Hydration for health hypothesis: a narrative review of supporting evidence.

PURPOSE: An increasing body of evidence suggests that excreting a generous volume of diluted urine is associated with short- and long-term beneficial health effects, especially for kidney and metabolic function. However, water intake and hydration remain under-investigated and optimal hydration is poorly and inconsistently defined. This review tests the hypothesis that optimal chronic water intake positively impacts various aspects of health and proposes an evidence-based definition of optimal hydration. METHODS: Search strategy included PubMed and Google Scholar using relevant keywords for each health outcome, complemented by manual search of article reference lists and the expertise of relevant practitioners for each area studied. RESULTS: The available literature suggest the effects of increased water intake on health may be direct, due to increased urine flow or urine dilution, or indirect, mediated by a reduction in osmotically -stimulated vasopressin (AVP). Urine flow affects the formation of kidney stones and recurrence of urinary tract infection, while increased circulating AVP is implicated in metabolic disease, chronic kidney disease, and autosomal dominant polycystic kidney disease. CONCLUSION: In order to ensure optimal hydration, it is proposed that optimal total water intake should approach 2.5 to 3.5 L day-1 to allow for the daily excretion of 2 to 3 L of dilute (< 500 mOsm kg-1) urine. Simple urinary markers of hydration such as urine color or void frequency may be used to monitor and adjust intake.

Under What Conditions do Water-Intervention Studies Significantly Improve Child Body Weight?

There are particular conditions that may optimize the effects of drinking-water interventions on body weight change and risk of obesity. Strategic planning to create and sustain conditions for optimal effects of drinking water may maximize the impact of school-based interventions to reduce childhood obesity. This paper proposes questions about the target population, type of diet and activity level that will be maintained during the intervention, and planned intervention message(s). The proposed questions are motivated by conditions associated with significant effects of drinking water in randomized controlled trials. They are discussed in relation to conditions underlying the recently successful school-based drinking-water intervention in New York City. If conditions allow, school-based drinking-water interventions have the potential to efficiently benefit millions of children worldwide, who are at risk of becoming obese.

Healthy apple program to support child care centers to alter nutrition and physical activity practices and improve child weight: a cluster randomized trial.

BACKGROUND: North Carolina Nutrition and Physical Activity Self-Assessment for Child Care (NAP SACC) resources improve child body mass index (BMI) when the resources are introduced by nurses to child care providers, and offered with workshops and incentives. In San Francisco, public health and child care agencies partnered to adapt NAP SACC resources into an annual "Healthy Apple" quality improvement program (HAP). METHODS: This cluster randomized controlled trial pilot-tested integration of the HAP with bi-annual public health screenings by nurses. All child care centers that participated in Child Care Health Program (CCHP) screenings in San Francisco in 2011-2012 were offered routine services plus HAP in 2012-2013 (CCHP + HAP, n = 19) or routine services with delayed HAP in 2014-2015 (CCHP + HAP Delayed, n = 24). Intention-to-treat analyses (robust SE or mixed models) used 4 years of screening data from 12 to 17 CCHP + HAP and 17 to 20 CCHP + HAP Delayed centers, regarding 791 to 945 children ages 2 to 5y, annually. Year-specific, child level models tested if children in CCHP + HAP centers had greater relative odds of exposure to 3 index best practices and smaller Autumn-to-Spring changes in BMI percentile and z-score than children in CCHP + HAP Delayed centers, controlling for age, sex, and Autumn status. Multi-year, child care center level models tested if HAP support modified year-to-year changes (2013-2014 and 2014-2015 vs 2011-2012) in child care center annual mean Autumn-to-Spring BMI changes. RESULTS: In 2011-2012, the CCHP + HAP and CCHP + HAP Delayed centers had similar index practices (<15% of children were exposed to a physical activity curriculum, staff joining in active play, and drinking water pitchers) and annual BMI changes. In 2013-2014: 60% of children in CCHP + HAP centers were exposed to the 3 index practices vs 19% in CCHP + HAP Delayed centers; Mean (SE) child BMI percentile (-2.6 (0.9), p = 0.003) and z-score (-0.08 (0.03), p = 0.007) decreased more in CCHP + HAP vs CCHP + HAP Delayed centers. In 2014-2015, after all centers were offered HAP, the index practices and BMI changes were improved for all centers vs 2011-2012. CONCLUSIONS: Integration of the HAP with existing public health nursing services was associated with significantly more children exposed to best practices and improvement in child BMI change. The results warrant continued integration of HAP into local public health infrastructure. TRIAL REGISTRATION: ISRCTN18857356 (24/04/2015) Retrospectively registered.

Conceptual framework for preterm birth review in San Francisco.

Preterm birth persists as a leading cause of infant mortality and morbidity despite decades of intervention effort. Intervention null effects may reflect failure to account for social determinants of health (SDH) or jointly acting risk factors. In some communities, persistent preterm birth trends and disparities have been consistently associated with SDH such as race/ethnicity, zip code, and housing conditions. Health authorities recommend conceptual frameworks for targeted action on SDH and precision public health approaches for preterm birth prevention. We document San Francisco, California's experience identifying the need, rationale, methods, and pilot work for developing a conceptual framework for preterm birth review (PTBR) in San Francisco. The PTBR conceptual framework is intended to enable essential public health services in San Francisco that prevent a range of preterm birth phenotypes by guiding plans for data collection, hypothesis testing, analytical methods, reports, and intervention strategy. Key elements of the PTBR conceptual framework are described including, 10 domains of SDH, 9 domains at the whole person level, such as lived experience and health behaviors, 8 domains at the within-person level, such as biomarkers and clinical measures, 18 preterm birth phenotypes, and the interconnections between domains. Assumptions for the PTBR conceptual framework were supported by a scoping review of literature on SDH effects on preterm birth, health authority consensus reports, and PTBR pilot data. Researcher and health authority interest in each of the domains warrants the framework to prompt systematic consideration of variables in each proposed domain. PTBR pilot data, illustrated in heatmaps, confirm the feasibility of data collection based on the framework, prevalence of co-occurring risk factors, potential for joint effects on specific preterm birth phenotypes, and opportunity for intervention to block SDH effects on preterm birth. The proposed PTBR conceptual framework has practical implications for specifying (1) population groups at risk, (2) grids or heatmap visualization of risk factors, (3) multi-level analyses, and (4) multi-component intervention design in terms of patterns of co-occurring risk factors. Lessons learned about PTBR data collection logistics, variable choice, and data management will be incorporated into future work to build PTBR infrastructure based on the PTBR conceptual framework.

Change in Metabolomic Profile Associated with an Average Increase in Plain Water Intake of >+ 1 L/Day, Sustained Over 4 Weeks, in Healthy Young Men with Initial Total Water Intake Below 2 L/Day.

Background/Aims: Cells adapt to chronic extracellular hypotonicity by altering metabolism. Corresponding effects of sustained hypotonic exposure at the whole-person level remain to be confirmed and characterized in clinical and population-based studies. This analysis aimed to 1) describe changes in urine and serum metabolomic profiles associated with four weeks of sustained > +1 L/d drinking water in healthy, normal weight, young men, 2) identify metabolic pathways potentially impacted by chronic hypotonicity, and 3) explore if effects of chronic hypotonicity differ by type of specimen and/or acute hydration condition. Materials: Untargeted metabolomic assays were completed for specimen stored from Week 1 and Week 6 of the Adapt Study for four men (20-25 years) who changed hydration classification during that period. Each week, first-morning urine was collected after overnight food and water restriction, and urine (t+60 min) and serum (t+90 min) were collected after a 750 mL bolus of drinking water. Metaboanalyst 5.0 was used to compare metabolomic profiles. Results: In association with four weeks of > + 1 L/d drinking water, urine osmolality decreased below 800 mOsm/kg H2O and saliva osmolality decreased below 100 mOsm/kg H2O. Between Week 1 and Week 6, 325 of 562 metabolic features in serum changed by 2-fold or more relative to creatinine. Based on hypergeometric test p-value <0.05 or Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway impact factor >0.2, the sustained > + 1 L/d of drinking water was associated with concurrent changes in carbohydrate, protein, lipid, and micronutrient metabolism, a metabolomic pattern of carbohydrate oxidation via the tricarboxylic acid (TCA) cycle, instead of glycolysis to lactate, and a reduction of chronic disease risk factors in Week 6. Similar metabolic pathways appeared potentially impacted in urine, but the directions of impact differed by specimen type. Conclusion: In healthy, normal weight, young men with initial total water intake below 2 L/d, sustained > + 1 L/d drinking water was associated with profound changes in serum and urine metabolomic profile, which suggested normalization of an aestivation-like metabolic pattern and a switch away from a Warburg-like pattern. Further research is warranted to pursue whole-body effects of chronic hypotonicity that reflect cell-level effects and potential beneficial effects of drinking water on chronic disease risk.

What is the cell hydration status of healthy children in the USA? Preliminary data on urine osmolality and water intake.

OBJECTIVE: Hyperosmotic stress on cells limits many aspects of cell function, metabolism and health. International data suggest that schoolchildren may be at risk of hyperosmotic stress on cells because of suboptimal water intake. The present study explored the cell hydration status of two samples of children in the USA. DESIGN: Cross-sectional study describing the urine osmolality (an index of hyperosmotic cell shrinkage) and water intake of convenience samples from Los Angeles (LA) and New York City (NYC). SETTING: Each participant collected a urine sample at an outpatient clinic on the way to school on a weekday morning in spring 2009. Each was instructed to wake, eat, drink and do as usual before school, and complete a dietary record form describing the type and amounts of all foods and beverages consumed after waking, before giving the sample. SUBJECTS: The children (9-11 years) in LA (n 337) and NYC (n 211) considered themselves healthy enough to go to school on the day they gave the urine sample. RESULTS: Elevated urine osmolality (>800 mmol/kg) was observed in 63 % and 66 % of participants in LA and NYC, respectively. In multivariable-adjusted logistic regression models, elevated urine osmolality was associated with not reporting intake of drinking water in the morning (LA: OR = 2·1, 95 % CI 1·2, 3·5; NYC: OR = 1·8, 95 % CI 1·0, 3·5). Although over 90 % of both samples had breakfast before giving the urine sample, 75 % did not drink water. CONCLUSIONS: Research is warranted to confirm these results and pursue their potential health implications.

The association of COVID-19 infection in pregnancy with preterm birth: A retrospective cohort study in California.

INTRODUCTION: Our understanding of the association between coronavirus disease 19 (COVID-19) and preterm or early term birth among racially and ethnically diverse populations and people with chronic medical conditions is limited. METHODS: We determined the association between COVID-19 and preterm (PTB) birth among live births documented by California Vital Statistics birth certificates between July 2020 and January 2021 (n=240,147). We used best obstetric estimate of gestational age to classify births as very preterm (VPTB, <32 weeks), PTB (< 37 weeks), early term (37 and 38 weeks), and term (39-44 weeks), as each confer independent risks to infant health and development. Separately, we calculated the joint effects of COVID-19 diagnosis, hypertension, diabetes, and obesity on PTB and VPTB. FINDINGS: COVID-19 diagnoses on birth certificates increased for all racial/ethnic groups between July 2020 and January 2021 and were highest for American Indian/Alaska Native (12.9%), Native Hawaiian/Pacific Islander (11.4%), and Latinx (10.3%) birthing people. COVID-19 diagnosis was associated with an increased risk of VPTB (aRR 1.6, 95% CI [1.4, 1.9]), PTB (aRR 1.4, 95% CI [1.3, 1.4]), and early term birth (aRR 1.1, 95% CI [1.1, 1.2]). There was no effect modification of the overall association by race/ethnicity or insurance status. COVID-19 diagnosis was associated with elevated risk of PTB in people with hypertension, diabetes, and/or obesity. INTERPRETATION: In a large population-based study, COVID-19 diagnosis increased the risk of VPTB, PTB, and early term birth, particularly among people with medical comorbidities. Considering increased circulation of COVID-19 variants, preventative measures, including vaccination, should be prioritized for birthing persons. FUNDING: UCSF-Kaiser Department of Research Building Interdisciplinary Research Careers in Women's Health Program (BIRCWH) National Institute of Child Health and Human Development (NICHD) and the Office of Research on Women's Health (ORWH) [K12 HD052163] and the California Preterm Birth Initiative, funded by Marc and Lynn Benioff.

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.

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

Nationally representative data from the National Health and Nutrition Examination Survey (NHANES) indicate that over 65% of adults aged 51-70 years in the U.S. do not meet hydration criteria. They have hyponatremia (serum sodium < 135 mmol/L) and/or underhydration (serum sodium >145 mmol/L, spot urine volume <50 mL, and/or spot urine osmolality ≥500 mmol/kg). To explore potential public health implications of not meeting hydration criteria, data from the NHANES 2009-2012 and National Center for Health Statistics Linked Mortality Files for fasting adults aged 51-70 years (sample n = 1200) were used to determine if hyponatremia and/or underhydration were cross-sectionally associated with chronic health conditions and/or longitudinally associated with chronic disease mortality. Underhydration accounted for 97% of the population group not meeting hydration criteria. In weighted multivariable adjusted Poisson models, underhydration was significantly associated with increased prevalence of obesity, high waist circumference, insulin resistance, diabetes, low HDL, hypertension, and metabolic syndrome. Over 3-6 years of follow-up, 33 chronic disease deaths occurred in the sample, representing an estimated 1,084,144 deaths in the U.S. Alongside chronic health conditions, underhydration was a risk factor for an estimated 863,305 deaths. Independent of the chronic health conditions evaluated, underhydration was a risk factor for 128,107 deaths. In weighted multivariable Cox models, underhydration was associated with 4.21 times greater chronic disease mortality (95% CI: 1.29-13.78, p = 0.019). Zero chronic disease deaths were observed for people who met the hydration criteria and did not already have a chronic condition in 2009-2012. Further work should consider effects of underhydration on population health.

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.

Change in hydration indices associated with an increase in total water intake of more than 0.5 L/day, sustained over 4 weeks, in healthy young men with initial total water intake below 2 L/day.

This secondary data analysis addressed gaps in knowledge about effects of chronic water intake. Longitudinal data from the Adapt Study were used to describe effects of prescribing a sustained increase in water intake relative to baseline, for 4 weeks, on multiple indices of total body water (TBW) flux, regulation, distribution, and volume in five healthy, free-living, young men, with mean total water intake initially below 2 L/day. Indices were measured weekly. Within-person fixed effect models tested for significant changes in indices over time and associations between changes in indices. Agreement between indices was described. Mixed models tested if baseline between-person differences in hydration indices modified changes in indices over time. Body water flux: The half-life of water in the body decreased significantly. Body water regulation: Serum osmolality decreased significantly. Urine anti-diuretic hormone, sodium, potassium, and osmolality decreased significantly. Plasma aldosterone and serum sodium increased significantly. Body water distribution: No significant changes were observed. Body water volume: Saliva osmolality decreased significantly. Body weight increased significantly by a mean ± SEM of 1.8% ± 0.5% from baseline over 4 weeks. Changes in indices were significantly inter-correlated. Agreement between indices changed over 4 weeks. Baseline saliva osmolality significantly modified responses to chronic water intake. The results motivate hypotheses for future studies: Chronic TBW deficit occurs in healthy individuals under daily life conditions and increases chronic disease risk; Sustained higher water intake restores TBW through gradual isotonic retention of potassium and/or sodium; Saliva osmolality is a sensitive and specific index of chronic hydration status.

A Health Equity Problem for Low Income Children: Diet Flexibility Requires Physician Authorization.

USDA programs, such as the Child and Adult Care Food Program (CACFP), School Breakfast Program (SBP), and/or National School Lunch Program (NSLP), enable child care centers and schools to provide free and reduced price meals, daily, to millions of low income children. Despite intention to equalize opportunity for every child to have a healthy diet, USDA program rules may be contributing to child obesity disparities and health inequity. USDA program rules require child care centers and schools to provide meals that include a specified number of servings of particular types of foods and beverages. The rules are designed for the average, healthy weight child to maintain weight and growth. They are not designed for the underweight child to gain weight, obese child to normalize weight, or pre-diabetic child to avoid incident diabetes. The rules allow for only one meal pattern and volume, as opposed to a flexible spectrum of meal patterns and portion sizes. Parents of children who participate in the CACFP, SBP, and/or NSLP do not have control over the amount or composition of the subsidized meals. Parents of overweight, obese, or diabetic children who participate in the subsidized meal programs can request dietary change, special meals or accommodations to address their child's health status, but child care providers and schools are not required to comply with the request unless a licensed physician signs a "Medical statement to request special meals and/or accommodations". Although physicians are the only group authorized to change the foods, beverages, and portion sizes served daily to low income children, they are not doing so. Over the past three years, despite an overweight and obesity prevalence of 30% in San Francisco child care centers serving low income children, zero medical statements were filed to request special meals or accommodations to alter daily meals in order to prevent obesity, treat obesity, or prevent postprandial hyperglycemia. Low income children have systematically less dietary flexibility than higher income children, because of reliance on free or reduced-price meals, federal food program policy, and lack of awareness that only physicians have authority to alter the composition of subsidized meals in child care centers and schools. Compared with higher income children, low income children do not have equal opportunity to change their daily dietary intake to balance energy requirements.

Plasma hypertonicity: another marker of frailty?

OBJECTIVES: To determine whether plasma hypertonicity might be a marker of early frailty, this study tested the associations between plasma hypertonicity, incident disability, and mortality in nondisabled older adults. DESIGN: Longitudinal, observational study. SETTING: Community-based. PARTICIPANTS: Older adults (> or =70), who reported no disability and gave blood in the 1992 Duke Established Populations for Epidemiologic Studies of the Elderly survey (n=705), were re-interviewed in 1996 for functional status (n=561) and followed for all deaths up to January 1, 2000. MEASUREMENTS: Plasma tonicity was estimated from plasma glucose, sodium, and potassium measures and used to classify subjects as normo- (285-294 mOsm/L) or hypertonic (> or =300 mOsm/L). Disability was defined as any impairment on the Rosow-Breslau, activity of daily living (ADL), and instrumental activity of daily living (IADL) scales. The relative risk (RR) of any new disability and relative hazard of death associated with hypertonicity were estimated using logistic regression models and Cox proportional hazards models, respectively. All models were controlled for age, sex, race, weight status, current smoking, activity level, plasma blood urea nitrogen and creatinine, cognitive impairment, depression, and chronic disease status. To determine whether observed effects were attributable to plasma glucose alone, all models were repeated on a subsample of nondiabetic, normoglycemic subjects. RESULTS: Plasma hypertonicity (observed in 15% of subjects) was associated with increased risk of new Rosow-Breslau (RR=2.1, 95% confidence interval (CI)=1.2-3.6), IADL (RR=2.3, 95% CI=1.2-4.3), and ADL (RR=2.7 95% CI=1.3-5.6) disability by 1996 and mortality by 2000 (RR=1.4, 95% CI=1.0-1.9). Results were similar for the normoglycemic subgroup (ADL: RR=2.9, 95% CI=1.0-8.0; IADL: RR=2.5, 95% CI=1.0-6.3; Rosow-Breslau: RR=1.8, 95% CI=0.8-3.9; mortality: RR=1.5, 95% CI=0.9-2.3). CONCLUSION: Plasma hypertonicity may be a marker of early frailty. It was prevalent in this sample of nondisabled community-dwelling older adults and predicted incident disability and mortality. Further research to identify its determinants and consequences may help inform interventions against frailty.

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

OBJECTIVE: The qualitative recommendation to 'drink water instead of caloric beverages' may facilitate pediatric obesity treatment by lowering total energy intake. The quantitative recommendation to 'drink enough water to dilute urine' might further facilitate weight loss by increasing fat oxidation via cell hydration-mediated changes in insulin. METHODS: This 8 week randomized intervention tested whether both qualitative-plus-quantitative (QQ) drinking water recommendations result in more weight loss than the qualitative recommendation alone (Q) in 25 children (9-12y) with body mass index at or above the 85th Percentile, given a reduced glycemic diet and usual physical activity. Random urine osmolality, saliva insulin, and body weight were assessed weekly. Mixed models explored if insulin mediated an effect of urine osmolality on weight loss. RESULTS: In intention-to-treat analyses, QQ and Q participants did not differ significantly with respect to level of urine osmolality, saliva insulin, or weight loss. Only 4 out of 16 QQ participants complied with instruction to drink enough water to dilute urine, however. In completers analyses, the compliant QQ participants, who diluted urine osmolality from 910 ± 161 mmol/kg at baseline to below 500 mmol/kg over time (8 week mean±SE: 450 ± 67 mmol/kg), had significantly lower saliva insulin over time (8 week mean±SE: 13 ± 8 pmol/l vs. 22 ± 4 pmol/l) and greater weight loss (mean ± SE: -3.3 ± 0.7kg vs. -2.0 ± 0.5 kg) than compliant Q participants (7 out of 9 participants) who maintained elevated urine osmolality over time (8- week mean±SE: 888 ± 41 mmol/kg). Urine osmolality below 500 mmol/kg was significantly associated with weight loss. Change in saliva insulin partially explained the association. CONCLUSIONS: QQ recommendations may increase weight loss for those able to dilute urine. Work is warranted to pursue cell hydration effects of drinking water for pediatric obesity treatment.

RBC deformability and amino acid concentrations after hypo-osmotic challenge may reflect chronic cell hydration status in healthy young men.

Biomarkers of chronic cell hydration status are needed to determine whether chronic hyperosmotic stress increases chronic disease risk in population-representative samples. In vitro, cells adapt to chronic hyperosmotic stress by upregulating protein breakdown to counter the osmotic gradient with higher intracellular amino acid concentrations. If cells are subsequently exposed to hypo-osmotic conditions, the adaptation results in excess cell swelling and/or efflux of free amino acids. This study explored whether increased red blood cell (RBC) swelling and/or plasma or urine amino acid concentrations after hypo-osmotic challenge might be informative about relative chronic hyperosmotic stress in free-living men. Five healthy men (20-25 years) with baseline total water intake below 2 L/day participated in an 8-week clinical study: four 2-week periods in a U-shaped A-B-C-A design. Intake of drinking water was increased by +0.8 ± 0.3 L/day in period 2, and +1.5 ± 0.3 L/day in period 3, and returned to baseline intake (0.4 ± 0.2 L/day) in period 4. Each week, fasting blood and urine were collected after a 750 mL bolus of drinking water, following overnight water restriction. The periods of higher water intake were associated with significant decreases in RBC deformability (index of cell swelling), plasma histidine, urine arginine, and urine glutamic acid. After 4 weeks of higher water intake, four out of five participants had ½ maximal RBC deformability below 400 mmol/kg; plasma histidine below 100 µmol/L; and/or undetectable urine arginine and urine glutamic acid concentrations. Work is warranted to pursue RBC deformability and amino acid concentrations after hypo-osmotic challenge as possible biomarkers of chronic cell hydration.

Drinking water is associated with weight loss in overweight dieting women independent of diet and activity.

BACKGROUND: Data from short-term experiments suggest that drinking water may promote weight loss by lowering total energy intake and/or altering metabolism. The long-term effects of drinking water on change in body weight and composition are unknown, however. OBJECTIVE: This study tested for associations between absolute and relative increases in drinking water and weight loss over 12 months. METHODS AND PROCEDURES: Secondary analyses were conducted on data from the Stanford A TO Z weight loss intervention on 173 premenopausal overweight women (aged 25-50 years) who reported <1 l/day drinking water at baseline. Diet, physical activity, body weight, percent body fat (dual-energy X-ray absorptiometry), and waist circumference were assessed at baseline, 2, 6, and 12 months. At each time point, mean daily intakes of drinking water, noncaloric, unsweetened caloric (e.g., 100% fruit juice, milk) and sweetened caloric beverages, and food energy and nutrients were estimated using three unannounced 24-h diet recalls. Beverage intake was expressed in absolute (g) and relative terms (% of beverages). Mixed models were used to test for effects of absolute and relative increases in drinking water on changes in weight and body composition, controlling for baseline status, diet group, and changes in other beverage intake, the amount and composition of foods consumed and physical activity. RESULTS: Absolute and relative increases in drinking water were associated with significant loss of body weight and fat over time, independent of covariates. DISCUSSION: The results suggest that drinking water may promote weight loss in overweight dieting women.

Replacing sweetened caloric beverages with drinking water is associated with lower energy intake.

OBJECTIVE: Reduced intake of sweetened caloric beverages (SCBs) is recommended to lower total energy intake. Replacing SCBs with non-caloric diet beverages does not automatically lower energy intake, however. Compensatory increases in other food or beverages reportedly negate benefits of diet beverages. The purpose of this study was to evaluate drinking water as an alternative to SCBs. RESEARCH METHODS AND PROCEDURES: Secondary analysis of data from the Stanford A TO Z intervention evaluated change in beverage pattern and total energy intake in 118 overweight women (25 to 50 years) who regularly consumed SCBs (>12 ounces/d) at baseline. At baseline and 2, 6, and 12 months, mean daily beverage intake (SCBs, drinking water, non-caloric diet beverages, and nutritious caloric beverages), food composition (macronutrient, water, and fiber content), and total energy intake were estimated using three 24-hour diet recalls. Beverage intake was expressed in relative terms (percentage of beverages). RESULTS: In fixed effects models that controlled for total beverage intake, non-caloric and nutritious caloric beverage intake (percentage of beverages), food composition, and energy expenditure [metabolic equivalent (MET)], replacing SCBs with drinking water was associated with significant decreases in total energy intake that were sustained over time. The caloric deficit attributable to replacing SCBs with water was not negated by compensatory increases in other food or beverages. Replacing all SCBs with drinking water was associated with a predicted mean decrease in total energy of 200 kcal/d over 12 months. DISCUSSION: The results suggest that replacing SCBs with drinking water can help lower total energy intake in overweight consumers of SCBs motivated to diet.