La sed ¿un mecanismo suficiente para lograr euhidratación?: una revisión narrativa / Is thirst sufficient as a mechanism for achieving euhydration? a narrative review

Capitán, C. y Aragón, L.F. (2023). La sed ¿un mecanismo suficiente para lograr euhidratación?: una revisión narrativa. PENSAR EN MOVIMIENTO: Revista de Ciencias del Ejercicio y la Salud, 21(1), 1-16. El papel de la percepción de sed para mantener el balance hídrico ha sido ampliamente estudiado, tanto durante el ejercicio como después de este. Sin embargo, la forma de evaluarla y la eficacia de los instrumentos existentes son aún áreas que necesitan más investigación. El objetivo de esta revisión fue integrar, de forma general, la información disponible en la literatura sobre el funcionamiento del mecanismo de la sed como respuesta a la deshidratación durante y después del ejercicio. Se explican los mecanismos fisiológicos y las respuestas de estos durante y posterior al ejercicio; además, se describen los instrumentos disponibles en la literatura científica, sus debilidades y fortalezas, y se plantea una serie de preguntas que aún no tienen respuesta en el área. En esta revisión se presenta el aspecto teórico de los mecanismos de la sed, además, se discuten los estudios científicos que respaldan o refutan el comportamiento de estos mecanismos en el ejercicio. Finalmente, se hace un resumen de las principales conclusiones extraídas de la literatura científica sobre la sed como un mecanismo suficiente para prevenir la deshidratación tanto durante como después del ejercicio.

Capitán, C. y Aragón, L.F. (2023). Is thirst sufficient as a mechanism for achieving euhydration? a narrative review. PENSAR EN MOVIMIENTO: Revista de Ciencias del Ejercicio y la Salud, 21(1), 1-16. The role of thirst perception for keeping hydric balance, both during and after exercise, has been extensively studied. However, the way to assess it and the effectiveness of the existing instruments are areas that still require further research. The objective of this review is to integrate, in a general way, the information available in the literature on the functioning of the thirst mechanism as a response to dehydration during and after exercise. The physiological mechanisms and their responses during and after exercise are explained. In addition, a description of the instruments available in scientific literature is included, together with their weaknesses and strengths, and a series of as yet unanswered questions in this area are raised. This review presents the theoretical aspect of thirst mechanisms, and discusses the scientific studies that support or refute the behavior of these mechanisms in exercise. Finally, a summary is made of the major conclusions drawn from the scientific literature on thirst as a sufficient mechanism to prevent dehydration both during and after exercise.

Capitán, C. y Aragón, L.F. (2023). A sede é um mecanismo suficiente para alcançar a hidratação? uma revisão narrativa. PENSAR EN MOVIMIENTO: Revista de Ciencias del Ejercicio y la Salud, 21(1), 1-16. O papel da percepção da sede na manutenção do equilíbrio hídrico tem sido amplamente estudado, tanto durante quanto após o exercício. Entretanto, como avaliá-la e a eficácia dos instrumentos existentes ainda são áreas que necessitam de mais pesquisas. Esta revisão visou integrar, de forma geral, as informações disponíveis na literatura sobre o funcionamento do mecanismo da sede em resposta à desidratação durante e após o exercício. Ele explica os mecanismos fisiológicos e suas respostas durante e após o exercício, descreve os instrumentos disponíveis na literatura científica, seus pontos fracos e fortes, e levanta uma série de questões que permanecem sem resposta no campo. Esta revisão apresenta o aspecto teórico dos mecanismos da sede e discute os estudos científicos que respaldam ou refutam o comportamento desses mecanismos no exercício. Finalmente, é feito um resumo das principais conclusões extraídas da literatura científica sobre a sede como mecanismo suficiente para prevenir a desidratação tanto durante quanto após o exercício.

Post-Exercise Voluntary Drinking Cessation Is Associated with the Normalization of Plasma Osmolality and Thirst Perception, but Not of Urine Indicators or Net Fluid Balance.

Post-exercise rehydration has been widely studied, with particular emphasis on retention of ingested fluid; comparatively little research has been conducted on why we drink more or less. To identify physiological values corresponding to voluntary drinking cessation (VDC), nine males exercised intermittently at 70−80% HRmax in the heat (WBGT = 28.1 ± 0.7 °C) to achieve a dehydration of approximately 4.0% body mass (BM). After exercise, participants were instructed to drink water as long and as much as they needed. Urine color (Ucolor), specific gravity (USG), osmolality (Uosm), plasma osmolality (Posm), fullness, BM, and thirst perception (TP) were measured pre- and post-exercise and at VDC. Each variable was compared for the three points in time with a one-way ANOVA. Participants reached dehydration of −3.6 ± 0.3% BM. Pre-exercise USG (1.022 ± 0.004) was lower than at VDC (1.029 ± 0.004, p = 0.022), Uosm did not change over time (p = 0.217), and Ucolor was lower pre-exercise (3.4 ± 0.7) vs. post-exercise (5.5 ± 1.23, p = 0.0008) and vs. VDC (6.3 ± 1.1, p < 0.0001). Posm showed a difference between pre-exercise (289.5 ± 2.3) and post-exercise (297.8 ± 3.9, p = 0.0006) and between post-exercise and VDC (287.3 ± 5.4, p < 0.0001). TP post-exercise (96.4 ± 4.34) was significantly higher than pre-exercise (36.2 ± 19.1) and VDC (25.0 ± 18.2, p < 0.0001). At VDC, participants had recovered 58.7 ± 12.1% of BM loss. At the point of voluntary drinking cessation, Posm and thirst perception had returned to their pre-exercise values, while rehydration relative to initial BM was still incomplete.

Awareness of Fluid Losses Does Not Impact Thirst during Exercise in the Heat: A Double-Blind, Cross-Over Study.

BACKGROUND: Thirst has been used as an indicator of dehydration; however, as a perception, we hypothesized that it could be affected by received information related to fluid losses. The purpose of this study was to identify whether awareness of water loss can impact thirst perception during exercise in the heat. METHODS: Eleven males participated in two sessions in random order, receiving true or false information about their fluid losses every 30 min. Thirst perception (TP), actual dehydration, stomach fullness, and heat perception were measured every 30 min during intermittent exercise until dehydrated by ~4% body mass (BM). Post exercise, they ingested water ad libitum for 30 min. RESULTS: Pre-exercise BM, TP, and hydration status were not different between sessions (p > 0.05). As dehydration progressed during exercise, TP increased significantly (p = 0.001), but it was the same for both sessions (p = 0.447). Post-exercise water ingestion was almost identical (p = 0.949) in the two sessions. CONCLUSION: In this study, thirst was a good indicator of fluid needs during exercise in the heat when no fluid was ingested, regardless of receiving true or false water loss information.

Validity and Reliability of a Water Frequency Questionnaire to Estimate Daily Total Water Intake in Adults.

The purpose of this investigation was to assess the validity and reliability of a seven-day water frequency questionnaire (TWI-FQ) to estimate daily total water intake (TWI) in comparison to a water turnover objective reference value via deuterium oxide (D2O). Data collection occurred over 3 weeks, with a wash-out period during week two. Healthy adults (n = 98; 52% female; 41 ± 14 y; BMI, 26.4 ± 5.5 kg·m-2) retrospectively self-reported consumption frequencies of 17 liquids and 35 foods with specified volumes/amounts for weeks one and three via TWI-FQ. Standard water content values were utilized to determine the volume of water consumed from each liquid and food for calculation of mean daily TWI for each week. Diet records were completed daily during week two to estimate metabolic water production. To assess validity of the TWI-FQ, participants consumed D2O at the start of each week and provided urine samples immediately before ingestion, the following day, and at the end of the week to calculate water turnover. Metabolic water was subtracted from water turnover to estimate TWI. TWI-FQ validity was assessed via Bland-Altman plot for multiple observations. Reliability was assessed via intraclass correlation and Pearson's correlation between weeks. TWI-FQ significantly underestimated D2O TWI by -350 ± 1,431 mL·d-1 (95% confidence interval (CI): -551, -149 mL·d-1). TWI-FQ TWI was significantly correlated (r = 0.707, P <0.01) and not different (198 ± 1,180 mL·d-1, 95% CI: -38, 435 mL·d-1) between weeks. TWI-FQ intraclass correlation = 0.706 was significant [95% CI: 0.591, 0.793; F (97, 98) = 5.799], indicating moderate test-retest reliability. While this tool would not be suitable for individual TWI assessment, the magnitude of bias may be acceptable for assessment at the sample-level.

Combining urine color and void number to assess hydration in adults and children.

BACKGROUND/OBJECTIVES: To test the diagnostic ability of two combined practical markers for elevated urine osmolality (underhydration) in free-living adults and children. SUBJECTS/METHODS: One hundred and one healthy adults (females n = 52, 40 ± 14 y, 1.70 ± 0.95 m, 76.7 ± 17.4 kg, 26.5 ± 5.5 kg/m2) and 210 children (females = 105, 1.49 ± 0.13 m, 43.4 ± 12.6 kg, 19.2 ± 3.2 kg m-2) collected urine for 24-h. Urine was analyzed for urine osmolality (UOsm), color (UC), while the number of voids (void) was also recorded. Receiver Operating Characteristic (ROC) analysis was performed for UC, void, and combination of UC and void, to determine markers' diagnostic ability for detecting underhydration based on elevated UOsm (UOsm ≥ 800 mmol kg-1). RESULTS: Linear regression analysis revealed that UC was significantly associated with UOsm in both adults (R2 = 0.38; P < 0.001) and children (R2 = 0.45; P < 0.001). Void was significantly associated with UOsm in both adults (R2 = 0.13; P < 0.001) and children (R2 = 0.15; P < 0.001). In adults, when UC > 3 and void <7 were combined, the overall diagnostic ability for underhydration was 97% with sensitivity and specificity of 100% and 88%, respectively. In children, UC > 3 and void <5 had an overall diagnostic ability for underhydration of 89% with sensitivity and specificity of 100% and 62%, respectively. CONCLUSIONS: Urine color alone and the combination of urine color with void number can a valid and simple field-measure to detect underhydration based on elevated urine osmolality.

Smartphone-Based Analysis of Urine Reagent Strips Is Inaccurate for Assessing Underhydration.

Background: Proper hydration is vital for both exercise and general health. Although various methods for hydration assessment exist, many are not valid for either use or never tested. Introduction: The purpose of this study was to determine whether the uChek© smart phone application can be used to diagnose underhydration based on elevated urine specific gravity (USG) assessed by refractometry. Methods: One hundred forty-seven (n = 147) fresh human urine samples from young and middle-age adults were analyzed for USG with a refractometer and the uChek© application by reading the Siemens Multistix 10G urine reagent strip. Results: Bland-Altman analysis showed agreement of the two methods of assessment. Overall diagnostic ability of the uChek© to identify underhydration was fair (area under the curve 79%). However, the sensitivity to correctly identify underhydration was poor (60%) as well as the specificity of correctly identifying euhydration (53%). Conclusion: The uChek© application does not accurately detect underhydration.

Urine Reagent Strips Are Inaccurate for Assessing Hypohydration: A Brief Report.

OBJECTIVE: To assess the diagnostic ability of urine reagent strips to identify hypohydration based on urine specific gravity (USG). DESIGN: This study examined the agreement of USG between strips and refractometry with Bland-Altman, whereas the diagnostic ability of the strips to assess hypohydration was performed by receiver operating characteristic analysis. SETTING: Arkansas high school football preseason practice. PARTICIPANTS: Four hundred fourteen fresh urine samples were analyzed. MAIN OUTCOME MEASURES: Urine specific gravity was assessed by both reagent strips and refractometry. Cutoffs of >1.020 and >1.025 were used for identifying hypohydration. RESULTS: Bland-Altman analysis showed agreement of the 2 methods. Overall diagnostic ability of the urine strip to identify hypohydration was fair (area under the curve 72%-78%). However, the sensitivity to correctly identify hypohydration was poor (63%-71%), and the specificity of correctly identifying euhydration was poor to fair (68%-83%). CONCLUSION: The urine strip method is not valid for assessing hypohydration.

Percepción de la sed durante el ejercicio y en la rehidratación ad libitum postejercicio en calor húmedo y seco / Thirst perception during exercise and post exercise ad libitum rehydration in dry and humid heat / Percepção da sede durante o exercício e na reidratação ad libitum pós-exercício no calor úmido e seco

Resumen Capitán-Jiménez, C. y Aragón-Vargas, L.F. (2018). Percepción de la sed durante el ejercicio y en la rehidratación ad libitum postejercicio en calor húmedo y seco. PENSAR EN MOVIMIENTO: Revista de Ciencias del Ejercicio y la Salud, 16(2), 1-18. Este estudio experimental fue diseñado para evaluar durante el ejercicio y la rehidratación ad libitum postejercicio si las percepciones subjetivas de sed y calor, así como la ingesta voluntaria de agua, son distintas en dos condiciones ambientales diferentes, pero equivalentes en cuanto al índice de estrés térmico. Métodos: 14 participantes se ejercitaron en dos ocasiones en un cuarto de clima controlado (WBGT≈28.5°C): una vez para el calor seco (SECO, TBS=33.8°C, HR=53%) y una para el calor húmedo (HUM, TBS=32.1°C y HR=67 %), sin ingesta de fluidos, hasta alcanzar una deshidratación equivalente al 4 % MC. Las percepciones de sed, calor, llenura y cólico se midieron cada 30 min durante el ejercicio. Posteriormente, ingirieron agua ad libitum durante 90 minutos. También se midió la ingesta voluntaria de agua. Resultados: Durante el ejercicio, la percepción de sed fue la misma para ambas condiciones (SECO 64.4423.38, HUM 67.3220.41mm; p=0.409), pero aumentó con el tiempo (p=0.0001). Lo mismo ocurrió con la percepción de calor: no hubo diferencia entre las condiciones (SECO 6.340.50, HUM 6.400.37ua; p=0.423), pero aumentó a través del tiempo (p=0.001). Al final de la rehidratación, la percepción de calor fue mayor para el calor seco (5.3 ± 0.2ua) que para el calor húmedo (4.7 ± 0.2ua, p=0.006). La sed al final del ejercicio (85.8 ± 19.4mm) no mostró correlación significativa con la deshidratación real (3.82 ± 0.18% MC, r=-0.14, p=0.48) ni con el consumo voluntario de agua (1843 ± 587 ml, r=-0.04, p=0.85). No hubo correlación entre la pérdida de sudor real (2766 ± 700 ml) y la ingesta voluntaria de agua (r=0.16, p=0.42). La asociación entre el balance neto de fluidos y la percepción de la sed fue de R2a= 0.70 (p=0.001). Conclusiones: la percepción de sed y calor fue la misma cuando se realizó ejercicio en dos condiciones ambientales diferentes con el mismo nivel de estrés térmico. La escala de percepción de la sed fue capaz de detectar la deshidratación progresiva consistentemente: cuanto mayor fue la deshidratación en el tiempo, mayor fue la sed. Sin embargo, los resultados de este estudio no apoyan la teoría de que la ingesta voluntaria de agua es adecuada para reponer las pérdidas de sudor después del ejercicio.

Abstract Capitán-Jiménez, C. & Aragón-Vargas, L.F. (2018). Thirst perception during exercise and post exercise ad libitum rehydration in dry and humid heat. PENSAR EN MOVIMIENTO: Revista de Ciencias del Ejercicio y la Salud, 16(2), 1-18. This experimental study was designed to evaluate whether subjective perceptions of thirst and heat and voluntary water intake are different in two distinct environmental conditions but equivalent in terms of the thermal stress index, during exercise and post-exercise ad libitum rehydration. Methods: 14 participants exercised twice in a climate controlled room (WBGT≈28.5°C): once for dry heat (DRY, DBT=33.8°C, RH=53%) and once for humid heat (HUM, DBT=32.1°C and RH=67%), without fluid intake, until reaching dehydration equivalent to 4% BM. Perceptions of thirst, heat, fullness and colic were measured every 30 min during exercise. Subsequently, participants ingested water ad libitum for 90 minutes. Voluntary intake of water was also measured. Results: During exercise, thirst perception was the same for both conditions (DRY 64.44±23.38, HUM 67.32±20.41mm, p=0.409); however, it increased over time (p=0.0001). The same situation happened with heat perception: there was no difference between conditions (DRY 6.34±0.50, HUM 6.40±0.37ua, p=0.423), but it also increased over time (p=0.001). At the end of rehydration, heat perception was greater for dry heat (5.3 ± 0.2ua) than for moist heat (4.7 ± 0.2ua, p=0.006). At the end of the exercise, thirst (85.8 ± 19.4mm) showed no significant correlation with actual dehydration (3.82 ± 0.18% BM, r=-0.14, p=0.48) or with voluntary water intake (1843 ± 587 ml, r=-0.04, p=0.85). There was no correlation between the actual sweat loss (2766 ± 700 ml) and the voluntary water intake (r=0.16, p=0.42). Ratio between net fluid balance and thirst perception was R2a=0.70 (p=0.001). Conclusions: thirst and heat perceptions were the same when exercising in two different environmental conditions with the same level of heat stress. The thirst perception scale was able to detect progressive dehydration in a consistent manner: the greater the dehydration over time, the greater the thirst. However, the results of this study do not support the theory that voluntary water intake is adequate to replenish sweat loss after exercise.

Resumo Capitán-Jiménez, C. & Aragón-Vargas, L.F. (2018). Percepção da sede durante o exercício e na reidratação ad libitum pós-exercício no calor úmido e seco. PENSAR EN MOVIMIENTO: Revista de Ciencias del Ejercicio y la Salud, 16(2), 1-18. Este estudo experimental foi desenhado para avaliar, durante o exercício e a reidratação ad libitum pós-exercício, se as percepções subjetivas de sede e calor, como também a ingestão voluntária de água, são distintas em duas condições ambientais diferentes, porém equivalentes com relação ao índice de estresse térmico. Métodos: 14 participantes se exercitaram em duas ocasiões em um quarto de clima controlado (WBGT≈28.5°C): uma vez para o calor seco (SECO, TBS=33.8°C, HR=53%) e uma para o calor úmido (HUM, TBS=32.1°C e HR=67 %), sem ingerir fluidos, até alcançar uma desidratação equivalente a 4 % MC. As percepções de sede, calor, fartura e cólica foram medidas a cada 30 min durante o exercício. Posteriormente, ingeriram água ad libitum durante 90 minutos. Também foi medida a ingestão voluntária de água. Resultados: Durante o exercício, a percepção de sede foi a mesma para ambas as condições (SECO 64.4423.38, HUM 67.3220.41mm; p=0.409), porém aumentou com o tempo (p=0.0001). O mesmo ocorreu com a percepção de calor: não houve diferença entre as condições (SECO 6.340.50, HUM 6.400.37ua; p=0.423), mas aumentou através do tempo (p=0.001). No final da reidratação, a percepção de calor foi maior para o calor seco (5.3 ± 0.2ua) do que para o calor úmido (4.7 ± 0.2ua, p=0.006). A sede, no final do exercício (85.8 ± 19.4mm) não mostrou correlação significativa com a desidratação real (3.82 ± 0.18% MC, r=-0.14, p=0.48) e nem com o consumo voluntário de água (1843 ± 587 ml, r=-0.04, p=0.85). Não houve correlação entre a perda de suor real (2766 ± 700 ml) e a ingestão voluntária de água (r=0.16, p=0.42). A associação entre o equilíbrio neto de fluidos e a percepção da sede foi de R2a= 0.70 (p=0.001). Conclusões: a percepção de sede e calor foi a mesma quando se realizou exercício em duas condições ambientais diferentes com o mesmo nível de estresse térmico. A escala de percepção da sede foi capaz de detectar a desidratação progressiva consistentemente: quanto maior foi a desidratação no tempo, maior foi a sede. Porém, os resultados deste estudo não apoiam a teoria de que a ingestão voluntária de água é adequada para repor as perdas de suor depois do exercício.

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.

The Effect of Storing Temperature and Duration on Urinary Hydration Markers.

The purpose of this investigation was to quantify the effects of storage temperature, duration, and the urinary sediment on urinary hydration markers. Thirty-six human urine samples were analyzed fresh and then the remaining sample was separated into 24 separate vials, six in each of the following four temperatures: 22 °C, 7 °C, -20 °C, and -80 °C. Two of each sample stored in any given temperature, were analyzed after 1, 2, and 7 days either following vortexing or centrifugation. Each urine sample was analyzed for osmolality (UOsm), urine specific gravity (USG), and urine color (UC). UOsm was stable at 22 °C, for 1 day (+5-9 mmol∙kg-1, p > .05) and at 7 °C, UOsm up to 7 days (+8-8 mmol∙kg-1, p > .05). At -20 and -80 °C, UOsm decreased after 1, 2, and 7 days (9-61 mmol∙kg-1, p < .05). Vortexing the sample before analysis further decreased only UOsm in the -20 °C and -80 °C storage. USG remained stable up to 7 days when samples were stored in 22 °C or 7 °C (p > .05) but declined significantly when stored in -20 °C, and -80 °C (p < .001). UC was not stable in any of the storing conditions for 1, 2, and 7 days. In conclusion, these data indicate that urine specimens analyzed for UOsm or USG remained stable in refrigerated (7 °C) environment for up to 7 days, and in room temperature for 1 day. However, freezing (-20 and -80 °C) samples significantly decreased the values of hydration markers.