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1.
Anhydrobiosis: Inside yeast cells.
Rapoport, A, Golovina, EA, Gervais, P, Dupont, S, Beney, L
Biotechnology advances. 2019;(1):51-67
Abstract
Under natural conditions yeast cells as well as other microorganisms are regularly subjected to the influence of severe drought, which leads to their serious dehydration. The dry seasons are then changed by rains and there is a restoration of normal water potential inside the cells. To survive such seasonal changes a lot of vegetative microbial cells, which belong to various genera and species, may be able to enter into a state of anhydrobiosis, in which their metabolism is temporarily and reversibly suspended or delayed. This evolutionarily developed adaptation to extreme conditions of the environment is widely used for practical goals - for conservation of microorganisms in collections, for maintenance and long storage of different important strain-producers and for other various biotechnological purposes. This current review presents the most important data obtained mainly in the studies of the structural and functional changes in yeast cells during dehydration. It describes the changes of the main organelles of eukaryotic cells and their role in cell survival in a dry state. The review provides information regarding the role of water in the structure and functions of biological macromolecules and membranes. Some important intracellular protective reactions of eukaryotic organisms, which were revealed in these studies and may have more general importance, are also discussed. The results of the studies of yeast anhydrobiosis summarized in the review show the possibilities of improving the conservation and long-term storage of various microorganisms and of increasing the quality of industrially produced dry microbial preparations.
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2.
Does Hypohydration Really Impair Endurance Performance? Methodological Considerations for Interpreting Hydration Research.
James, LJ, Funnell, MP, James, RM, Mears, SA
Sports medicine (Auckland, N.Z.). 2019;(Suppl 2):103-114
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Abstract
The impact of alterations in hydration status on human physiology and performance responses during exercise is one of the oldest research topics in sport and exercise nutrition. This body of work has mainly focussed on the impact of reduced body water stores (i.e. hypohydration) on these outcomes, on the whole demonstrating that hypohydration impairs endurance performance, likely via detrimental effects on a number of physiological functions. However, an important consideration, that has received little attention, is the methods that have traditionally been used to investigate how hypohydration affects exercise outcomes, as those used may confound the results of many studies. There are two main methodological limitations in much of the published literature that perhaps make the results of studies investigating performance outcomes difficult to interpret. First, subjects involved in studies are generally not blinded to the intervention taking place (i.e. they know what their hydration status is), which may introduce expectancy effects. Second, most of the methods used to induce hypohydration are both uncomfortable and unfamiliar to the subjects, meaning that alterations in performance may be caused by this discomfort, rather than hypohydration per se. This review discusses these methodological considerations and provides an overview of the small body of recent work that has attempted to correct some of these methodological issues. On balance, these recent blinded hydration studies suggest hypohydration equivalent to 2-3% body mass decreases endurance cycling performance in the heat, at least when no/little fluid is ingested.
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3.
Short sleep duration is associated with inadequate hydration: cross-cultural evidence from US and Chinese adults.
Rosinger, AY, Chang, AM, Buxton, OM, Li, J, Wu, S, Gao, X
Sleep. 2019;(2)
Abstract
STUDY OBJECTIVES Short and long sleep durations are linked to reduced kidney function, but little research has examined how sleep is associated with hydration status. Our aim was to assess the relationship between sleep duration and urinary hydration biomarkers among adults in a cross-cultural context. METHODS Three samples of adults aged ≥20 years were analyzed: 2007-2008 National Health and Nutrition Examination Survey (NHANES; n = 4680), 2009-2012 NHANES (n = 9559), and 2012 cross-sectional wave of the Chinese Kailuan Study (n = 11903), excluding pregnant women and adults with failing kidneys. We estimated multiple linear regression models between self-reported usual night-time sleep duration (<6, 6, 7, 8 (reference), and ≥9 hr/day) and urine specific gravity (Usg) and urine osmolality (Uosm) as continuous variables and logistic regression models dichotomized as inadequate hydration (>1.020 g/mL; >831 mOsm/kg). In primary analyses, we estimated models excluding diabetes and diuretic medications for healthier subpopulations (NHANES, n = 11353; Kailuan, n = 8766). RESULTS In the healthier NHANES subset, 6 hr was associated with significantly higher Usg and odds of inadequate hydration (adjusted OR: 1.59, 95% CI: 1.25, 2.03) compared with 8 hr. Regression results were mixed using Uosm, but in the same direction as Usg. Among Chinese adults, short sleep duration (<6 and 6 hr) was associated with Usg and higher likelihood of inadequate hydration (6 hr adjusted OR: 1.42, 95% CI: 1.26, 1.60). No consistent association was found with sleeping ≥9 hr. CONCLUSIONS Short sleep duration was associated with higher odds of inadequate hydration in US and Chinese adults relative to sleeping 8 hr.
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4.
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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5.
Heat, Hydration and the Human Brain, Heart and Skeletal Muscles.
Trangmar, SJ, González-Alonso, J
Sports medicine (Auckland, N.Z.). 2019;(Suppl 1):69-85
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Abstract
People undertaking prolonged vigorous exercise experience substantial bodily fluid losses due to thermoregulatory sweating. If these fluid losses are not replaced, endurance capacity may be impaired in association with a myriad of alterations in physiological function, including hyperthermia, hyperventilation, cardiovascular strain with reductions in brain, skeletal muscle and skin blood perfusion, greater reliance on muscle glycogen and cellular metabolism, alterations in neural activity and, in some conditions, compromised muscle metabolism and aerobic capacity. The physiological strain accompanying progressive exercise-induced dehydration to a level of ~ 4% of body mass loss can be attenuated or even prevented by: (1) ingesting fluids during exercise, (2) exercising in cold environments, and/or (3) working at intensities that require a small fraction of the overall body functional capacity. The impact of dehydration upon physiological function therefore depends on the functional demand evoked by exercise and environmental stress, as cardiac output, limb blood perfusion and muscle metabolism are stable or increase during small muscle mass exercise or resting conditions, but are impaired during whole-body moderate to intense exercise. Progressive dehydration is also associated with an accelerated drop in perfusion and oxygen supply to the human brain during submaximal and maximal endurance exercise. Yet their consequences on aerobic metabolism are greater in the exercising muscles because of the much smaller functional oxygen extraction reserve. This review describes how dehydration differentially impacts physiological function during exercise requiring low compared to high functional demand, with an emphasis on the responses of the human brain, heart and skeletal muscles.
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Influence of Sodium Citrate Supplementation after Dehydrating Exercise on Responses of Stress Hormones to Subsequent Endurance Cycling Time-Trial in the Heat.
Suvi, S, Mooses, M, Timpmann, S, Medijainen, L, Unt, E, Ööpik, V
Medicina (Kaunas, Lithuania). 2019;(4)
Abstract
Background and objectives: In temperate environments, acute orally induced metabolic alkalosis alleviates exercise stress, as reflected in attenuated stress hormone responses to relatively short-duration exercise bouts. However, it is unknown whether the same phenomenon occurs during prolonged exercise in the heat. This study was undertaken with aim to test the hypothesis that ingestion of an alkalizing substance (sodium citrate; CIT) after dehydrating exercise would decrease blood levels of stress hormones during subsequent 40 km cycling time-trial (TT) in the heat. Materials and Methods: Male non-heat-acclimated athletes (n = 20) lost 4% of body mass by exercising in the heat. Then, during a 16 h recovery period prior to TT in a warm environment (32 °C), participants ate the prescribed food and ingested CIT (600 mg·kg-1) or placebo (PLC) in a double-blind, randomized, crossover manner with 7 days between the two trials. Blood aldosterone, cortisol, prolactin and growth hormone concentrations were measured before and after TT. Results: Total work performed during TT was similar in the two trials (p = 0.716). In CIT compared to PLC trial, lower levels of aldosterone occurred before (72%) and after (39%) TT (p ˂ 0.001), and acute response of aldosterone to TT was blunted (29%, p ˂ 0.001). Lower cortisol levels in CIT than in PLC trial occurred before (13%, p = 0.039) and after TT (14%, p = 0.001), but there were no between-trial differences in the acute responses of cortisol, prolactin or growth hormone to TT, or in concentrations of prolactin and growth hormone before or after TT (in all cases p > 0.05). Conclusions: Reduced aldosterone and cortisol levels after TT and blunted acute response of aldosterone to TT indicate that CIT ingestion during recovery after dehydrating exercise may alleviate stress during the next hard endurance cycling bout in the heat.
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Mild hypohydration impairs cycle ergometry performance in the heat: A blinded study.
Adams, JD, Scott, DM, Brand, NA, Suh, HG, Seal, AD, McDermott, BP, Ganio, MS, Kavouras, SA
Scandinavian journal of medicine & science in sports. 2019;(5):686-695
Abstract
The aim of the present study was to observe the effect of mild hypohydration on exercise performance with subjects blinded to their hydration status. Eleven male cyclists (weight 75.8 ± 6.4 kg, VO2peak : 64.9 ± 5.6 mL/kg/min, body fat: 12.0 ± 5.8%, Powermax : 409 ± 40 W) performed three sets of criterium-like cycling, consisting of 20-minute steady-state cycling (50% peak power output), each followed by a 5-km time trial at 3% grade. Following a familiarization trial, subjects completed the experimental trials, in counter-balanced fashion, on two separate occasions in dry heat (30°C, 30% rh) either hypohydrated (HYP) or euhydrated (EUH). In both trials, subjects ingested 25 mL of water every 5 minutes during the steady-state and every 1 km of the 5-km time trials. In the EUH trial, sweat losses were fully replaced via intravenous infusion of isotonic saline, while in the HYP trial, a sham IV was instrumented. Following the exercise protocol, the subjects' bodyweight was changed by -0.1 ± 0.1% and -1.8 ± 0.2% for the EUH and HYP trial, respectively (P < 0.05). During the second and third time trials, subjects averaged higher power output (309 ± 5 and 306 ± 5 W) and faster cycling speed (27.5 ± 3.0 and 27.2 ± 3.1 km/h) in the EUH trial compared to the HYP trial (Power: 287 ± 4 and 276 ± 5 W, Speed: 26.2 ± 2.9 and 25.5 ± 3.3 km/h, all P < 0.05). Core temperature (Tre ) was higher in the HYP trial throughout the third steady-state and 5-km time trial (P < 0.05). These data suggest that mild hypohydration, even when subjects were unaware of their hydration state, impaired cycle ergometry performance in the heat probably due to greater thermoregulatory strain.
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A randomized trial to assess beverage hydration index in healthy older adults.
Clarke, MM, Stanhewicz, AE, Wolf, ST, Cheuvront, SN, Kenefick, RW, Kenney, WL
The American journal of clinical nutrition. 2019;(6):1640-1647
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Abstract
BACKGROUND The beverage hydration index (BHI) is a composite measure of fluid balance after consuming a test beverage relative to water. BHI is a relatively new measure that has been explored in young, but not yet older, adults. OBJECTIVE The aim of this study was to investigate potential differences in BHI between euhydrated younger and older adults after drinking 4 different commercial beverages. We hypothesized that 1) older subjects would remain in positive fluid balance longer than young subjects after ingestion of each test beverage due to decreased urinary excretion rates, 2) glucose (glu)- and amino acid (AA)-based hydration beverages with sodium would have a BHI greater than water in both groups, and 3) the traditional 2-h postingestion BHI may be inappropriate for older adults. METHODS On 5 separate visits, 12 young (23 ± 3 yr, 7 M/5F) and 12 older (67 ± 6 yr, 5 M/7F) subjects consumed 1 L of distilled water, G-20 (6% CHO, 20 mmol/L Na+), G-45 (2.5% CHO, 45 mmol/L Na+), AA-30 (5 AAs, 30 mmol/L Na+), or AA-60 (8 AAs, 60 mmol/L Na+) over 30 min. Blood and urine samples were collected before ingestion and at 0, 60, 120, 180, and 240 min postingestion with additional venous blood sampling at 5, 10, 15, and 30 min postingestion. RESULTS In young subjects, BHI increased with increasing beverage Na+ concentration, and AA-60 had the highest BHI (AA-60 = 1.24 ± 0.10 compared with water = 1.00, P = 0.01). For older subjects, BHI was highest in AA-30 (AA-30; 1.20 ± 0.13 compared with water, P < 0.01) and was still in flux beyond 2 h in AA-60 (P < 0.05). CONCLUSIONS Beverage Na+ content progressively increased BHI in young adults independent of glucose or AA content. For older adults, the AA-30 beverage had the highest BHI. A 4-h BHI may be more appropriate for older adults due to attenuated urine excretion rates. This trial was registered at clinicaltrials.gov as NCT03559101.
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Altered brain structure with preserved cortical motor activity after exertional hypohydration: a MRI study.
Tan, XR, Low, ICC, Stephenson, MC, Kok, T, Nolte, HW, Soong, TW, Lee, JKW
Journal of applied physiology (Bethesda, Md. : 1985). 2019;(1):157-167
Abstract
Hypohydration exceeding 2% body mass can impair endurance capacity. It is postulated that the brain could be perturbed by hypohydration, leading to impaired motor performance. We investigated the neural effects of hypohydration with magnetic resonance imaging (MRI). Ten men were dehydrated to approximately -3% body mass by running on a treadmill at 65% maximal oxygen consumption (V̇o2max) before drinking to replace either 100% [euhydration (EU)] or 0% [hypohydration (HH)] of fluid losses. MRI was performed before start of trial (baseline) and after rehydration phase (post) to evaluate brain structure, cerebral perfusion, and functional activity. Endurance capacity assessed with a time-to-exhaustion run at 75% V̇o2max was reduced with hypohydration (EU: 45.2 ± 9.3 min, HH: 38.4 ± 10.7 min; P = 0.033). Mean heart rates were comparable between trials (EU: 162 ± 5 beats/min, HH: 162 ± 4 beats/min; P = 0.605), but the rate of rise in rectal temperature was higher in HH trials (EU: 0.06 ± 0.01°C/min, HH: 0.07 ± 0.02°C/min; P < 0.01). In HH trials, a reduction in total brain volume (EU: +0.7 ± 0.6%, HH: -0.7 ± 0.9%) with expansion of ventricles (EU: -2.7 ± 1.6%, HH: +3.7 ± 3.3%) was observed, and vice versa in EU trials. Global and regional cerebral perfusion remained unchanged between conditions. Functional activation in the primary motor cortex in left hemisphere during a plantar-flexion task was similar between conditions (EU: +0.10 ± 1.30%, HH: -0.11 ± 0.31%; P = 0.637). Our findings demonstrate that with exertional hypohydration, brain volumes were altered but the motor-related functional activity was unperturbed. NEW & NOTEWORTHY Dehydration occurs rapidly during prolonged or intensive physical activity, leading to hypohydration if fluid replenishment is insufficient to replace sweat losses. Altered hydration status poses an osmotic challenge for the brain, leading to transient fluctuations in brain tissue and ventricle volumes. Therefore, the amount of fluid ingestion during exercise plays a critical role in preserving the integrity of brain architecture. These structural changes, however, did not translate directly to motor functional deficits in a simple motor task.
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Considerations for ultra-endurance activities: part 2 - hydration.
Hoffman, MD, Stellingwerff, T, Costa, RJS
Research in sports medicine (Print). 2019;(2):182-194
Abstract
It is not unusual for those participating in ultra-endurance (> 4 hr) events to develop varying degrees of either hypohydration or hyperhydration. Yet, it is important for ultra-endurance athletes to avoid the performance limiting and potentially fatal consequences of these conditions. During short periods of exercise (< 1 hr), trivial effects on the relationship between body mass change and hydration status result from body mass loss due to oxidation of endogenous fuel stores, and water supporting the intravascular volume being generated from endogenous fuel oxidation and released with glycogen oxidation. However, these effects have meaningful implications during prolonged exercise. In fact, body mass loses well over 2% may be required during some ultra-endurance activities to avoid hyperhydration. Therefore, the typical hydration guidelines to avoid more than 2% body mass loss do not apply in ultra-endurance activities and can potentially result in hyperhydration. Fortunately, achieving the balance of proper hydration during ultra-endurance activities need not be complicated and has been well demonstrated to generally be achieved by simply drinking to thirst and avoiding excessive sodium supplementation with intention of replacing all sodium losses during the exercise.