Ad libitum dehydration is associated with poorer performance on a sustained attention task but not other measures of cognitive performance among middle-to-older aged community-dwelling adults: A short-term longitudinal study.

OBJECTIVE: Hydration status and water intake are critical to physiological health. Despite a popular narrative that dehydration impairs cognitive performance, results are mixed in the literature. Therefore, we tested how hydration status was associated with cognitive performance in an ad libitum state over the course of 3 months. METHODS: Data come from a short-term longitudinal study among middle-to-older aged US adults (n = 78) measured three times (207 observations). All participants were scheduled for 8:00 a.m. visits for the baseline, two-week, and 3-month examinations where they completed surveys, neuropsychological tests to measure cognitive performance, anthropometrics, and a blood draw for biomarker analysis. Serum osmolality (Sosm) was measured as a biomarker of hydration status using osmometry. Four cognitive performance tasks were assessed, including inhibition, working memory, cognitive flexibility, and sustained attention. RESULTS: Panel random effects linear regressions demonstrate that there was an inverse association between dehydration and sustained attention, whereas there were no significant relationships between dehydration and inhibition, working memory, and cognitive flexibility. Adults who were dehydrated (defined as Sosm >300 mOsm/kg) performed substantially worse (B = 0.65 z-score; SE = 0.28; p = .020) on the sustained attention task than those who were not dehydrated adjusting for time fixed effects, age, body mass index, sex, and educational attainment. CONCLUSION: This short-term longitudinal study found that dehydration was only associated with poorer performance on a cognitive performance task that required sustained attention. Maintaining adequate hydration may be increasingly important for middle-to-older aged adults to ensure proper cognitive function, particularly as water needs increase in future climatic scenarios.

Total daily energy expenditure and elevated water turnover in a small-scale semi-nomadic pastoralist society from Northern Kenya.

BACKGROUND: Pastoralists live in challenging environments, which may be accompanied by unique activity, energy, and water requirements. AIM: Few studies have examined whether the demands of pastoralism contribute to differences in total energy expenditure (TEE) and water turnover (WT) compared to other lifestyles. SUBJECTS AND METHODS: Accelerometer-derived physical activity, doubly labelled water-derived TEE and WT, and anthropometric data were collected for 34 semi-nomadic Daasanach adults from three northern Kenyan communities with different levels of pastoralist activity. Daasanach TEEs and WTs were compared to those of other small-scale and industrialised populations. RESULTS: When modelled as a function of fat-free-mass, fat-mass, age, and sex, TEE did not differ between Daasanach communities. Daasanach TEE (1564-4172 kcal/day) was not significantly correlated with activity and 91% of TEEs were within the range expected for individuals from comparison populations. Mean WT did not differ between Daasanach communities; Daasanach absolute (7.54 litres/day men; 7.46 litres/day women), mass-adjusted, and TEE-adjusted WT was higher than most populations worldwide. CONCLUSIONS: The similar mass-adjusted TEE of Daasanach and industrialised populations supports the hypothesis that habitual TEE is constrained, with physically demanding lifestyles necessitating trade-offs in energy allocation. Elevated WT in the absence of elevated TEE likely reflects a demanding active lifestyle in a hot, arid climate.

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.

Extreme climatic events and human biology and health: A primer and opportunities for future research.

Extreme climatic events are increasing in frequency, leading to hotter temperatures, flooding, droughts, severe storms, and rising oceans. This special issue brings together a collection of seven articles that describe the impacts of extreme climatic events on a diverse set of human biology and health outcomes. The first two articles cover extreme temperatures extending from extreme heat to cold and changes in winter weather and the respective implications for adverse health events, human environmental limits, well-being, and human adaptability. Next, two articles cover the effects of exposures to extreme storms through an examination of hurricanes and cyclones on stress and birth outcomes. The following two articles describe the effects of extreme flooding events on livelihoods, nutrition, water and food insecurity, diarrheal and respiratory health, and stress. The last article examines the effects of drought on diet and food insecurity. Following a brief review of each extreme climatic event and articles covered in this special issue, I discuss future research opportunities-highlighting domains of climate change and specific research questions that are ripe for biological anthropologists to investigate. I close with a description of interdisciplinary methods to assess climate exposures and human biology outcomes to aid the investigation of the defining question of our time - how climate change will affect human biology and health. Ultimately, climate change is a water, food, and health problem. Human biologists offer a unique perspective for a combination of theoretical, methodological, and applied reasons and thus are in a prime position to contribute to this critical research agenda.

When the flood passes, does health return? A short panel examining water and food insecurity, nutrition, and disease after an extreme flood in lowland Bolivia.

OBJECTIVES: Flooding is the most frequent extreme-weather disaster and disproportionately burdens marginalized populations. This article examines how food and water insecurity, blood pressure (BP), nutritional status, and diarrheal and respiratory illnesses changed during the 2 months following a historic flood in lowland Bolivia. METHODS: Drawing on longitudinal data from Tsimane' forager-horticulturalist (n = 118 household heads; n = 129 children) directly after a historic 2014 flood and ~2 months later, we use fixed effects linear regression and random effects logistic regression models to test changes in the markers of well-being and health over the recovery process. RESULTS: Results demonstrated that water insecurity scores decreased significantly 2 month's postflood, while food insecurity scores remained high. Adults' systolic and diastolic BP significantly declined 2 months after the flood's conclusion. Adults experienced losses in measures of adiposity (BMI, sum of four skinfolds, waist circumference). Children gained weight and BMI-for-age Z-scores indicating buffering of children by adults from food stress that mainly occurred in the community closer to the main market town with greater access to food aid. Odds of diarrhea showed a nonsignificant decline, while cough increased significantly for both children and adults 2 months postflood. CONCLUSIONS: Water insecurity and BP improved during the recovery process, while high levels of food insecurity persisted, and nutritional stress and respiratory illness worsened. Not all indicators of well-being and health recover at the same rate after historic flooding events. Planning for multiphase recovery is critical to improve health of marginalized populations after flooding.

Early childhood growth in Daasanach pastoralists of Northern Kenya: Distinct patterns of faltering in linear growth and weight gain.

OBJECTIVES: Investigations of early childhood growth among small-scale populations are essential for understanding human life history variation and enhancing the ability to serve such communities through global public health initiatives. This study characterizes early childhood growth trajectories and identifies differences in growth patterns relative to international references among Daasanach semi-nomadic pastoralist children living in a hot, arid region of northern Kenya. METHODS: A large sample of height and weight measures were collected from children (N = 1756; total observations = 4508; age = 0-5 years) between 2018 and 2020. Daasanach growth was compared to international reference standards and Daasanach-specific centile growth curves and pseudo-velocity models were generated using generalized additive models for location scale and size. RESULTS: Compared to World Health Organization (WHO) reference, relatively few Daasanach children were stunted (14.3%), while a large proportion were underweight (38.5%) and wasted (53.6%). Additionally, Daasanach children had a distinctive pattern of growth, marked by an increase in linear growth velocity after 24 months of age and relatively high linear growth velocity throughout the rest of early childhood. CONCLUSIONS: These results identify a unique pattern of early childhood growth faltering among children in a small-scale population and may reflect a thermoregulatory adaptation to their hot, arid environment. As linear growth and weight gain remain important indicators of health, the results of this study provide insight into growth velocity variations. This study has important implications for global public health efforts to identify and address sources of early growth faltering and undernutrition in small-scale populations.

Water Insecurity, Water Borrowing, and Psychosocial Stress Among Daasanach Pastoralists in Northern Kenya.

This article quantifies Daasanach water insecurity experiences in Northern Kenya, examines how water insecurity is associated with water borrowing and psychosocial stress, and evaluates if water borrowing mitigates the stress from water insecurity. Of 133 households interviewed in 7 communities, 94% were water insecure and 74.4% borrowed water three or more times in the prior month. Regression analyses demonstrate water borrowing frequency moderates the relationship between water insecurity and psychosocial stress. Only those who rarely or never borrowed water reported greater stress with higher water insecurity. The coping mechanism of water borrowing may help blunt water insecurity-related stress.

Using Water Intake Dietary Recall Data to Provide a Window into US Water Insecurity.

BACKGROUND: In the United States, problems with the provision of safe, affordable water have resulted in an increasing number of adults who avoid their tap water, which could indicate underlying water insecurity. Dietary recalls provide critical nutritional surveillance data, yet have been underexplored as a water insecurity monitoring tool. OBJECTIVES: This article aims to demonstrate how water intake variables from dietary recall data relate to and predict a key water insecurity proxy, that is, tap water avoidance. METHODS: Using 2005-2018 NHANES data from 32,329 adults, I examine distributions and trends of mean intakes of total, plain (sum of tap and bottled water), tap, and bottled water, and percentage consuming no tap and exclusive bottled water. Second, I use multiple linear and logistic regressions to test how tap water avoidance relates to plain water intake and sugar-sweetened beverage (SSB) consumption. Next, I use receiver operating characteristics (ROC) curves to test the predictive accuracy of no plain water, no tap, and exclusive bottled water intake, and varying percentages of plain water consumed from tap water compared with tap water avoidance. RESULTS: Trends indicate increasing plain water intake between 2005 and 2018, driven by increasing bottled water intake. In 2017-18, 51.4% of adults did not drink tap water on a given day, whereas 35.8% exclusively consumed bottled water. Adults who avoided their tap water consumed less tap and plain water, and significantly more bottled water and SSBs on a given day. No tap intake and categories of tap water intake produced 77% and 78% areas under the ROC curve in predicting tap water avoidance. CONCLUSIONS: This study demonstrates that water intake variables from dietary recalls can be used to accurately predict tap water avoidance and provide a window into water insecurity. Growing reliance on bottled water could indicate increasing concerns about tap water.

Variation in urine osmolality throughout pregnancy: a longitudinal, randomized-control trial among women with overweight and obesity.

PURPOSE: Water needs increase during pregnancy, and proper hydration is critical for maternal and fetal health. This study characterized weekly hydration status changes throughout pregnancy and examined change in response to a randomized, behavioral intervention. An exploratory analysis tested how underhydration during pregnancy was associated with birth outcomes. METHODS: The Healthy Mom Zone Study is a longitudinal, randomized-control trial intervention aiming to regulate gestational weight gain (GWG) in pregnant women with overweight/obesity (n = 27). Fourteen women received standard of care; 13 women additionally received weekly guidance on nutrition, physical activity, water intake, and health-promoting behaviors. Hydration status was measured weekly via overnight urine osmolality (Uosm) from ~ 8-36 weeks gestation; underhydration was dichotomized (Uosm ≥ 500 mOsm/kg). Gestational age- and sex-standardized birth weight and length z scores and percentiles were calculated. We used mixed-effect and linear regression models to test covariate-adjusted relationships. RESULTS: No differences existed in Uosm or other characteristics between control and intervention women at baseline. Significant interactions (p = 0.01) between intervention and week of pregnancy on Uosm indicated intervention women maintained lower Uosm, whereas control women had a significant quadratic (inverse-U) relationship and greater Uosm in the second and early third trimesters. Results were consistent across robustness and sensitivity checks. Exploratory analyses suggest underhydration was associated with birth weight, but not length, in opposite ways in the second vs. third trimester. CONCLUSION: A multi-component behavioral intervention helped women with overweight/obesity maintain better hydration throughout pregnancy. Future studies should confirm birth outcome results as they have important implications for early life nutrition. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03945266; registered May 10, 2019 retrospectively.

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.

Examining recent trends in the racial disparity gap in tap water consumption: NHANES 2011-2018.

OBJECTIVE: As tap water distrust has grown in the USA with greater levels among Black and Hispanic households, we aimed to examine recent trends in not drinking tap water including the period covering the US Flint Water Crisis and racial/ethnic disparities in these trends. DESIGN: Cross-sectional analysis. We used log-binomial regressions and marginal predicted probabilities to examine US nationally representative trends in tap and bottled water consumption overall and by race/ethnicity. SETTING: The National Health and Nutrition Examination Survey data, 2011-2018. PARTICIPANTS: Nationally representative sample of 9439 children aged 2-19 years and 17 268 adults. RESULTS: Among US children and adults, respectively, in 2017-2018 there was a 63 % (adjusted prevalence ratio (PR): 1·63, 95 % CI (1·25, 2·12), P < 0·001)) and 40 % (PR: 1·40, 95 % CI (1·16, 1·69), P = 0·001)) higher prevalence of not drinking tap water compared to 2013-2014 (pre-Flint Water Crisis). For Black children and adults, the probability of not drinking tap water increased significantly from 18·1 % (95 % CI (13·4, 22·8)) and 24·6 % (95 % CI (20·7, 28·4)) in 2013-2014 to 29·3 % (95 % CI (23·5, 35·1)) and 34·5 % (95 % CI (29·4, 39·6)) in 2017-2018. Among Hispanic children and adults, not drinking tap water increased significantly from 24·5 % (95 % CI (19·4, 29·6)) and 27·1 % (95 % CI (23·0, 31·2)) in 2013-2014 to 39·7 % (95 % CI (32·7, 46·8)) and 38·1 % (95 % CI (33·0, 43·1)) in 2017-2018. No significant increases were observed among Asian or White persons between 2013-2014 and 2017-2018. Similar trends were found in bottled water consumption. CONCLUSIONS: This study found persistent disparities in the tap water consumption gap from 2011 to 2018. Black and Hispanics' probability of not drinking tap water increased following the Flint Water Crisis.

The co-occurrence of water insecurity and food insecurity among Daasanach pastoralists in northern Kenya.

OBJECTIVE: Water plays a critical role in the production of food and preparation of nutritious meals, yet few studies have examined the relationship between water and food insecurity. The primary objective of this study, therefore, was to examine how experiences of household water insecurity (HWI) relate to experiences of household food insecurity (HFI) among a pastoralist population living in an arid, water-stressed region of northern Kenya. DESIGN: We implemented the twelve-item Household Water Insecurity Experiences (HWISE, range 0-36) Scale and the nine-item Household Food Insecurity Access Scale (HFIAS, range 0-27) in a cross-sectional survey to measure HWI and HFI, respectively. Data on socio-demographic characteristics and intake of meat and dairy in the prior week were collected as covariates of interest. SETTING: Northern Kenya, June-July 2019. PARTICIPANTS: Daasanach pastoralist households (n 136) from seven communities. RESULTS: In the prior 4 weeks, 93·4 % and 98·5 % of households had experienced moderate-to-severe HWI and HFI, respectively. Multiple linear regression analyses indicated a strong association between HWI and HFI. Each point higher HWISE score was associated with a 0·44-point (95 % CI: 0·22, 0·66, P = 0·003) higher HFIAS score adjusting for socio-economic status and other covariates. CONCLUSIONS: These findings demonstrate high prevalence and co-occurrence of HWI and HFI among Daasanach pastoralists in northern Kenya. This study highlights the need to address HWI and HFI simultaneously when developing policies and interventions to improve the nutritional well-being of populations whose subsistence is closely tied to water availability and access.

Evaluating Differences in Whole Blood, Serum, and Urine Screening Tests for Zika Virus, Puerto Rico, USA, 2016.

We evaluated nucleic acid amplification testing (NAAT) for Zika virus on whole-blood specimens compared with NAAT on serum and urine specimens among asymptomatic pregnant women during the 2015-2016 Puerto Rico Zika outbreak. Using NAAT, more infections were detected in serum and urine than in whole blood specimens.

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.

Cognitive performance in relation to hydration status and water intake among older adults, NHANES 2011-2014.

PURPOSE: Risks of dehydration and cognitive decline increase with advancing age, yet the relation between dehydration, water intake, and cognitive performance among older adults remains understudied. METHODS: Using data from the 2011-2014 cycles of the Nutrition and Health Examination Survey (NHANES), we tested if calculated serum osmolarity (Sosm) and adequate intake (AI) of water among women (n = 1271) and men (n = 1235) ≥ 60 years old were associated with scores of immediate and delayed recall, verbal fluency, and attention/processing speed. Sosm was categorized as < 285 (hyperhydrated), 285-289, 290-294, 295-300, or > 300 (dehydrated) mmol/L. AI of water was defined as ≥ 2 L/day for women and ≥ 2.5 L/day for men. RESULTS: Women with Sosm between 285 and 289 mmol/L scored 3.2-5.1 points higher on the Digit Symbol Substitution test (DSST) of attention/processing speed than women in other Sosm categories (P values < 0.05). There was evidence of a curvilinear relationship between DSST scores and Sosm among women and men (P values for quadratic terms < 0.02). Meeting an alternative AI on water intake of ≥ 1 mL/kcal and ≥ 1500 mL, but not the sex-specific AI, was associated with scoring one point higher on a verbal fluency test (P = 0.02) and two points higher on the DSST (P = 0.03) among women. Significant negative associations between dehydration or inadequate water intake and test scores were not observed among men. CONCLUSION: Hydration status and water intake were moderately associated with attention/processing speed among females. Future work should consider the effects of both dehydration and overhydration on cognitive function and investigate potential sex differences in cognitive responses to hydration status.

Water borrowing is consistently practiced globally and is associated with water-related system failures across diverse environments.

Water problems due to scarcity, inaccessibility, or poor quality are a major barrier to household functioning, livelihood, and health globally. Household-to-household water borrowing has been posited as a strategy to alleviate unmet water needs. However, the prevalence and predictors of this practice have not been systematically examined. Therefore, we tested whether water borrowing occurs across diverse global contexts with varying water problems. Second, we tested if household water borrowing is associated with unmet water needs, perceived socio-economic status (SES), and/or water-related system failures, and if water access moderated (or changed) these relationships. Using survey data from the Household Water Insecurity Experiences (HWISE) study from 21 sites in 19 low- and middle-income countries (n = 5495 households), we found that household-to-household water borrowing was practiced in all 21 sites, with 44.7% (11.4-85.4%) of households borrowing water at least once the previous month. Multilevel mixed-effect logistic regression models demonstrate that high unmet water needs (odds ratio [OR] = 2.86], 95% confidence interval [CI] = 2.09-3.91), low perceived SES (OR = 1.09; 95% CI = 1.05-1.13), and water-related system failures (23-258%) were all significantly associated with higher odds of water borrowing. Significant interactions (all p < 0.01) between water access, unmet water needs, and water-related system failures on water borrowing indicate that water access moderates these relationships. These data are the first to demonstrate that borrowing water is commonly used by households around the world to cope with water insecurity. Due to how prevalent water borrowing is, its implications for social dynamics, resource allocation, and health and well-being are likely vast but severely under-recognized.

Corrigendum to "Water borrowing is consistently practiced globally and is associated with water-related system failures across diverse environments" [Global Environ. Change 64 (2020) 102148].

[This corrects the article PMC7566692.].

Biobehavioral variation in human water needs: How adaptations, early life environments, and the life course affect body water homeostasis.

Body water homeostasis is critical for optimal physiological and cognitive function for humans. The majority of research has illustrated the negative biological consequences of failing to meet water needs. The human body has several mechanisms for detecting, regulating, and correcting body water deficits and excesses. However, variation exists in total water intake and how people meet those water needs as well as thirst thresholds and how well people tolerate water restriction. An evolutionary and developmental framework provides an underexplored perspective into human water needs by examining how adaptations, early life experiences and environments, as well as life course changes in health states and behaviors may shape these critical factors in body water homeostasis. This article first reviews biological and behavioral adaptations to water scarcity among animals and humans. It then examines human variation in water intake in a mostly water secure environment through the analysis of National Health and Nutrition Examination Survey dietary data and the link between water intake patterns and hydration biomarkers. Next, it reviews existing evidence of how maternal water restriction in utero and during lactation shape vasopressin release, thirst thresholds, drinking patterns, and body water homeostasis for the infant. Early life water restriction appears to have implications for hydration status, body size, and cardiovascular health. Finally, it examines how life course changes in health states and behaviors, including obesity, sleep, and parasitic infection, affect body water homeostasis. This article poses new questions about the plasticity and shaping of human water needs, thirst, and hydration behaviors.

Measuring Human Water Needs.

Water connects the environment, culture, and biology, yet only recently has it emerged as a major focus for research in human biology. To facilitate such research, we describe methods to measure biological, environmental, and perceptual indicators of human water needs. This toolkit provides an overview of methods for assessing different dimensions of human water need, both well-established and newly-developed. These include: (a) markers of hydration (eg, urine specific gravity, doubly labeled water) important for measuring the impacts of water need on human biological functioning; (b) methods for measuring water quality (eg, digital colorimeter, membrane filtration) essential for understanding the health risks associated with exposure to microbiological, organic, metal, inorganic nonmental, and other contaminants; and (c) assessments of household water insecurity status that track aspects of unmet water needs (eg, inadequate water service, unaffordability, and experiences of water insecurity) that are directly relevant to human health and biology. Together, these methods can advance new research about the role of water in human biology and health, including the ways that insufficient, unsafe, or insecure water produces negative biological and health outcomes.

Age-related decline in urine concentration may not be universal: Comparative study from the U.S. and two small-scale societies.

OBJECTIVES: Evidence from industrialized populations suggests that urine concentrating ability declines with age. However, lifestyle factors including episodic protein intake and low hypertension may help explain differences between populations. Whether this age-related decline occurs among small-scale populations with active lifestyles and non-Western diets is unknown. We test the universality of age-related urine concentration decline. MATERIALS AND METHODS: We used urine specific gravity (Usg) and urine osmolality (Uosm) data from 15,055 U.S. nonpregnant adults without kidney failure aged 18-80 in 2007-2012 participating in the National Health and Nutrition Examination Survey (NHANES). We tested the relationship of age on urine concentration biomarkers with multiple linear regressions using survey commands. We compared results to longitudinal data on Usg from 116 Tsimane' forager-horticulturalists (266 observations) adults aged 18-83 in 2013-2014 from Lowland Bolivia, and to 38 Hadza hunter-gatherers (156 observations) aged 18-75 in 2010-2015 from Tanzania using random-effects panel linear regressions. RESULTS: Among U.S. adults, age was significantly negatively associated with Usg (Adjusted beta [B] = -0.0009 g/mL/10 years; SE = 0.0001; p < 0.001) and Uosm (B = -28.1 mOsm/kg/10 yr; SE = 2.4; p < 0.001). In contrast, among Tsimane' (B = 0.0003 g/mL/10 yr; SE = 0.0002; p = 0.16) and Hadza (B = -0.0004 g/mL/10 yr; SE = 0.0004; p = 0.29) age was not associated with Usg. Older Tsimane' and Hadza exhibited similar within-individual variability in Usg equivalent to younger adults. DISCUSSION: While U.S. adults exhibited age-related declines in urine concentration, Tsimane' and Hadza adults did not exhibit the same statistical decline in Usg. Mismatches between evolved physiology and modern environments in lifestyle may affect kidney physiology and disease risk.