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1.
Up in the Air: Evidence of Dehydration Risk and Long-Haul Flight on Athletic Performance.
Zubac, D, Buoite Stella, A, Morrison, SA
Nutrients. 2020;(9)
Abstract
The microclimate of an airline cabin consists of dry, recirculated, and cool air, which is maintained at lower pressure than that found at sea level. Being exposed to this distinctive, encapsulated environment for prolonged durations, together with the short-term chair-rest immobilization that occurs during long-haul flights, can trigger distinct and detrimental reactions to the human body. There is evidence that long-haul flights promote fluid shifts to the lower extremity and induce changes in blood viscosity which may accelerate dehydration, possibly compromising an athlete's potential for success upon arrival at their destination. Surprisingly, and despite several recent systematic reviews investigating the effects of jet lag and transmeridian travel on human physiology, there has been no systematic effort to address to what extent hypohydration is a (health, performance) risk to travelers embarking on long journeys. This narrative review summarizes the rationale and evidence for why the combination of fluid balance and long-haul flight remains a critically overlooked issue for traveling persons, be it for health, leisure, business, or in a sporting context. Upon review, there are few studies which have been conducted on actual traveling athletes, and those that have provide no real evidence of how the incidence rate, magnitude, or duration of acute dehydration may affect the general health or performance of elite athletes.
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2.
Does Dehydration Affect the Adaptations of Plasma Volume, Heart Rate, Internal Body Temperature, and Sweat Rate During the Induction Phase of Heat Acclimation?
Sekiguchi, Y, Filep, EM, Benjamin, CL, Casa, DJ, DiStefano, LJ
Journal of sport rehabilitation. 2020;(6):847-850
Abstract
Clinical Scenario: Exercise in the heat can lead to performance decrements and increase the risk of heat illness. Heat acclimation refers to the systematic and gradual increase in exercise in a controlled, laboratory environment. Increased duration and intensity of exercise in the heat positively affects physiological responses, such as higher sweat rate, plasma volume expansion, decreased heart rate, and lower internal body temperature. Many heat acclimation studies have examined the hydration status of the subjects exercising in the heat. Some of the physiological responses that are desired to elicit heat acclimation (ie, higher heart rate and internal body temperature) are exacerbated in a dehydrated state. Thus, euhydration (optimal hydration) and dehydration trials during heat acclimation induction have been conducted to determine if there are additional benefits to dehydrated exercise trials on physiological adaptations. However, there is still much debate over hydration status and its effect on heat acclimation. Clinical Question: Does dehydration affect the adaptations of plasma volume, heart rate, internal body temperature, skin temperature, and sweat rate during the induction phase of heat acclimation? Summary of Findings: There were no observed differences in plasma volume, internal body temperature, and skin temperature following heat acclimation in this critically appraised topic. One study found an increase in sweat rate and another study indicated greater changes in heart rate following heat acclimation with dehydration. Aside from these findings, all 4 trials did not observe statistically significant differences in euhydrated and dehydrated heat acclimation trials. Clinical Bottom Line: There is minimal evidence to suggest that hydration status affects heat acclimation induction. In the studies that met the inclusion criteria, there were no differences in plasma volume concentrations, internal body temperature, and skin temperature. Strength of Recommendation: Based on the Oxford Centre for Evidence-Based Medicine Scale, Level 2 evidence exists.
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3.
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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4.
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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5.
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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6.
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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7.
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.
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Hydration Interventions for older people living in residential and nursing care homes: overview of the literature.
Cook, G, Hodgson, P, Thompson, J, Bainbridge, L, Johnson, A, Storey, P
British medical bulletin. 2019;(1):71-79
Abstract
INTRODUCTION Care home populations experiencing high levels of multi-morbidity and dementia require support from caregivers to meet their hydration requirements. This article provides an overview of literature related to hydration interventions and highlights gaps in knowledge. SOURCES OF DATA This paper draws on UK-focused literature from Applied Social Sciences Index and Abstracts (ASSIA), CINAHL, Medline, Proquest Hospital Premium Collection, Cochrane Library and RCN databases on hydration interventions for older people living with multi-morbidity and dementia in care homes. AREAS OF AGREEMENT Fluid intake is too low in care home residents, and no single hydration intervention is effective in addressing the complex problems that older residents present. AREAS OF CONTROVERSY There is a lack of consensus about how much fluid an older person should consume daily for optimum health. There is also lack of agreement about what interventions are effective in supporting individuals with complex physical and cognitive problems to achieve daily fluid intake targets. GROWING POINTS To improve hydration care for residents, care home teams should be competent in the delivery of hydration care, and work closely with integrated multi-professional healthcare specialists to provide proactive case management. AREAS TIMELY FOR DEVELOPING RESEARCH There is a need for understanding of what hydration practices and processes are effective for care home residents and including these in multi-component interventions.
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Fluid Needs for Training, Competition, and Recovery in Track-and-Field Athletes.
Casa, DJ, Cheuvront, SN, Galloway, SD, Shirreffs, SM
International journal of sport nutrition and exercise metabolism. 2019;(2):175-180
Abstract
The 2019 International Amateur Athletics Federation Track-and-Field World Championships will take place in Qatar in the Middle East. The 2020 Summer Olympics will take place in Tokyo, Japan. It is quite likely that these events may set the record for hottest competitions in the recorded history of both the Track-and-Field World Championships and Olympic Games. Given the extreme heat in which track-and-field athletes will need to train and compete for these games, the importance of hydration is amplified more than in previous years. The diverse nature of track-and-field events, training programs, and individuality of athletes taking part inevitably means that fluid needs will be highly variable. Track-and-field events can be classified as low, moderate, or high risk for dehydration based on typical training and competition scenarios, fluid availability, and anticipated sweat losses. This paper reviews the risks of dehydration and potential consequences to performance in track-and-field events. The authors also discuss strategies for mitigating the risk of dehydration.
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10.
[How to improve hydration and fluid intake in institutionalized older people? A scientific literature review].
Masot, O, Iglesias Millán, A, Nuin, C, Miranda, J, Lavedán, A, Botigué, T
Nutricion hospitalaria. 2018;(6):1441-1449
Abstract
BACKGROUND residents are vulnerable to suffer of dehydration due to physiological changes and the physical and cognitive limitations. AIM: to handle this situation, it has been decided to evaluate the interventions which are carried out for the management of dehydration and low fluid intake in older people living in nursing homes. METHODS the revised scientific literature review methodology of PRISMA was applied. An electronic database search was performed in PubMed, Scopus, CINAHL and other sources databases. The literature search was carried out between October 2016 and January 2017. Out of a total of 3,379 articles extracted, eleven studies were selected for analysis. In addition, their quality was assessed through Cochrane and the Newcastle-Ottawa Scale. RESULTS the risk of bias in the studies was mostly medium. Regarding the results, the interventions were classified according to whether they were invasive or non-invasive. Invasive interventions were intravenous and/or subcutaneous fluid therapy. Their effectiveness was related to the clinical improvement of dehydration. However, local reactions appeared. Non-invasive interventions focused on the individualized assistance, the stimulation to drink more and the consideration of the preferences of each resident, producing an increase in fluid intake and an improvement in analytical parameters. CONCLUSIONS given the peculiarities of the institutionalized elderly population, both types of intervention have been shown to have a positive effect on improving hydration. Nonetheless, non-invasive interventions have confirmed to be more efficient given their simplicity of application and cause fewer adverse effects.