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1.
Sodium/glucose cotransporter 2 and renoprotection: From the perspective of energy regulation and water conservation.
Kitada, K, Kidoguchi, S, Nakano, D, Nishiyama, A
Journal of pharmacological sciences. 2021;(3):245-250
Abstract
Sodium/glucose cotransporter 2 (SGLT2) is a renal low-affinity high-capacity sodium/glucose cotransporter expressed in the apical membrane of the early segment of proximal tubules. SGLT2 reabsorbs filtered glucose in the kidney, and its inhibitors represent a new class of oral medications used for type 2 diabetes mellitus, which act by increasing glucose and sodium excretion in urine, thereby reducing blood glucose levels. However, clinical trials showed marked improvement of renal outcomes, even in nondiabetic kidney diseases, although the underlying mechanism of this renoprotective effect is unclear. We showed that long-term excretion of salt by the kidneys, which predisposes to osmotic diuresis and water loss, induces a systemic body response for water conservation. The energy-intensive nature of water conservation leads to a reprioritization of systemic body energy metabolism. According to current data, use of SGLT2 inhibitors may result in similar reprioritization of energy metabolism to prevent dehydration. In this review article, we discuss the beneficial effects of SGLT2 inhibition from the perspective of energy metabolism and water conservation.
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Reviewing the current methods of assessing hydration in athletes.
Barley, OR, Chapman, DW, Abbiss, CR
Journal of the International Society of Sports Nutrition. 2020;(1):52
Abstract
BACKGROUND Despite a substantial body of research, no clear best practice guidelines exist for the assessment of hydration in athletes. Body water is stored in and shifted between different sites throughout the body complicating hydration assessment. This review seeks to highlight the unique strengths and limitations of various hydration assessment methods described in the literature as well as providing best practice guidelines. MAIN BODY There is a plethora of methods that range in validity and reliability, including complicated and invasive methods (i.e. neutron activation analysis and stable isotope dilution), to moderately invasive blood, urine and salivary variables, progressing to non-invasive metrics such as tear osmolality, body mass, bioimpedance analysis, and sensation of thirst. Any single assessment of hydration status is problematic. Instead, the recommended approach is to use a combination, which have complementary strengths, which increase accuracy and validity. If methods such as salivary variables, urine colour, vital signs and sensation of thirst are utilised in isolation, great care must be taken due to their lack of sensitivity, reliability and/or accuracy. Detailed assessments such as neutron activation and stable isotope dilution analysis are highly accurate but expensive, with significant time delays due to data analysis providing little potential for immediate action. While alternative variables such as hormonal and electrolyte concentration, bioimpedance and tear osmolality require further research to determine their validity and reliability before inclusion into any test battery. CONCLUSION To improve best practice additional comprehensive research is required to further the scientific understanding of evaluating hydration status.
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3.
Hydration Status and Cardiovascular Function.
Watso, JC, Farquhar, WB
Nutrients. 2019;(8)
Abstract
Hypohydration, defined as a state of low body water, increases thirst sensations, arginine vasopressin release, and elicits renin-angiotensin-aldosterone system activation to replenish intra- and extra-cellular fluid stores. Hypohydration impairs mental and physical performance, but new evidence suggests hypohydration may also have deleterious effects on cardiovascular health. This is alarming because cardiovascular disease is the leading cause of death in the United States. Observational studies have linked habitual low water intake with increased future risk for adverse cardiovascular events. While it is currently unclear how chronic reductions in water intake may predispose individuals to greater future risk for adverse cardiovascular events, there is evidence that acute hypohydration impairs vascular function and blood pressure (BP) regulation. Specifically, acute hypohydration may reduce endothelial function, increase sympathetic nervous system activity, and worsen orthostatic tolerance. Therefore, the purpose of this review is to present the currently available evidence linking acute hypohydration with altered vascular function and BP regulation.
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4.
[Human Body Water Composition Measurement:Methods and Clinical Application].
Zhou, SG, Chen, W
Zhongguo yi xue ke xue yuan xue bao. Acta Academiae Medicinae Sinicae. 2018;(5):603-609
Abstract
Being the largest single component of the human body,water is essential for life. Disease can lead to salt and water imbalance, and it is particularly important to measure the content and distribution of water in body. The current body water measurement methods are still not mature,and it's even hard to measure extracellular and intracellular water. Isotope dilution method(ID),bioelectrical impedance analysis(BIA),skinfold thickness measurement,and resonant cavity perturbation(RCP)are the commonly used methods for measuring human body water composition. This paper analyzes the advantages and disadvantages of these methods and concludes that all these four methods can be used to measure total body water;more specifically,ID and BIA can measure extracellular water and intracellular water,whereas BIA is more suitable for clinical applications such as monitoring of fluid balance,guiding of fluid management,assessment of lymphedema and nutritional risk,and management of obesity. Body water measurement will play more important roles in diagnosis,prevention,treatment,and prognosis of diseases.
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5.
Water Intake, Water Balance, and the Elusive Daily Water Requirement.
Armstrong, LE, Johnson, EC
Nutrients. 2018;(12)
Abstract
Water is essential for metabolism, substrate transport across membranes, cellular homeostasis, temperature regulation, and circulatory function. Although nutritional and physiological research teams and professional organizations have described the daily total water intakes (TWI, L/24h) and Adequate Intakes (AI) of children, women, and men, there is no widespread consensus regarding the human water requirements of different demographic groups. These requirements remain undefined because of the dynamic complexity inherent in the human water regulatory network, which involves the central nervous system and several organ systems, as well as large inter-individual differences. The present review analyzes published evidence that is relevant to these issues and presents a novel approach to assessing the daily water requirements of individuals in all sex and life-stage groups, as an alternative to AI values based on survey data. This empirical method focuses on the intensity of a specific neuroendocrine response (e.g., plasma arginine vasopressin (AVP) concentration) employed by the brain to regulate total body water volume and concentration. We consider this autonomically-controlled neuroendocrine response to be an inherent hydration biomarker and one means by which the brain maintains good health and optimal function. We also propose that this individualized method defines the elusive state of euhydration (i.e., water balance) and distinguishes it from hypohydration. Using plasma AVP concentration to analyze multiple published data sets that included both men and women, we determined that a mild neuroendocrine defense of body water commences when TWI is ˂1.8 L/24h, that 19⁻71% of adults in various countries consume less than this TWI each day, and consuming less than the 24-h water AI may influence the risk of dysfunctional metabolism and chronic diseases.
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6.
Myths and methodologies: Making sense of exercise mass and water balance.
Cheuvront, SN, Montain, SJ
Experimental physiology. 2017;(9):1047-1053
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Abstract
What is the topic of this review? There is a need to revisit the basic principles of exercise mass and water balance, the use of common equations and the practice of interpreting outcomes. What advances does it highlight? We propose use of the following equation as a way of simplifying exercise mass and water balance calculations in conditions where food is not consumed and waste is not excreted: ∆body mass - 0.20 g/kcal-1 = ∆body water. The relative efficacy of exercise drinking behaviours can be judged using the following equation: percentage dehydration = [(∆body mass - 0.20 g kcal-1 )/starting body mass] × 100. Changes in body mass occur because of flux in liquids, solids and gases. This knowledge is crucial for understanding metabolism, health and human water needs. In exercise science, corrections to observed changes in body mass to estimate water balance are inconsistently applied and often misinterpreted, particularly after prolonged exercise. Although acute body mass losses in response to exercise can represent a close surrogate for body water losses, the discordance between mass and water balance equivalence becomes increasingly inaccurate as more and more energy is expended. The purpose of this paper is briefly to clarify the roles that respiratory water loss, gas exchange and metabolic water production play in the correction of body mass changes for fluid balance determinations during prolonged exercise. Computations do not include waters of association with glycogen because any movement of water among body water compartments contributes nothing to water or mass flux from the body. Estimates of sweat loss from changes in body mass should adjust for non-sweat losses when possible. We propose use of the following equation as a way of simplifying the study of exercise mass and water balance: ∆body mass - 0.20 g kcal-1 = ∆body water. This equation directly controls for the influence of energy expenditure on body mass balance and the approximate offsetting equivalence of respiratory water loss and metabolic water production on body water balance. The relative efficacy of exercise drinking behaviours can be judged using the following equation: percentage dehydration = [(∆body mass - 0.20 g kcal-1 )/starting body mass] × 100.
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Why choose high volume online post-dilution hemodiafiltration?
Basile, C, Davenport, A, Blankestijn, PJ
Journal of nephrology. 2017;(2):181-186
Abstract
The mortality rate of patients on maintenance dialysis remains alarmingly high, at approximately 15-20 % per year. Increasing dialyzer urea clearance has not been shown to improve survival and hence interest has shifted towards convective therapies, such as hemodiafiltration (HDF) which can remove middle molecular weight uremic toxins, which have been suggested to increase mortality in patients with end-stage kidney disease. During the last few years, four large prospective randomized controlled trials (RCTs) have been conducted in different European countries to compare survival outcomes in prevalent patients receiving conventional hemodialysis with online post-dilution HDF (OL HDF). Furthermore, a pooled individual participant data analysis from four RCTs was performed and four large meta-analyses on convective therapies have been published in the last 2 years. Taken together, these studies support the conclusion that high volume post-dilution OL HDF is associated with improved overall survival. This advantage results predominantly from a lower cardiovascular mortality, possibly due to better preservation of left ventricle mass and function. Improved intra-dialytic blood pressure stability may contribute to the beneficial effect of high volume post-dilution OL HDF on survival. The beneficial effect is not restricted to selected subgroups, such as age, comorbidity or dialysis vintage. There is no compelling evidence that high volume post-dilution OL HDF reduces mortality by improvements in traditional and non-traditional risk factors. There are still no studies or case reports published describing adverse clinical outcomes in more than 20 years of HDF clinical experience. In conclusion, most of the available data support the choice of high volume post-dilution HDF over the current dialysis techniques. However, considering that we live in the era of evidence-based medicine, the evidence supporting the superiority of high volume post-dilution OL HDF in comparison to hemodialysis is still missing: in fact, a new RCT targeting different convection volumes would be needed to definitively examine the dose-response effect shown in previous studies.
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CORP: Improving the status quo for measuring whole body sweat losses.
Cheuvront, SN, Kenefick, RW
Journal of applied physiology (Bethesda, Md. : 1985). 2017;(3):632-636
Abstract
The measurement of whole body sweat losses (WBSL) is important to the study of body heat balance, body water balance, establishing guidelines for water and electrolyte consumption, and the study of metabolism and health. In principal, WBSL is measured by an acute change in body mass (ΔBM) in response to a thermoregulatory sweating stimulus. In this Cores of Reproducibility in Physiology (CORP) review, we revisit several basic, but rarely discussed, assumptions important to WBSL research, including the common equivalences: mass = weight = water = sweat. Sources of large potential measurement errors are also discussed, as are best practices for avoiding them. The goal of this CORP review is to ultimately improve the accuracy, reproducibility, and application of WBSL research.
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Water balance in the fetus and neonate.
Lindower, JB
Seminars in fetal & neonatal medicine. 2017;(2):71-75
Abstract
Fetal water balance is dependent prenatally on the placental transfer of water from maternal to fetal circulation. Adequate amniotic fluid volume is one indicator of stable fetal status and development. Excessive or less than expected amniotic fluid volume may be a precursor to postnatal morbidity and mortality. Postnatal transition is marked by predictable changes in body water including contraction of extracellular volume and insensible fluid loss, primarily across the skin barrier. The degree to which these occur is determined by gestational and postnatal age. Neonatal complications and clinical conditions associated with either retention or excessive loss of body water can occur. Fluid therapy in the neonatal intensive care unit may be guided using three clinical indicators: change in body weight, serum sodium concentration, and urine output.
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Effects of acute and chronic hypohydration on kidney health and function.
Feehally, J, Khosravi, M
Nutrition reviews. 2015;:110-9
Abstract
The kidneys play a critical role in the homeostasis of body fluid tonicity and effective circulating volume. Renal homeostatic mechanisms are frequently challenged in acutely ill people. Fluid depletion causing hypovolemia may result in renal hypoperfusion that, if left untreated, may lead to acute kidney failure. Some populations, notably older people and neonates, are less tolerant of extremes in fluid loading and deprivation, similar to those with established chronic kidney disease. Risk of kidney injury during fluid depletion is increased by medications including diuretics, nonsteroidal antiinflammatory drugs, and renin-angiotensin system blockers. There is no consistent evidence indicating that lower-than-average fluid intake can cause chronic kidney disease, nor accelerate progression of established kidney disease. Increasing consumption of sugar-containing beverages is, however, a major concern for kidney health as a precursor of obesity and diabetes. There is no evidence that high dietary protein intake can cause chronic kidney disease, nor accelerate progression of established kidney disease. Idiosyncratic, adverse renal responses have been described with creatine supplements. There are only a few clinical conditions for which high fluid intake should be considered. These include recurrent kidney stones or urinary tract infections and, possibly, polycystic kidney disease.