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Background/Objectives: Ultra-endurance running (UER) presents unique hydration challenges due to prolonged duration, variable terrain, environmental extremes, and gastrointestinal limitations. Athletes often use either programmed fluid intake (PFI), which prescribes fluid volumes based on estimated sweat rate, or thirst-driven fluid intake (TDFI), which relies on internal cues. This review examines the effectiveness and limitations of each strategy in the context of UER performance and safety. Methods: A narrative review was conducted using a targeted selection of peer-reviewed studies. Both laboratory- and field-based research were included to evaluate the physiological rationale, practical feasibility, and outcomes associated with PFI and TDFI. A total of six studies (five field-based ultra-endurance and one laboratory-based endurance protocols) were included for narrative synthesis. Results: Laboratory trials support PFI for preserving plasma volume, reducing cardiovascular strain, and improving performance in prolonged exercise under controlled conditions. However, real-world ultra-endurance events often involve environmental and logistical challenges that limit the applicability of rigid hydration strategies. Field studies demonstrate that TDFI is safe and effective for many experienced athletes, with no increased incidence of exercise-associated hyponatremia or measurable performance impairment, even with moderate body mass loss. Still, TDFI may underperform in individuals with high sweat rates or impaired thirst perception. Conclusions: Neither strategy seems universally superior. A hybrid model that integrates individual sweat testing, environmental context, and responsiveness to internal cues may offer the most practical and effective hydration approach in ultra-endurance running. Continued research is needed to validate hydration strategies under field conditions and to inform personalized, performance-oriented guidelines.

Background: Investigating fluid consumption among children and adolescents poses a challenge due to varying dietary behaviors and hydration needs. This systematic review aims to assess total water intake (TWI) and total fluid intake (TFI) in children and adolescents, focusing on gender differences and adherence to reference values proposed by the European Food Safety Authority (EFSA) and the Institute of Medicine (IOM). Methods: A systematic literature search of PubMed, Scopus, and Scholar was conducted to identify studies published between 2004 and 2024 reporting on TWI and TFI for children and adolescents. Studies were included if they reported fluid intake data in healthy populations, provided quantitative measures of TWI or TFI, and aligned with the EFSA or IOM reference values. From 8731 initial articles, 24 studies met the inclusion criteria. Data were synthesized narratively, and compliance with hydration guidelines was assessed. Results: The review included 24 studies, encompassing 16,254 children and 15,367 adolescents. The majority of participants failed to meet the recommended guidelines. Only one study reported compliance with the recommended TWI values, while four studies in children and four in adolescents showed adherence to the recommended TFI values. Conclusions: The results underscore a widespread inadequacy in achieving the hydration guidelines among children and adolescents, emphasizing the need for targeted interventions to improve fluid intake. Public health interventions are needed to promote adequate fluid intake, particularly in populations at risk of dehydration-related health outcomes. Future research should focus on identifying barriers to adequate hydration and developing targeted strategies to improve fluid intake behaviors.

Background Normal distribution of body fluid is important for maintaining health through the balance of water metabolism. Studies have shown that disease states and diuretics perturb the balance and then induce abnormal intracellular/extracellular fluid ratio. However, there are relatively few researches on the associations between water intakes and body fluid. The objective of this study was to explore the association between body fluid and water intake. Methods A total of 159 young adults in Baoding, China were recruited in this cross-sectional survey and completeness of follow-up was 98.1%. A 7-day fluid specific diary was used to record total fluid intake (TFI). Water intake from foods (FWI) for 3 days was measured using the methods of weighting, duplicate portion method and laboratory analysis by researchers. Body fluid was measured using bioelectrical impedance analysis. Results Total body water (TBW), intracellular fluid (ICF) and extracellular fluid (ECF) of participants were 32.8[28.0,39.2], 20.5[17.3,24.5] and 12.4[10.7,14.7], (kg). This represented 55.2 ± 6.2, 34.4 ± 4.0 and 20.8 ± 2.3 (%) of body weight (BW), respectively. ICF, ECF and TBW among male participants who drank more than or equal to adequate TFI was higher than those who drank less ( Z  = -1.985, p  = 0.047; Z  = -2.134, p  = 0.033; Z  = -2.053, p  = 0.040). Among both males and females, the values of TBW/BW in participants whose TWI met or exceeded the AI were higher than those with TWI less than AI ( t  = − 2.011, p  = 0.046; t  = − 2.716, p  = 0.008). Among all participants, there was moderate correlation between water intakes (TFI/BW, FWI/BW and TWI/BW) and body fluid (ICF/BW,ECF/BW and TBW/BW) ( p  < 0.01 for all). Same correlations were found among both males and females. Conclusion There is a certain degree of association between water intake and body fluid. However, whether TFI or TWI achieve AI or not do not disturb the balance on the distribution of body fluid. More studies should be conducted to find the diagnostic threshold on TFI and TWI which may disrupt the distribution of body fluid so as to prevent related diseases. Trial registration Chinese clinical trial registry. Name of the registry: Relationship of drinking water and urination. Trial registration number: ChiCTR-ROC-17010320. Date of registration: 01/04/2017. URL of trial registry record: http://www.chictr.org.cn/edit.aspx?pid=17601&htm=4 .

This study tested the accuracy of a novel, limited-availability web application (H2QTM) for predicting sweat rates in a variety of sports using estimates of energy expenditure and air temperature only. The application of predictions for group water planning was investigated for soccer match play. Fourteen open literature studies were identified where group sweat rates were reported (n = 20 group means comprising 230 individual observations from 179 athletes) with fidelity. Sports represented included: walking, cycling, swimming, and soccer match play. The accuracy of H2QTM sweat rates was tested by comparing to measured group sweat rates using the concordance correlation coefficient (CCC) with 95% confidence interval [CI]. The relative absolute error (RAE) with 95% [CI] was also assessed, whereby the mean absolute error was expressed relative to an acceptance limit of 0.250 L/h. The CCC was 0.98 [0.95, 0.99] and the RAE was 0.449 [0.279, 0.620], indicating that the prediction error was on average 0.112 L/h. The RAE was < 1.0 for 19/20 observations (95%). Drink volumes modeled as a proxy for sweat losses during soccer match play prevented dehydration (< 1% loss of body mass). The H2QTM web application demonstrated high group sweat prediction accuracy for the variety of sports activities tested. Water planning for soccer match play suggests the feasibility of easily and accurately predicting sweat rates to plan group water needs and promote optimal hydration in training and/or competition.

Monitoring fluid intake is essential to help people manage their individual fluid intake behaviors and achieve adequate hydration. Previous studies of fluid intake assessment approaches based on inertial sensors can be categorized into wrist-worn-based and smart-container-based approaches. This study aims to analyze wrist-worn-based and smart-container-based fluid intake assessment approaches using inertial sensors. The comparison of these two approaches should be analyzed according to gesture recognition and volume estimation. In addition, the influence of the fill level and sip size information on the performance is explored in this study. The accuracy of gesture recognition with postprocessing is 92.89% and 91.8% for the wrist-worn-based approach and smart-container-based approach, respectively. For volume estimation, sip-size-dependent models can achieve better performance than general SVR models for both wrist-worn-based and smart-container-based approaches. The improvement of MAPE, MAD, and RMSE can reach over 50% except MAPE for small sip sizes. The results demonstrate that the sip size information and recognition performance are important for fluid intake assessment approaches.

A hot working environment can cause health problems for workers, one of them being dehydration. The hydration status of a worker can be influenced by the characteristic of the worker, physical environmental factors, and fluid intake. The objective of this study is to determine the relationship between workers’ characteristics, physical environmental factors, and fluid intake with the hydration status of workers. This study was conducted using the cross-sectional design method and used a simple random sampling technique to select  17 respondents and 17 home industries originally derived from 20 respondents and 20 home industries. The research location was on Jalan Banyu Urip Lor X Surabaya. Data were analyzed using cross-tabulation and fisher’s exact test with a confidence level of 95%. The data were collected through interviews, measurements, questionnaires, and verification. The results showed that there was a significant relationship between physical environmental factors, which included temperature (p = 0.002), humidity (p = 0.029), and fluid intake (p = 0.029), with the hydration status of workers. In general, it can be concluded that physical environmental factors and fluid intake are relevant towards the hydration status of workers. Therefore, it is recommended that the workers improve air circulation in the room by adding natural ventilation, an exhaust fan in the kitchen, and are advised to consume enough mineral water while working.Keywords: temperature, humidity, fluid intake, hydration status

Introduction Previous research established significant relationships between total fluid intake (TFI) and urinary biomarkers of the hydration process in free-living males and females; however, the nature of this relationship is not known for pregnant (PREG) and lactating (LACT) women. Purpose To determine the relationship between urinary and hematological hydration biomarkers with TFI in PREG and LACT. Methods Eighteen PREG/LACT (age: 31 ± 3 years, pre-pregnancy BMI: 24.26 ± 5.85 kg m −2 ) collected 24-h urine samples, recorded TFI, and provided a blood sample at 5 time points (15 ± 2, 26 ± 1, 37 ± 1 weeks gestation, 3 ± 1 and 9 ± 1 weeks postpartum during lactation); 18 pair-matched non-pregnant (NP), non-lactating (NL) women (age: 29 ± 4 years, BMI: 24.1 ± 3.7 kg m −2 ) provided samples at similar time intervals. Twenty-four-hour urine volume ( U VOL ), osmolality ( U OSM ), specific gravity ( U SG ), and color ( U COL ) were measured. Hematocrit, serum osmolality ( S OSM ), and serum total protein ( S TP ) were measured in blood. Results Significant relationships were present between TFI and urinary biomarkers in all women ( P  < 0.004); these relationships were not different between PREG and NP, and LACT and NL, except U VOL in PREG ( P  = 0.0017). No significant relationships between TFI and hematological biomarkers existed ( P  > 0.05). Conclusion Urinary biomarkers of hydration, but not hematological biomarkers, have a strong relationship with TFI in PREG, LACT, NP, and NL women. These data suggest that urinary biomarkers of hydration reflect TFI during pregnancy and breast-feeding.

Water is a critical nutrient that is important for the maintenance of the physiological function of the human body. This article aimed to investigate the effects of the amount and frequency of fluid intake on cognitive performance and mood. A double-blinded randomized controlled trial was designed and implemented on college students aged 18–23 years in Baoding, China. Participants were randomly assigned into one of three groups: the recommended behavior group (RB group) who drank 200 mL of water every 2 h, the half amount group (HA group) who drank 100 mL of water every 2 h, and the high frequency group (HF group) who drank 110 mL of water every 1 h. The intervention lasted 2 days. Urine osmolality, cognitive performance, and mood of participants in each group were compared using the one-way analysis of variance (ANOVA). A total of 92 participants (46 females, 46 males) completed this study with a completion rate of 95.8%. The urine osmolality of the HA group was higher than that of the RB group and the HF group at two time points (p < 0.05). At time point 1, the scores in the portrait memory test and vigor were statistically different (F = 20.45, p < 0.001; F = 5.46, p = 0.006). It was found that the scores for the portrait memory test in the RB group were lower than those in the HA group and the HF group (p = 0.007; p < 0.001), while the scores of the HF group were higher than those of the HA group (p < 0.001). The scores for vigor in the RB group were significantly higher than those of the HA group (p = 0.006), and they were also significantly higher than those of the HF group (p = 0.004). At time point 2, only the scores for vigor were statistically different (F = 3.80, p = 0.026). It was found that the scores for vigor in the RB group were higher than those in the HA group and HF group (p = 0.018; p = 0.019). Both the amount and frequency of fluid intake may affect urine osmolality and vigor, but these factors have limited impacts on cognitive performance. Rational fluid intake behavior may be beneficial to improve the hydration status and mood of young adults. More research is needed, especially experimental research, to allow causal conclusions to be drawn.

Introduction: Water is a critical nutrient, and it is important for the maintenance of the physiological function of the human body [1 -3 ]. In addition to fluid amounts, fluid intake frequency is also important for hydration status [4 , 5 ]. At present, only few guidelines mention fluid intake behavior that recommend drinking water frequently while in small quantities, however, there is no scientific evidence to support it. Therefore, it is necessary to explore the appropriate fluid intake behavior. Objective: The objective of this study is to evaluate the influence of different fluid intake behavior on cognition and mood, to provide scientific basis for proposing the appropriate fluid intake behavior. Methods: A double-blinded randomized controlled trial was designed and implemented among college students aged 18–23 years in Baoding, China. Subjects were randomly assigned into each of 3 groups using a random number generated by computer software: the subjects consuming plain water 200 mL/2 h, that is, 1,600 mL during whole day (group 1), 100 mL/2 h, that is, 800 mL during whole day (group 2), and 110 mL/1 h, that is, 1,650 mL during whole day (group 3), respectively. Subjects were asked to fast from 11:00 p.m., without consuming any foods or drinks the day before the intervention. From 8:00 a.m. to 10:00 p.m. of the first study day, subjects consumed water according to the instructions and repeated it from 8:00 a.m. to 4:00 p.m. of the second study day. Cognition, mood, and urine osmolality were collected twice at 10:00 a.m. (time 1) and 4:00 p.m. (time 2) of the second study day (shown in Fig. 1 ). Results: A total of 92 subjects (46 males, 46 females) completed this study. It was found that the increasing fluid intake amounts lead to an increase in urine output and a decrease in urine osmolality (p < 0.05). Use the mixed models to compare measurements for groups 1 and 2, which showed that when compared with those drinking 800 mL per day, people who drank 1,600 mL per day scored higher in vigor (11.8 vs. 9.1, p < 0.05) and portrait memory test (22.6 vs. 20.8, p < 0.05) but lower in total mood disturbance (90.8 vs. 97.8, p < 0.05). By comparing groups 1 and 3, the results indicated that compared with drinking 8 times per day, people who drank 15 times per day scored lower in portrait memory test (21.8 vs. 22.6, p < 0.05) and hunger (3.3 vs. 3.6, p < 0.05). Conclusions: Reasonable fluid intake behavior may be beneficial to improve the cognition and mood of college students. The fluid intake behavior, which is consuming water 200 mL each time and 8 times per day, is recommended. More studies are needed to advise people to have health-beneficial fluid intake behavior.

Patients undergoing major abdominal surgery received restrictive or liberal intravenous fluids during surgery and up to 24 hours thereafter. The restrictive regimen did not improve disability-free survival and resulted in increased acute kidney injury.