water intake from food and beverages than White participants (2.3 ± 0.7 compared with 3.5 ± 1.1 L/day, respectively, P < 0.01). Black participants exhibited higher copeptin than White participants (6.3 [3.1] compared with 4.5 [2.3] pmol/L, P = 0.046), and urine osmolality mediated 67% of the difference (P = 0.027). Black participants reported greater cumulative exposure to neighborhood deprivation during childhood (ages 0-18 y). Furthermore, neighborhood deprivation during childhood was associated with urine specific gravity (P = 0.031) and total water intake from food and beverages (P = 0.042) but did not mediate the racial differences in these measures.

CONCLUSION

Our data suggest that compared with White young adults, Black young adults are hypohydrated and exhibit higher plasma copeptin concentration, and that greater neighborhood deprivation is associated with chronic underhydration irrespective of race. This trial was registered at clinicaltrials.gov as NCT04576338.

The fructose survival hypothesis for obesity

The fructose survival hypothesis proposes that obesity and metabolic disorders may have developed from over-stimulation of an evolutionary-based biologic response (survival switch) that aims to protect animals in advance of crisis. The response is characterized by hunger, thirst, foraging, weight gain, fat accumulation, insulin resistance, systemic inflammation and increased blood pressure. The process is initiated by the ingestion of fructose or by stimulating endogenous fructose production via the polyol pathway. Unlike other nutrients, fructose reduces the active energy (adenosine triphosphate) in the cell, while blocking its regeneration from fat stores. This is mediated by intracellular uric acid, mitochondrial oxidative stress, the inhibition of AMP kinase and stimulation of vasopressin. Mitochondrial oxidative phosphorylation is suppressed, and glycolysis stimulated. While this response is aimed to be modest and short-lived, the response in humans is exaggerated due to gain of 'thrifty genes' coupled with a western diet rich in foods that contain or generate fructose. We propose excessive fructose metabolism not only explains obesity but the epidemics of diabetes, hypertension, non-alcoholic fatty liver disease, obesity-associated cancers, vascular and Alzheimer's dementia, and even ageing. Moreover, the hypothesis unites current hypotheses on obesity. Reducing activation and/or blocking this pathway and stimulating mitochondrial regeneration may benefit health-span. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

Rethinking Vasopressin: New Insights into Vasopressin Signaling and Its Implications

Vasopressin is a highly conserved peptide hormone that has been traditionally associated with water homeostasis. There is accumulating evidence in both humans and animal models that vasopressin is implicated in the regulation of metabolism. This review focuses on the effects that vasopressin exerts on the regulation of glucose and fatty acids with a particular emphasis on the potential repercussions of metabolic dysregulation in kidney disease.

Characterizing fluid intake and physical activity in university students within the United States during the COVID-19 pandemic

PURPOSE

This study determined fluid intake and physical activity behaviors among college students during the COVID-19 pandemic.

METHODS

College students (n = 1014; females, 75.6%) completed an online survey during the Spring 2020 academic semester following the initial global response to the COVID-19 pandemic. Academic standing, habitation situation, and University/College responses to COVID-19 were collected. Participants completed the Godin Leisure-Time Exercise Questionnaire and a 15-item Beverage Questionnaire (BEVQ-15) to determine physical activity level and fluid intake behaviors, respectively.

RESULTS

Females (1920 ± 960 mL) consumed significantly less fluid than males (2400 ± 1270 mL, p < 0.001). Living off-campus (p < 0.01) and living with a spouse/partner (p < 0.01) was associated with increased consumption of alcoholic beverages. 88.7% of participants reported being at least moderately active; however, Black/African American and Asian participants were more likely to be less active than their Caucasian/White counterparts (p < 0.05). Participants reporting no change in habitation in response to COVID-19 had a higher fluid intake (p = 0.002); however, the plain water consumption remained consistent (p = 0.116). While there was no effect of habitation or suspension of classes on physical activity levels (p > 0.05), greater self-reported physical activity was associated with greater fluid intake (std. β = 0.091, p = 0.003).

CONCLUSIONS

Fluid intake among college students during the initial response to the COVID-19 pandemic approximated current daily fluid intake recommendations. Associations between COVID-19-related disruptions (i.e., suspension of classes and changes in habitation) and increased alcohol intake are concerning and may suggest the need for the development of targeted strategies and programming to attenuate the execution of negative health-related behaviors in college students.

Ex vivo LPS-stimulated cytokine production is associated with hydration status in community-dwelling middle-to-older-aged adults

PURPOSE

Suboptimal hydration has been linked to a variety of adverse health outcomes. Few studies have examined the impact of hydration status on immune function, a plausible physiological mechanism underlying these associations. Therefore, we tested how variation in hydration status was associated with circulating pro-inflammatory cytokine levels and ex vivo lipopolysaccharide (LPS)-stimulated pro-inflammatory cytokine production.

METHODS

Blood samples were obtained from a community sample of healthy middle-to-older-aged adults (N = 72). These samples were used to assess serum osmolality, a biomarker of hydration status, and markers of immune function including circulating pro-inflammatory cytokines and stimulated pro-inflammatory cytokine production after 4 and 24 h of incubation with LPS. Multiple linear regressions were used to test the association between serum osmolality (as a continuous variable) and markers of immune function at baseline and after 4 and 24 h adjusting for age, sex, and BMI. These models were re-estimated with serum osmolality dichotomized at the cut-off for dehydration (> 300 mOsm/kg).

RESULTS

While not significantly associated with circulating cytokines (B = - 0.03, p = 0.09), serum osmolality was negatively associated with both 4 h (B = - 0.05, p = 0.048) and 24 h (B = - 0.05, p = 0.03) stimulated cytokine production when controlling for age, sex, and BMI. Similarly, dehydration was associated with significantly lower cytokine production at both 4 h (B = - 0.54, p = 0.02) and 24 h (B = - 0.51, p = 0.02) compared to adequate hydration.

CONCLUSION

These findings suggest that dehydration may be associated with suppressed immune function in generally healthy middle-to-older aged community-dwelling adults. Further longitudinal research is needed to more clearly define the role of hydration in immune function.

Climate change and nephrology

Climate change should be of special concern for the nephrologist, as the kidney has a critical role in protecting the host from dehydration, but it is also a favorite target of heat stress and dehydration. Here we discuss how rising temperatures and extreme heat events may affect the kidney. The most severe presentation of heat stress is heat stroke, which can result in severe electrolyte disturbance and both acute and chronic kidney disease (CKD). However, lesser levels of heat stress also have multiple effects, including exacerbating kidney disease and precipitating cardiovascular events in subjects with established kidney disease. Heat stress can also increase the risk for kidney stones, cause multiple electrolyte abnormalities and induce both acute and chronic kidney disease. Recently there have been multiple epidemics of CKD of uncertain etiology in various regions of the world, including Mesoamerica, Sri Lanka, India and Thailand. There is increasing evidence that climate change and heat stress may play a contributory role in these conditions, although other causes, including toxins, could also be involved. As climate change worsens, the nephrologist should prepare for an increase in diseases associated with heat stress and dehydration.

Middle-age high normal serum sodium as a risk factor for accelerated biological aging, chronic diseases, and premature mortality

BACKGROUND

It is known that some people age faster than others, some people live into old age disease-free, while others develop age-related chronic diseases. With a rapidly aging population and an emerging chronic diseases epidemic, finding mechanisms and implementing preventive measures that could slow down the aging process has become a new challenge for biomedical research and public health. In mice, lifelong water restriction shortens the lifespan and promotes degenerative changes. Here, we test the hypothesis that optimal hydration may slow down the aging process in humans.

METHODS

We performed a cohort analysis of data from the Atherosclerosis Risk in Communities study with middle-age enrollment (45-66 years, n = 15,752) and 25 years follow-up. We used serum sodium, as a proxy for hydration habits. To estimate the relative speed of aging, we calculated the biological age (BA) from age-dependent biomarkers and assessed risks of chronic diseases and premature mortality.

FINDINGS

The analysis showed that middle age serum sodium >142 mmol/l is associated with a 39% increased risk to develop chronic diseases (hazard ratio [HR] = 1.39, 95% confidence interval [CI]:1.18-1.63) and >144 mmol/l with 21% elevated risk of premature mortality (HR = 1.21, 95% CI:1.02-1.45). People with serum sodium >142 mmol/l had up to 50% higher odds to be older than their chronological age (OR = 1.50, 95% CI:1.14-1.96). A higher BA was associated with an increased risk of chronic diseases (HR = 1.70, 95% CI:1.50-1.93) and premature mortality (HR = 1.59, 95% CI 1.39-1.83).

INTERPRETATION

People whose middle-age serum sodium exceeds 142 mmol/l have increased risk to be biologically older, develop chronic diseases and die at younger age. Intervention studies are needed to confirm the link between hydration and aging.

FUNDING

This work was funded by Intramural Research program of the National Heart, Lung, and Blood Institute (NHLBI). The ARIC study has been funded in whole or in part with federal funds from the NHLBI; the National Institutes of Health (NIH); and the Department of Health and Human Services.

Personalized prediction of optimal water intake in adult population by blended use of machine learning and clinical data

Growing evidence suggests that sustained concentrated urine contributes to chronic metabolic and kidney diseases. Recent results indicate that a daily urinary concentration of 500 mOsm/kg reflects optimal hydration. This study aims at providing personalized advice for daily water intake considering personal intrinsic (age, sex, height, weight) and extrinsic (food and fluid intakes) characteristics to achieve a target urine osmolality (U_Osm) of 500 mOsm/kg using machine learning and optimization algorithms. Data from clinical trials on hydration (four randomized and three non-randomized trials) were analyzed. Several machine learning methods were tested to predict U_Osm. The predictive performance of the developed algorithm was evaluated against current dietary guidelines. Features linked to urine production and fluid consumption were listed among the most important features with relative importance values ranging from 0.10 to 0.95. XGBoost appeared the most performing approach (Mean Absolute Error (MAE) = 124.99) to predict U_Osm. The developed algorithm exhibited the highest overall correct classification rate (85.5%) versus that of dietary guidelines (77.8%). This machine learning application provides personalized advice for daily water intake to achieve optimal hydration and may be considered as a primary prevention tool to counteract the increased incidence of chronic metabolic and kidney diseases.

Urinary sodium, iodine, and volume in relation to metabolic syndrome in Mesoamerican children and their parents

BACKGROUND AND AIMS

The roles of sodium or iodine intake on the metabolic syndrome (MetS) etiology remain controversial. We evaluated the associations of 24 h urinary sodium and iodine with MetS among Mesoamerican children and their adult parents.

METHODS AND RESULTS

We conducted a cross-sectional study among 217 school-age children and 478 parents from 9 Mesoamerican cities. Exposures were high 24 h urinary sodium excretion and concentration (>2000 mg/d or mg/L, respectively) and high 24 h urinary iodine excretion and concentration (≥300 μg/d or μg/L, respectively). In children, the outcome was a standardized metabolic score from five criteria analogous to the Adult Treatment Panel (ATP) III criteria. In adults, MetS was defined according to the ATP III criteria. We estimated adjusted mean differences in the metabolic risk score and adjusted prevalence ratios of MetS between exposure categories using multivariable regression. In children, high sodium concentration was associated with a 0.10 units (43% of a SD) higher score (P = 0.001) and high iodine concentration was related to a 0.09 units (39% of a SD) higher score (P = 0.009). Unexpectedly, high 24 h urinary volume was associated with a lower metabolic score. In adults, high 24 h sodium excretion was related to hypertension and high iodine concentration was related to increased MetS prevalence.

CONCLUSION

High sodium and iodine concentrations, but not 24 h iodine excretion, are significantly associated with MetS in children, whereas high 24 h urinary volume is related to a decreased metabolic score. In adults, high iodine concentration tends to be related to increased MetS prevalence, but not 24 h iodine excretion.

Current Hydration Habits: The Disregarded Factor for the Development of Renal and Cardiometabolic Diseases

Improper hydration habits are commonly disregarded as a risk factor for the development of chronic diseases. Consuming an intake of water below recommendations (underhydration) in addition to the substitution of sugar-sweetened beverages (SSB) for water are habits deeply ingrained in several countries. This behavior is due to voluntary and involuntary dehydration; and because young children are exposed to SSB, the preference for a sweet taste is profoundly implanted in the brain. Underhydration and SSB intake lead to mild hyperosmolarity, which stimulates biologic processes, such as the stimulation of vasopressin and the polyol-fructose pathway, which restore osmolarity to normal but at the expense of the continued activation of these biological systems. Unfortunately, chronic activation of the vasopressin and polyol-fructose pathways has been shown to mediate many diseases, such as obesity, diabetes, metabolic syndrome, chronic kidney disease, and cardiovascular disease. It is therefore urgent that we encourage educational and promotional campaigns that promote the evaluation of personal hydration status, a greater intake of potable water, and a reduction or complete halting of the drinking of SSB.

Associations between hydration status, body composition, sociodemographic and lifestyle factors in the general population: a cross-sectional study

Background

Whole-body hydration status is associated with several health outcomes, such as dehydration, edema and hypertension, but little is known about the nonclinical determinants. Therefore, we studied the associations of sex, age, body composition, nutrition, and physical activity on several body hydration measures.

Methods

We assessed sociodemographic variables, dietary habits, and physical activity by questionnaire and body composition by bioelectric impedance analysis (BIA). We compared determinants between the sexes and calculated associations between determinants and BIVA hydration measures by multivariable linear regressions.

Results

A total of 242 adults from the general population (age 18–94, 47% women) were included. Women were younger, smaller, lighter, and had a smaller BMI (kg/m²) than men (p < 0.05). Women had less muscle mass, less visceral fat mass and less extracellular and intracellular water than men (p < 0.001). Women showed less intracellular water per extracellular water than men, while men showed higher phase angle values than women (both p < 0.001). Men had a stronger association of hydration measures with physical activity than women. Both sexes showed a decrease in hydration measures with age.

Conclusions

Sex, age, body composition, and physical activity influence body hydration. There seem to be differences in body water regulation between the sexes. Especially interesting are factors susceptible to preventive measures such as physical activity.

Response to a Water Bolus in Long Term Oral Contraceptive Users

The purpose of our study was to determine the responses to an acute water bolus in long-term oral contraception (OCP) users. Seventeen female volunteers (27 ± 5 y, 64.1 ± 13.7 kg, 39.6 ± 5.9 kg/LBM) provided consent and enrolled in our study. All were long-term OCP users and participated in two trials, one during the active pill (High Hormone, HH) dose of their prescribed OCP and one during the sham pill (Low Hormone, LH) dose. Participants reported to the laboratory euhydrated, were fed breakfast, remained seated for 60 min and were provided a bolus of room temperature water in the amount of 12 mL/kg/LBM. Urine output over 180 min was measured. Nude body mass was measured pre- and post-trial. Urine specific gravity (USG) and urine osmolality were analyzed. Between trials, there were no differences in 3-h total urine volume (P = 0.296), 3-h USG (P = 0.225), 3-h urine osmolality (P = 0.088), or 3-h urine frequency (P = 0.367). Heart rate was not different between trials (P = 0.792) nor over time (P = 0.731). Mean arterial pressure was not different between trials (P = 0.099) nor over time (P = 0.262). Perceived thirst demonstrated a significant main effect for increasing over time regardless of trial (P &lt; 0.001) but there was no difference between trials (P = 0.731). The urgency to void was not different between trials (P = 0.149) nor over time (P = 0.615). Plasma volume change was not different between trials (P = 0.847) (HH: −3.4 ± 5.0, LH post: −3.8 ± 4.5%) and plasma osmolality did not differ between trials (P = 0.290) nor over time (P = 0.967) (HH pre: 290 ± 4, HH post: 289 ± 4, LH pre: 291 ± 4, LH post: 291 ± 4 mosm/L). Blood glucose significantly decreased over time (P &lt; 0.001) but there was no difference between trials (P = 0.780) (HH pre: 95.9 ± 113.9, HH post: 86.8 ± 6.5, LH pre: 95.9 ± 13.5, LH post: 84.6 ± 9.4 mmol/L). Copeptin concentration did not differ between phases of OCP use (P = 0.645) nor from pre- to post-trial (P = 0.787) Despite fluctuations in hormone concentrations, responses to a water bolus seem to be unaffected in OCP users in euhydrated, resting conditions.

Comparing thirst and spot urine concentrations in humans of differing body sizes: An observational study

Elevated body mass index (BMI) has been associated with elevated urine osmolality (UOsm), despite having higher total water intake, but it is unclear if overweight/obese individuals have reduced thirst. In this observational study, we found that overweight/obese individuals had higher UOsm compared to normal-weight individuals (749 ± 37 vs. 624 ± 35 mmol•kg^-1; P < 0.01) while possessing similar thirst ratings (56.4 ± 3 vs. 51.6 ± 3 mm; P = 0.3). In this observational study, overweight/obese individuals possessed more concentrated urine in the absence of higher thirst perception.

Tap Water Consumption and Perceptions in United States Latinx Adults

Insufficient water intake is associated with adverse health outcomes, including chronic disease prevalence and mortality. Adherence to Institute of Medicine total water intake (TWI) recommendations has been low in recent decades, and TWI has been consistently lower in Latinx adults compared with non-Hispanic (NH) white adults. While overall plain water intake is similar between Latinx and NH white adults, Latinx adults consistently consume significantly more bottled water and less tap water. The purpose of this review is to identify factors that may contribute to low water intake and low tap water intake, particularly in Latinx adults. The decision to drink water is complex and is influenced by a myriad of factors including context, environment, eating behaviors, geography, and beverage attributes. Plain water preferences appear to be related, in part, to perceptions of tap water safety as Latinx adults are significantly more likely to perceive their tap water as unsafe compared to NH white adults. Although recent investigations have not consistently or comprehensively evaluated the same factors, we have compiled their findings to describe the complex, interrelated determinants of tap water safety perceptions in Latinx adults. The present review proposes that perceptions are influenced by water insecurity, demographics, prior experiences, organoleptic (sensory) perceptions and availability and sources of information. Existing interventions designed to improve TWI primarily focus on improving access to water and/or educating individuals on the importance of hydration. However, this may not be sufficient in Latinx populations where water is not trusted. Future work should comprehensively assess these factors in Latinx samples and include validated plain water intake, TWI, and hydration status measures. A greater understanding of these relationships could inform interventions to improve TWI and hydration status in Latinx adults.

The Speed of Ingestion of a Sugary Beverage Has an Effect on the Acute Metabolic Response to Fructose

BACKGROUND

The consumption of sweetened beverages is associated with increased risk of metabolic syndrome, cardiovascular disease, and type 2 diabetes mellitus.

OBJECTIVE

We hypothesized that the metabolic effects of fructose in sugary beverages might be modulated by the speed of ingestion in addition to the overall amount.

DESIGN

Thirty healthy subjects free of any disease and medication were recruited into two groups. After overnight fasting, subjects in group 1 drank 500 mL of apple juice over an hour by drinking 125 mL every 15 min, while subjects in group 2 drank 500 mL of apple juice over 5 min. Blood samples were collected at time zero and 15, 30, 60, and 120 min after ingestion to be analyzed for serum glucose, insulin, homeostatic model assessment (HOMA-IR) score, fibroblast growth factor 21, copeptin, osmolarity, sodium, blood urea nitrogen (BUN), lactate, uric acid, and phosphate levels.

RESULTS

Serum glucose, insulin, HOMA-IR, fibroblast growth factor 21, copeptin, osmolarity, sodium, BUN, and lactate levels increased following apple juice ingestion. The increases were greater in the fast-drinking group, which were more significant after 15 min and 30 min compared to baseline. The changes in uric acid were not statistically different between the groups. Phosphate levels significantly increased only in the fast-drinking group.

CONCLUSION

Fast ingestion of 100% apple juice causes a significantly greater metabolic response, which may be associated with negative long-term outcomes. Our findings suggest that the rate of ingestion must be considered when evaluating the metabolic impacts of sweetened beverage consumption.

Associations between urinary hydration markers and metabolic dysfunction: a cross-sectional analysis of NHANES data, 2008-2010

PURPOSE

Growing evidence suggests hydration plays a role in metabolic dysfunction, however data in humans are scarce. This study examined the cross-sectional association between hydration and metabolic dysfunction in a representative sample of the US population.

METHODS

Data from 3961 adult NHANES (National Health and Nutrition Examination Survey) participants (49.8% female; age 46.3 ± 0.5 years) were grouped by quartile of urine specific gravity (U_SG, 2007-2008 cohort) or urine osmolality (U_Osm, 2009-2010 cohort) as measures of hydration. Metabolic dysfunction was assessed by glycemic and insulinemic endpoints and by components of the metabolic syndrome. Multivariate-adjusted linear and logistic regression models were used.

RESULTS

Increasing quartiles of U_SG but not U_Osm was associated with higher fasting plasma glucose (FPG), glycated hemoglobin (all P < 0.01), HOMA-IR and elevated insulin (all P < 0.05). Compared with the lowest quartile, those with the highest U_SG but not U_Osm had greater risk of metabolic syndrome (Q4 vs. Q1, OR (99% CI): 1.6 (1.0, 2.7), P = 0.01) and diabetes (Q4 vs. Q1, OR: 1.8 (1.0, 3.4), P < 0.05). Additionally, those with U_SG > 1.013 or U_Osm > 500 mOsm/kg, common cut-off values for optimal hydration based on retrospective analyses of existing data, had less favorable metabolic markers. In a subset of participants free from diabetes mellitus, impaired kidney function, hypertension and diuretic medication, U_SG remained positively associated with FPG (P < 0.01) and elevated FPG (P < 0.05).

CONCLUSION

These analyses provide population-based evidence that U_SG as a proxy for hydration is associated with glucose homeostasis in NHANES 2007-2008. The same association was not significant when U_Osm was used as a proxy for hydration in the 2009-2010 wave.

CLINICAL TRIAL REGISTRY

Not applicable, as this was a reanalysis of existing NHANES data.

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.

Fluid Intake Restriction Concomitant to Sweetened Beverages Hydration Induce Kidney Damage

Currently, there is the paradox of low water intake but increased intake of sugar-sweetened beverages (SB) in several populations; those habits are associated with an increased prevalence of metabolic derangements and greater chronic disease mortality. Persistent heat dehydration and increased SB intake stimulate the continued release of vasopressin and overactivation of the polyol-fructokinase pathway, synergizing each other, an effect partially mediated by oxidative stress. The objective of the present study was to evaluate whether water restriction concurrent with SB hydration can cause renal damage by stimulating similar pathways as heat dehydration. Three groups of male Wistar rats (n = 6) were fluid restricted; from 10 am to 12 pm animals could rehydrate with tap water (W), or sweetened beverages, one prepared with 11% of a fructose-glucose combination (SB), or with the noncaloric edulcorant stevia (ST). A normal control group of healthy rats was also studied. The animals were followed for 4 weeks. Markers of dehydration and renal damage were evaluated at the end of the study. Fluid restriction and water hydration mildly increased urine osmolality and induced a 15% fall in CrCl while increased the markers of tubular damage by NAG and KIM-1. Such changes were in association with a mild overexpression of V1a and V2 renal receptors, polyol fructokinase pathway overactivation, and increased renal oxidative stress with reduced expression of antioxidant enzymes. Hydration with SB significantly amplified those alterations, while in stevia hydrated rats, the changes were similar to the ones observed in water hydrated rats. These data suggest that current habits of hydration could be a risk factor in developing kidney damage.

Hypotheses about sub-optimal hydration in the weeks before coronavirus disease (COVID-19) as a risk factor for dying from COVID-19

To address urgent need for strategies to limit mortality from coronavirus disease 2019 (COVID-19), this review describes experimental, clinical and epidemiological evidence that suggests that chronic sub-optimal hydration in the weeks before infection might increase risk of COVID-19 mortality in multiple ways. Sub-optimal hydration is associated with key risk factors for COVID-19 mortality, including older age, male sex, race-ethnicity and chronic disease. Chronic hypertonicity, total body water deficit and/or hypovolemia cause multiple intracellular and/or physiologic adaptations that preferentially retain body water and favor positive total body water balance when challenged by infection. Via effects on serum/glucocorticoid-regulated kinase 1 (SGK1) signaling, aldosterone, tumor necrosis factor-alpha (TNF-alpha), vascular endothelial growth factor (VEGF), aquaporin 5 (AQP5) and/or Na⁺/K⁺-ATPase, chronic sub-optimal hydration in the weeks before exposure to COVID-19 may conceivably result in: greater abundance of angiotensin converting enzyme 2 (ACE2) receptors in the lung, which increases likelihood of COVID-19 infection, lung epithelial cells which are pre-set for exaggerated immune response, increased capacity for capillary leakage of fluid into the airway space, and/or reduced capacity for both passive and active transport of fluid out of the airways. The hypothesized hydration effects suggest hypotheses regarding strategies for COVID-19 risk reduction, such as public health recommendations to increase intake of drinking water, hydration screening alongside COVID-19 testing, and treatment tailored to the pre-infection hydration condition. Hydration may link risk factors and pathways in a unified mechanism for COVID-19 mortality. Attention to hydration holds potential to reduce COVID-19 mortality and disparities via at least 5 pathways simultaneously.

Water Researchers Do Not Have a Strategic Plan for Gathering Evidence to Inform Water Intake Recommendations to Prevent Chronic Disease

Confusion has persisted for decades in the United States (U.S.) over how much plain water to drink, despite national water intake recommendations which are based on high quality scientific evidence. This editorial summarizes the definition, alignment and coordination of evidence that informs the current U.S. adequate intake (AI) recommendations for water. It highlights gaps in the evidence that perpetuate confusion and opportunity to address the gaps through strategic planning.

Influence of Nutrient Intake on 24 Hour Urinary Hydration Biomarkers Using a Clustering-Based Approach

Previous work focusing on understanding nutrient intake and its association with total body water homeostasis neglects to consider the collinearity of types of nutrients consumed and subsequent associations with hydration biomarkers. Therefore, the purpose of this study was to analyze consumption patterns of 23 a priori selected nutrients involved in osmotic homeostasis, as well as their association with 24 h urinary hydration markers among fifty African–American first-year college students through a repeated measures observation in a daily living setting. Through application of hierarchical clustering, we were able to identity four clusters of nutrients based on 24 h dietary recalls: (1) alcohol + pinitol, (2) water + calcium + magnesium + erythritol + inositol + sorbitol + xylitol, (3) total calories + total fat + total protein + potassium + sodium + zinc + phosphorous + arginine, and (4) total carbohydrates + total fiber + soluble fiber + insoluble fiber + mannitol + betaine. Furthermore, we found that consumption of nutrients in Cluster #2 was significantly predictive of urine osmolality (p = 0.004); no other clusters showed statistically significant associations with 24 h urinary hydration biomarkers. We conclude that there may be some nutrients that are commonly consumed concomitantly (at the day level), across a variety of settings and populations, and that a limited subset of the clustering of these nutrients may associate with body water status.

The Effect of Acute Hypohydration on Indicators of Glycemic Regulation, Appetite, Metabolism and Stress: A Systematic Review and Meta-Analysis

Evidence synthesizing the effects of acute body water losses on various markers of glycemic regulation, appetite, metabolism, and stress is lacking. Thus, the purpose of this review was to summarize the response of various hormonal changes involved in these physiologic functions to dehydration. A comprehensive literature search for peer-reviewed research in the databases PubMed, Scopus, CINAHL, and SportDiscus was conducted. Studies were included if they contained samples of adults (>18 years) and experimentally induced dehydration as measured by acute body mass loss. Twenty-one articles were eligible for inclusion. Findings suggested cortisol is significantly elevated with hypohydration (standard mean difference [SMD] = 1.12, 95% CI [0.583, 1.67], p < 0.0001). Testosterone was significantly lower in studies where hypohydration was accompanied by caloric restriction (SMD= -1.04, 95% CI [-1.93, -0.14], p = 0.02), however, there were no changes in testosterone in studies examining hypohydration alone (SMD = -0.17, 95% CI [-0.51 0.16], p = 0.30). Insulin and ghrelin were unaffected by acute total body water losses. Acute hypohydration increases markers of catabolism but has a negligible effect on markers of glycemic regulation, appetite, anabolism and stress. Given the brevity of existing research, further research is needed to determine the impact of hydration on glucagon, leptin, peptide YY and the subsequent outcomes relevant to both health and performance.

Hydration in relation to water insecurity, heat index, and lactation status in two small-scale populations in hot-humid and hot-arid environments

OBJECTIVES

This study compared the prevalence of concentrated urine (urine specific gravity ≥1.021), an indicator of hypohydration, across Tsimane' hunter-forager-horticulturalists living in hot-humid lowland Bolivia and Daasanach agropastoralists living in hot-arid Northern Kenya. It tested the hypotheses that household water and food insecurity would be associated with higher odds of hypohydration.

METHODS

This study collected spot urine samples and corresponding weather data along with data on household water and food insecurity, demographics, and health characteristics among 266 Tsimane' households (N = 224 men, 235 women, 219 children) and 136 Daasanach households (N = 107 men, 120 women, 102 children).

RESULTS

The prevalence of hypohydration among Tsimane' men (50.0%) and women (54.0%) was substantially higher (P < .001) than for Daasanach men (15.9%) and women (17.5%); the prevalence of hypohydration among Tsimane' (37.0%) and Daasanach (31.4%) children was not significantly different (P = .33). Multiple logistic regression models suggested positive but not statistically significant trends between household water insecurity and odds of hypohydration within populations, yet some significant joint effects of water and food insecurity were observed. Heat index (2°C) was associated with a 23% (95% confidence interval [CI]: 1.09-1.40, P = .001), 34% (95% CI: 1.18-1.53, P < .0005), and 23% (95% CI: 1.04-1.44, P = .01) higher odds of hypohydration among Tsimane' men, women, and children, respectively, and a 48% (95% CI: 1.02-2.15, P = .04) increase in the odds among Daasanach women. Lactation status was also associated with hypohydration among Tsimane' women (odds ratio = 3.35, 95% CI: 1.62-6.95, P = .001).

CONCLUSION

These results suggest that heat stress and reproductive status may have a greater impact on hydration status than water insecurity across diverse ecological contexts.