OBJECTIVE: Athletes are commonly exposed to exercise-induced dehydration. However, the best method to detect dehydration under this circumstance is not clear. This study aimed to analyze pre- and post-dehydration measurements of biomarkers, including saliva osmolality (SOsm), urine osmolality (UOsm), urine-specific gravity (USG), urine color (Ucolor), serum osmolality (SeOsm), serum arginine vasopressin (AVP), serum sodium (Na+), and thirst sensation in underhydrated athletes, using the body mass loss (BML) as the reference method.
METHODS: In this clinical trial (NCT05380089), a total of 38 athletes (17 females) with a regular low water intake (<35 mL/kg/day) were submitted to exercise-induced dehydration with a heat index of 29.8 ± 3.1 °C and an individualized running intensity (80-90% of first ventilatory threshold).
RESULTS: ROC curve analysis revealed significant discriminative abilities of SOsm, with AUC values of 0.76 at 1.5% BML, 0.75 at 1.75% BML, and 0.87 at 2% BML, while Na+ and SeOsm showed the highest AUC of 0.87 and 0.91 at 2% BML, respectively. SOsm showed high sensitivity at 1.5% of BML, while SeOsm and Na+ demonstrated high sensitivity at 2% of BML.
CONCLUSIONS: This study highlights SOsm as a potential indicator of hydration status across different levels of BML. Additionally, Na+ and SeOsm emerged as accurate dehydration predictors at 1.75% and 2% of BML. Notably, the accuracy of urinary indices and thirst sensation for detecting hydration may be limited.

UNASSIGNED: This cohort study aimed to explore the relationship between hydration status and the risk of diabetic kidney disease (DKD) as well as all-cause death in DKD patients.
UNASSIGNED: Weighted univariable and multivariable logistic regression models were used to explore the association between hydration status and DKD risk in diabetic population while weighted univariable and multivariable Cox regression models were used to identify the association between hydration status and all-cause mortality in DKD patients. Kaplan-Meier curve was plotted to present the survival probability of patients with different hydration status. Estimates were presented as odds ratio (OR), and hazard ratio (HR) with 95% confidence interval (CI).
UNASSIGNED: The mean follow-up time was 79.74 (±1.89) months. There were 2041 participants with DKD, and 2889 participants without. At the end of the follow-up, 965 participants were alive. The risk of DKD was increased as the increase of osmolarity level (OR = 1.07, 95%CI: 1.05-1.08). The elevated risk of DKD was observed in patients with impending dehydration (OR = 1.49, 95%CI: 1.19-1.85) or current dehydration (OR = 2.69, 95%CI: 2.09-3.46). The association between increased osmolarty level and elevated risk of all-cause mortality in DKD patients was statistically different (HR = 1.02, 95%CI: 1.01-1.03). Current dehydration was correlated with increased all-cause mortality risk in DKD patients (HR = 1.27, 95%CI: 1.01-1.61). Compared to DKD patients with normal hydration, the survival probability of DKD patients with current dehydration was significant lower (p < 0.001).
UNASSIGNED: Increased osmolarity level was associated with increased risk of DKD and elevated risk of all-cause mortality in DKD patients.

BACKGROUND: Neurostimulation/neurorecording are tools to study, diagnose, and treat neurologic/psychiatric conditions. Both techniques depend on volume conduction between scalp and excitable brain tissue. We examine how neurostimulation with TMS is affected by hydration status, a physiologic variable which can influence the volume of fluid spaces/cells, excitability and cellular/global brain functioning. Compared to dehydration, we expected rehydration to show signs of macroscopic and microscopic volume changes including decreased scalp-cortex distance (brain closer to stimulator) and astrocyte swelling-induced glutamate release.
METHODS: Normal healthy adult participants (32, 9 male) had common motor TMS measures taken in a repeated measures design from dehydrated (12-hour overnight fast/thirst) and rehydrated (identical dehydration protocol followed by rehydration with 1 L water in 1 hour) testing days. The target region was left primary motor cortex hand area. Response at the target muscle was recorded with electromyography. Urinalysis confirmed hydration status.
RESULTS: Motor hotspot shifted in half of participants. Motor threshold decreased in rehydration, indicating increased excitability. Even after re-dosing/re-localizing TMS to the new threshold/hotspot, rehydration still showed evidence of increased excitability: recruitment curve measures generally shifted upwards and SICF was increased. SICI, LICI, LICF, and CSP were relatively unaffected. The hydration perturbations were mild/subclinical, based on the magnitude/speed and urinalysis.
CONCLUSIONS: Motor TMS measures showed evidence of expected physiologic changes of osmotic challenges. Hydration may be a source of variability affecting techniques dependant on brain volumes/volume conduction. These concepts are important for researchers/clinicians using such techniques or dealing with the wide variety of disease processes involving water balance.

Diabetes, especially type 2 diabetes (T2D), poses an unprecedented challenge to global public health. Hydration status also plays a fundamental role in human health, especially in people with T2D, which is often overlooked. This study aimed to explore the longitudinal associations between hydration status and the risk of T2D among the Chinese population. This study used data from the large community-based Kailuan cohort, which included adults who attended physical examinations from 2006 to 2007 and were followed until 2020. A total of 71,526 participants who eventually met the standards were divided into five hydration-status groups based on their levels of urine specific gravity (USG). Multivariable and time-dependent Cox proportional hazards models were employed to evaluate the associations of baseline and time-dependent hydration status with T2D incidence. Restricted cubic splines (RCS) analysis was used to examine the dose-response relationship between hydration status and the risk of T2D. Over a median 12.22-year follow-up time, 11,804 of the participants developed T2D. Compared with the optimal hydration-status group, participants with dehydration and severe dehydration had a significantly increased risk of diabetes, with adjusted hazard ratios (95% CI) of 1.30 (1.04-1.63) and 1.38 (1.10-1.74). Time-dependent analyses further confirmed the adverse effects of impending dehydration, dehydration, and severe dehydration on T2D incidence by 16%, 26%, and 33% compared with the reference group. Inadequate hydration is significantly associated with increased risks of T2D among Chinese adults. Our findings provided new epidemiological evidence and highlighted the potential role of adequate hydration status in the early prevention of T2D development.

OBJECTIVE: Both short and long sleep durations are associated with decreased kidney function; however, few studies have examined the relationship between sleep, hydration status, and plain water intake. This study aimed to assess the relationship between sleep quality, hydration status, and plain water intake in pregnant women.
METHODS: A cross-sectional study method was used to collect data from 380 pregnant women with regular examinations at the hospital between May 2019 and February 2021.
RESULTS: There were statistically significant differences in daily plain water intake (x2 = 14.118, p = 0.001), PSQI score (x2 = 77.708, p < 0.001), sleep duration (x2 = 67.569, p > 0.001), subjective sleep quality (x2 = 67.441, p = 0.001), time to fall asleep (x2 = 64.782, p < 001), sleep disorders (x2 = 70.853, p < 0.001), and daytime dysfunction (x2 = 38.441, p < 0.001) among different hydration status groups. Ordinal logistic regression results indicated that the intake of plain water ≥1500 mL/d (OR = 0.40, 95% CI = 0.24~0.67), good subjective sleep quality (OR = 0.15, 95% CI = 0.07~0.32), short time to fall asleep (OR = 0.32, 95% CI = 0.14~0.70), 8 h of sleep (OR = 0.06, 95% CI = 0.02~0.17), 6-7 h of sleep (OR = 0.19, 95% CI = 0.07~0.54), no sleep disturbance (OR = 0.31, 95% CI = 0.11~0.89), and high sleep efficiency (OR = 0.46, 95% CI = 0.03~0.79) were factors that were correlated with optimal hydration status. Sleep duration and daytime dysfunction partially mediated the effect of plain water intake on hydration status. The mediating effect of sleep duration was -0.036, accounting for 14.006% of the overall effect. The mediating effect of daytime dysfunction was -0.024, accounting for 9.459% of the overall effect.
CONCLUSIONS: The hydration status in pregnant women may be affected by daily plain water intake and sleep quality.

The association of hydration knowledge and health habits with hydration status and fluid intake is rarely examined. We sought to determine whether knowledge or physical health behaviors predict physiological hydration status and fluid intake. Ninety-six participants (59 female; 27 ± 10 year) completed the previously validated hydration survey. Participants then recorded total fluids consumed (TFC), collected urine, and tracked void frequency for 24 h. Hydration status was assessed via 24 h urine specific gravity (USG) and osmolality (Uosm). Health behaviors included self-reported physical activity, BMI, smoking, alcoholic drinking, and sleep status. TFC was significantly correlated with 24 h USG (r = -0.390; p < 0.001), Uosm (r = -0.486; p < 0.001), total urine volume (r = 0.675; p < 0.001), and void frequency (r = 0.518; p < 0.001). Hydration knowledge was not correlated with 24 h USG (r = 0.085; p = 0.420), Uosm (r = 0.087; p = 0.419), urine total volume (r = 0.019; p = 0.857), void frequency (r = 0.030; p = 0.771), or TFC (r = 0.027; p = 0.813). Hydration knowledge did not predict 24 h USG (LR+ = 1.10; LR- = 0.90), Uosm (LR+ = 0.81; LR- = 1.35), or TFC (LR+ = 1.00; LR- = 1.00). Health habits did not predict 24 h USG, Uosm, or TFC. In conclusion, self-reported 24 h diet and fluid log recording is comparable to hydration status verification via 24 h urine collection. Hydration knowledge and health habits are not related to, or predictive of, hydration status.

BACKGROUND: Water intake and hydration status may potentially influence maternal and child health. However, there is little research regarding this topic.
OBJECTIVE: This study aimed to investigate pregnant women\'s total fluid intake (TFI) levels, hydration status, and body composition and further explore their relationship with infant birth weight.
METHODS: A 7-day, 24 h fluid intake recorded was applied to determine participants\' TFI levels. Morning urine samples were collected and tested to evaluate their hydration status. Maternal body compositions in their third trimester and infant birth weights were measured.
RESULTS: A total of 380 participants completed the study. The TFI was insufficient for pregnant women during their third trimester (median = 1574 mL), with only 12.1% of participants meeting the recommended adequate fluid intake level for pregnant women living in China (1.7 L per day). With the increasing TFI values, the urine osmolality decreased, which showed statistical significance among the four groups (χ2 = 22.637, p < 0.05). The participants displayed a poor hydration status. Meanwhile, the percentage of participants who were in dehydrated status decreased (χ2 = 67.618, p < 0.05), while body water content and basal metabolic rate increased with the increase in TFI levels (χ2 = 20.784, p < 0.05; χ2 = 14.026, p < 0.05). There were positive linear relationships between plain water intake, the basal metabolic rate of pregnant women and their infant birth weight (SE = 0.153, p < 0.05; SE = 0.076, p < 0.05).
CONCLUSIONS: Water intake was insufficient, and poor hydration status was common among pregnant women in China. There may be potential relationships between plain water intake, basal metabolic rate, and infant birth weight.

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Cajuína is a processed drink derived from cashew and is widely consumed in the northeast region of Brazil. This study evaluated the effect of a cajuína-based hydroelectrolytic drink on the aerobic performance and hydration status of recreational runners. Seventeen males (31.9 ± 1.6 years, 51.0 ± 1.4 ml/kg/min) performed three time-to-exhaustion running sessions on a treadmill at 70% VO2max, ingesting cajuína hydroelectrolytic drink (CJ), high carbohydrate commercial hydroelectrolytic drink (CH) and mineral water (W) every 15 min during the running test. The participants ran 80.3 ± 8.4 min in CJ, 70.3 ± 6.8 min in CH and 71.8 ± 6.9 min in W, with no statistical difference between procedures. Nevertheless, an effect size of η2 = 0.10 (moderate) was observed. No statistical difference was observed in the concentrations of sodium, potassium, and osmolality in both serum and urine between the three conditions. However, the effect size was moderate (urine sodium) and high (serum sodium, potassium, and osmolality). Urine specific gravity, sweating rate and heart rate were not significantly different between drinks. The cajuína-based hydroelectrolytic drink promotes similar effects compared to commercial hydroelectrolytic drink and water, considering specific urine gravity, heart rate, sweating, and time to exhaustion in recreational runners.