Predictors of Water Turnover in Older Adults: A Doubly Labeled Water- and Triaxial Accelerometer-Based Study

BACKGROUND

Water is one of the most essential nutrients for life. The water turnover (WT), total body water (TBW), and total energy expenditure (TEE) can be measured using the doubly labeled water (DLW) method. WT and TBW are lower in older adults than in young adults, and the former are susceptible to dehydration, necessitating to identify predictors of the WT in older adults.

OBJECTIVES

The current study aimed to examine the association between WT and physical activity, physical function, and body composition in Japanese adults aged ≥65 y and identify predictors for WT in this population.

METHODS

This study enrolled 133 older adults (women, n = 61; men, n = 72) aged 65-88 y. WT, TBW, TEE, fat-free mass (FFM), and percent body fat (%Fat) were determined using the DLW method. The fitness age score (FAS) was obtained from 5 physical fitness tests. Physical activity and the step count were assessed using a previously validated triaxial accelerometer. Multiple regression analyses were performed with WT as the dependent variable.

RESULTS

WT was positively associated with weight, physical activity level (PAL), moderate-vigorous physical activity, and TEE, and negatively associated with sedentary behavior. We examined potential predictors for WT using age, sex, height, weight, FFM, %Fat, TEE, PAL, and FAS in older Japanese adults.

CONCLUSIONS

Our results confirmed that age, sex, weight, FFM, TEE, and PAL are the potential predictors of WT in older Japanese adults aged ≥65 y.

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.

Urine specific gravity to identify and predict hydration need in ALS

Introduction: Multiple factors contribute to increased risk of dehydration in amyotrophic lateral sclerosis (ALS), which contributes to shortened survival independent of nutritional status. The assessment of hydration by doubly labeled water is restricted due to the limited availability of this gold standard technique for clinical use. This prompted us to examine the utility of urine-specific gravity (USG) as a predictor of hydration need in ALS subjects. Material and Methods: Using data from a multicenter study of 80 ALS subjects with 250 visits, we conducted a secondary analysis of the original data set from doubly labeled water experiments. We used a cross-section of the data (one visit per 75 subjects) in the model selection step ("test set"), and a repeated measures analysis in the validation step with data from 63 subjects and 142 follow-up visits. The sensitivity to detect inadequate water turnover rate (a surrogate for water intake) was the goal of the predictive model presented for clinical use. Results and discussion: The final predictive model to estimate water requirement included USG, gender, body mass index, and the ALSFRS gross motor subscale score. We developed a best-fit equation to estimate water intake from USG, determine hydration status, and improve clinical care of real-world ALS subjects.

Association between Water and Energy Requirements with Physical Activity and Fat-Free Mass in Preschool Children in Japan

Water and energy are essential for the human body. The doubly labeled water (DLW) method measures water turnover (WT) and total energy expenditure (TEE), which serves as a benchmark for the adequate intake (AI) of water and estimated energy requirements (EER). The objective of the current study was to examine the association of WT and TEE with physical activity and body composition in Japanese preschool children. We included 41 preschool children (22 girls, 19 boys) aged 3–6 in this study. WT, TEE, and fat-free mass (FFM) were obtained using DLW. Physical activity was measured using a triaxial accelerometer and categorized as light (LPA; 1.5–2.9 Metabolic equivalents, METs) and of moderate-to-vigorous intensity (MVPA; ≥3.0 METs). Exercise duration (Ex) was defined as ≥4.0 METs of physical activity. WT and TEE moderately positively correlated with Ex, but not with LPA. WT moderately positively correlated with BW and FFM while TEE strongly. We established predictive equations for WT and TEE using body weight (BW), FFM, step count, and Ex to guide the AI of water and EER in Japanese preschool children. We found that FFM and step count are the determinants of TEE, and that BW and Ex are the determinants of WT in preschool children.

Evolution of water conservation in humans

To sustain life, humans and other terrestrial animals must maintain a tight balance of water gain and water loss each day.^1-3 However, the evolution of human water balance physiology is poorly understood due to the absence of comparative measures from other hominoids. While humans drink daily to maintain water balance, rainforest-living great apes typically obtain adequate water from their food and can go days or weeks without drinking^4-6. Here, we compare isotope-depletion measures of water turnover (L/d) in zoo- and rainforest-sanctuary-housed apes (chimpanzees, bonobos, gorillas, and orangutans) with 5 diverse human populations, including a hunter-gatherer community in a semi-arid savannah. Across the entire sample, water turnover was strongly related to total energy expenditure (TEE, kcal/d), physical activity, climate (ambient temperature and humidity), and fat free mass. In analyses controlling for those factors, water turnover was 30% to 50% lower in humans than in other apes despite humans' greater sweating capacity. Water turnover in zoo and sanctuary apes was similar to estimated turnover in wild populations, as was the ratio of water intake to dietary energy intake (∼2.8 mL/kcal). However, zoo and sanctuary apes ingested a greater ratio of water to dry matter of food, which might contribute to digestive problems in captivity. Compared to apes, humans appear to target a lower ratio of water/energy intake (∼1.5 mL/kcal). Water stress due to changes in climate, diet, and behavior apparently led to previously unknown water conservation adaptations in hominin physiology.

Air temperature and diet influence body composition and water turnover in zoo-living African elephants (Loxodonta africana)

African elephants, the largest land animal, face particular physiological challenges in captivity and the wild. Captive elephants can become over- or under-conditioned with inadequate exercise and diet management. Few studies have quantified body composition or water turnover in elephants, and none to date have examined longitudinal responses to changes in diet or air temperature. Using the stable isotope deuterium oxide (²H₂O), we investigated changes in body mass, estimated fat-free mass (FFM, including fat-free gut content) and body fat in response to a multi-year intervention that reduced dietary energy density for adult African elephants housed at the North Carolina Zoo. We also examined the relationship between air temperature and water turnover. Deuterium dilution and depletion rates were assayed via blood samples and used to calculate body composition and water turnover in two male and three female African elephants at six intervals over a 3-year period. Within the first year after the dietary intervention, there was an increase in overall body mass, a reduction in body fat percentage and an increase in FFM. However, final values of both body fat percentage and FFM were similar to initial values. Water turnover (males: 359 ± 9 l d^-1; females: 241 ± 28 l d^-1) was consistent with the allometric scaling of water use in other terrestrial mammals. Water turnover increased with outdoor air temperature. Our study highlights the physiological water dependence of elephants and shows that individuals have to drink every 2-3 days to avoid critical water loss of approximately 10% body mass in hot conditions.

Thermal stratification and fish thermal preference explain vertical eDNA distributions in lakes

Significant advances have been made towards surveying animal and plant communities using DNA isolated from environmental samples. Despite rapid progress, we lack a comprehensive understanding of the "ecology" of environmental DNA (eDNA), particularly its temporal and spatial distribution and how this is shaped by abiotic and biotic processes. Here, we tested how seasonal variation in thermal stratification and animal habitat preferences influences the distribution of eDNA in lakes. We sampled eDNA depth profiles of five dimictic lakes during both summer stratification and autumn turnover, each containing warm- and cool-water fishes as well as the cold-water stenotherm, lake trout (Salvelinus namaycush). Habitat use by S. namaycush was validated by acoustic telemetry and was significantly related to eDNA distribution during stratification. Fish eDNA became "stratified" into layers during summer months, reflecting lake stratification and the thermal niches of the species. During summer months, S. namaycush, which rarely ventured into shallow waters, could only be detected at the deepest layers of the lakes, whereas the eDNA of warm-water fishes was much more abundant above the thermocline. By contrast, during autumn lake turnover, the fish species assemblage as detected by eDNA was homogenous throughout the water column. These findings contribute to our overall understanding of the "ecology" of eDNA within lake ecosystems, illustrating how the strong interaction between seasonal thermal structure in lakes and thermal niches of species on very localized spatial scales influences our ability to detect species.

Energy Requirement Assessment and Water Turnover in Japanese College Wrestlers Using the Doubly Labeled Water Method

Estimated energy requirements (EERs) are important for sports based on body weight classifications to aid in weight management. The basis for establishing EERs varies and includes self-reported energy intake (EI), predicted energy expenditure, and measured daily energy expenditure. Currently, however, no studies have been performed with male wrestlers using the highly accurate and precise doubly labeled water (DLW) method to estimate energy and fluid requirement. The primary aim of this study was to compare total energy expenditure (TEE), self-reported EI, and the difference in collegiate wrestlers during a normal training period using the DLW method. The secondary aims were to measure the water turnover and the physical activity level (PAL) of the athletes, and to examine the accuracy of two currently used equations to predict EER. Ten healthy males (age, 20.4±0.5 y) belonging to the East-Japan college league participated in this study. TEE was measured using the DLW method, and EI was assessed with self-reported dietary records for ~1 wk. There was a significant difference between TEE (17.9±2.5 MJ•d^-1 [4,283±590 kcal•d^-1]) and self-reported EI (14.4±3.3 MJ•d^-1 [3,446±799 kcal•d^-1]), a difference of 19%. The water turnover was 4.61±0.73 L•d^-1. The measured PAL (2.6±0.3) was higher than two predicted values during the training season and thus the two EER prediction equations produced underestimated values relative to DLW. We found that previous EERs were underestimating requirements in collegiate wrestlers and that those estimates should be revised.

Water requirements of canine athletes during multi-day exercise

BACKGROUND

Exercise increases water requirements, but there is little information regarding water loss in dogs performing multi-day exercise OBJECTIVES: Quantify the daily water turnover of working dogs during multi-day exercise and establish the suitability of SC administration of tracer to determine water turnover.

ANIMALS

Fifteen privately owned Labrador retrievers trained for explosive detection duties and 16 privately owned Alaskan Huskies conditioned for mid-distance racing.

METHODS

All dogs received 0.3 g D₂ O/kg body weight by IV infusion, gavage, or SC injection before the start of a multi-day exercise challenge. Explosive detection dogs conducted 5 days of simulated off-leash explosive detection activity. Alaskan sled dogs completed a mid-distance stage race totaling 222 km in 2 days. Total body water (TBW) and daily water turnover were calculated using both indicator dilution and elimination regression techniques.

RESULTS

Total body water (% of body weight) varied from 60% ± 8.6% in minimally conditioned Labrador retrievers to 74% ± 4.5% in highly conditioned Labrador retrievers. Daily water turnover was as high as 45% of TBW during exercise in cold conditions. There was no effect of sex or speed on daily water turnover. There was good agreement between results calculated using the indicator dilution approach and those calculated using a semilog linear regression approach when indicator isotope was administered IV or SC.

CONCLUSIONS AND CLINICAL IMPORTANCE

Water requirements are influenced primarily by the amount of work done. SC administration of isotope-labeled water offers a simple and accurate alternative method for metabolic studies.

Hydration measured by doubly labeled water in ALS and its effects on survival

We present a study of hydration in ALS patients and its effects on survival. This was a multicenter study over 48 weeks in 80 ALS patients who underwent 250 individual measurements using doubly labeled water (DLW). Total body water (TBW) and water turnover (a surrogate for water intake) were 3.4% and 8.6% lower, respectively, in patients compared to age- and gender-matched healthy controls, and both significantly decreased over study duration. In 20% of patients, water turnover measured over 10 d was 2 standard deviations below the mean value in healthy controls. In a separate clinic cohort of 208 patients, water intake estimated from a de novo equation created from common clinical endpoints was a prognostic indicator of survival. Regardless of nutritional state assessed by BMI, survival was two-fold longer in the group above the median for estimated water intake, suggesting that hydration may be a more important predictor of survival than malnutrition. Risk factors for poor hydration were identified. Water intake equations recommended by US Centers for Medicare and Medicaid Services in healthy elderly were inaccurate for use in ALS patients. We developed equations to estimate TBW and water intake in ALS patients for use in clinics to accurately estimate hydration and improve clinical care.

Validation Testing Demonstrates Efficacy of a 7-Day Fluid Record to Estimate Daily Water Intake in Adult Men and Women When Compared with Total Body Water Turnover Measurement

Background: Mean daily water intake from fluids (WATER-FL) has proven to be difficult to measure because of a range of nonvalidated data collection techniques. Few questionnaires have been validated to estimate WATER-FL against self-reported diaries or urinary hydration markers, which may limit their objectivity.Objectives: The goals of this investigation were 1) to assess the validity of a 7-d fluid record (7dFLR) to measure WATER-FL (WATER-FL-7dFLR) through comparison with WATER-FL as calculated by measuring deuterium oxide (D₂O) disappearance (WATER-FL-D₂O), and 2) to evaluate the reliability of the 7dFLR in measuring WATER-FL.Methods: Participants [n = 96; 51% female; mean ± SD age: 41 ± 14 y; mean ± SD body mass index (in kg/m²): 26.2 ± 5.1] completed body water turnover analysis over 3 consecutive weeks. They completed the 7dFLR and food diaries during weeks 2 and 4 of the observation. The records were entered into nutritional software to determine the water content of all foods and fluids consumed. WATER-FL-D₂O was calculated from water turnover (via the D₂O dilution method), minus water from food and metabolic water. The agreement between the 2 methods of determining WATER-FL were compared according to a Bland-Altman plot at week 2. The test-retest reliability of 7dFLR between weeks 2 and 4 was assessed via intraclass correlation (ICC).Results: The mean ± SD difference between WATER-FL-7dFLR and WATER-FL-D₂O was -131 ± 845 mL/d. In addition, no bias was observed (F_[1,94] = 0.484; R² = 0.006; P = 0.488). When comparing WATER-FL-7dFLR from weeks 2 and 4, no significant difference (mean ± SD difference: 71 ± 75 mL/d; t_[79] = 0.954; P = 0.343) and an ICC of 0.85 (95% CI: 0.77, 0.90) was observed.Conclusions: The main findings of this study were that the use of the 7dFLR is an effective and reliable method to estimate WATER-FL in adults. This style of questionnaire may be extremely helpful for collecting water intake data for large-scale epidemiologic studies.