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1.
Front Nutr ; 6: 161, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31681787

RESUMO

Purpose: The purpose of this observational study was to examine the incidence of exercise-associated hyponatremia (EAH) in a 246-km continuous ultra-marathon. Methods: Over 2 years, 63 male finishers of the annual Spartathlon ultra-marathon foot race from Athens to Sparta, Greece were included in the data analysis. A blood sample was drawn from an antecubital vein the day before the race as well as within 15 min post-race and analyzed for sodium concentration. During the second year of data collection, blood was also drawn at the 93-km checkpoint (n = 29). Height and weight were measured pre and post-race. Results: Mean race time of all subjects was 33 ± 3 h with a range of 23.5 and 36.0 h. Of the 63 finishers recruited, nine began the race with values indicative of mild hyponatremia. Seven runners were classified as hyponatremic at the 93-km checkpoint, three of whom had sodium levels of severe hyponatremia. After the race, 41 total finishers (65%) developed either mild (n = 27, 43%) or severe hyponatremia (n = 14, 22%). Mean change in bodyweight percentage and serum sodium from pre-race to post-race was -3.6 ± 2.7% (-2.5 ± 1.9 kg) and -6.6 ± 5.6 mmol·L-1, respectively. Pre-race serum sodium level was not a significant predictor of post-race serum sodium levels (ß = 0.08, R 2 = 0.07, P = 0.698), however, there was a significant negative association between change in bodyweight percentage and post-race serum sodium concentration (ß = -0.79, R 2 = 0.29, P = 0.011). Conclusion: The incidence of EAH of 52 and 65%, when excluding or including these individuals with pre-race hyponatremia, was the highest reported in current literature.

2.
Eur J Clin Nutr ; 2019 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-31624367

RESUMO

BACKGROUND/OBJECTIVES: While daily hydration is best assessed in 24-h urine sample, spot sample is often used by health care professionals and researchers due to its practicality. However, urine output is subject to circadian variation, with urine being more concentrated in the morning. It has been demonstrated that afternoon spot urine samples are most likely to provide equivalent urine concentration to 24-h urine samples in adults. The aim of the present study was to examine whether urine osmolality (UOsm) assessed from a spot urine sample in specific time-windows was equivalent to 24-h UOsm in free-living healthy children. SUBJECTS/METHODS: Among 541 healthy children (age: 3-13 years, female: 45%, 77% non-Hispanic white, BMI:17.7 ± 4.0 kg m-2), UOsm at specific time-windows [morning (0600-1159), early afternoon (1200-1559), late afternoon (1600-1959), evening (2000-2359), overnight (2400-0559), and first morning] was compared with UOsm from the corresponding pooled 24-h urine sample using an equivalence test. RESULTS: Late afternoon (1600-1959) spot urine sample UOsm value was equivalent to the 24-h UOsm value in children (P < 0.05; mean difference: 62 mmol kg-1; 95% CI: 45-78 mmol kg-1). The overall diagnostic ability of urine osmolality assessed at late afternoon (1600-1959) to diagnose elevated urine osmolality on the 24-h sample was good for both cutoffs of 800 mmol kg-1 [area under the curve (AUC): 87.4%; sensitivity: 72.6%; specificity: 90.5%; threshold: 814 mmol kg-1] and 500 mmol kg-1 (AUC: 83.5%; sensitivity: 75.0%; specificity: 80.0%; threshold: 633 mmol kg-1). CONCLUSION: These data suggest that in free-living healthy children, 24-h urine concentration may be approximated from a late afternoon spot urine sample. This data will have practical implication for health care professionals and researchers.

3.
Am J Clin Nutr ; 110(6): 1344-1352, 2019 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-31562496

RESUMO

BACKGROUND: Epidemiological studies in humans show increased concentrations of copeptin, a surrogate marker of arginine vasopressin (AVP), to be associated with increased risk for type 2 diabetes. OBJECTIVES: To examine the acute and independent effect of osmotically stimulated AVP, measured via the surrogate marker copeptin, on glucose regulation in healthy adults. METHODS: Sixty subjects (30 females) participated in this crossover design study. On 2 trial days, separated by ≥7 d (males) or 1 menstrual cycle (females), subjects were infused for 120 min with either 0.9% NaCl [isotonic (ISO)] or 3.0% NaCl [hypertonic (HYPER)]. Postinfusion, a 240-min oral-glucose-tolerance test (OGTT; 75 g) was administered. RESULTS: During HYPER, plasma osmolality and copeptin increased (P < 0.05) and remained elevated during the entire 6-h protocol, whereas renin-angiotensin-aldosterone system hormones were within the lower normal physiological range at the beginning of the protocol and declined following infusion. Fasting plasma glucose did not differ between trials (P > 0.05) at baseline and during the 120 min of infusion. During the OGTT the incremental AUC for glucose from postinfusion baseline (positive integer) was greater during HYPER (401.5 ± 190.5 mmol/L·min) compared with the ISO trial (354.0 ± 205.8 mmol/L·min; P < 0.05). The positive integer of the AUC for insulin during OGTT did not differ between trials (HYPER 55,850 ± 36,488 pmol/L·min compared with ISO 57,205 ± 31,119 pmol/L·min). Baseline values of serum glucagon were not different between the 2 trials; however, the AUC of glucagon during the OGTT was also significantly greater in HYPER (19,303 ± 3939 ng/L·min) compared with the ISO trial (18,600 ± 3755 ng/L·min; P < 0.05). CONCLUSIONS: The present data indicate that acute osmotic stimulation of copeptin induced greater hyperglycemic responses during the oral glucose challenge, possibly due to greater glucagon concentrations.This study was registered at clinicaltrials.gov as NCT02761434.


Assuntos
Glicemia/metabolismo , Cloreto de Sódio/administração & dosagem , Vasopressinas/metabolismo , Adulto , Estudos Cross-Over , Feminino , Glucagon/sangue , Teste de Tolerância a Glucose , Glicopeptídeos/sangue , Humanos , Insulina/sangue , Masculino , Pessoa de Meia-Idade , Concentração Osmolar , Osmose , Plasma/química , Cloreto de Sódio/análise
4.
Scand J Med Sci Sports ; 29(5): 686-695, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30659665

RESUMO

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.


Assuntos
Desempenho Atlético/fisiologia , Ciclismo/fisiologia , Desidratação/fisiopatologia , Temperatura Alta , Adulto , Glicemia/análise , Proteínas Sanguíneas/análise , Peso Corporal , Estudos Cross-Over , Ergometria , Humanos , Ácido Láctico/sangue , Masculino , Percepção , Gravidade Específica , Sudorese , Urinálise , Adulto Jovem
5.
Med Sci Sports Exerc ; 50(8): 1697-1703, 2018 08.
Artigo em Inglês | MEDLINE | ID: mdl-29509643

RESUMO

PURPOSE: The aim of the present study was to examine the effect of dehydration on exercise performance independently of thirst with subjects blinded of their hydration status. METHODS: Seven male cyclists (weight, 72 ± 9 kg; body fat, 14% ± 6%; peak oxygen uptake, 59.4 ± 6 mL·kg·min) exercised for 2 h on a cycle ergometer at 55% peak oxygen uptake, in a hot-dry environment (35°C, 30% relative humidity), with a nasogastric tube under euhydrated-non-thirst (EUH-NT) and dehydrated-non-thirst (DEH-NT) conditions. In both trials, thirst was matched by drinking 25 mL of water every 5 min (300 mL·h). In the EUH-NT trial, sweat losses were fully replaced by water via the nasogastric tube (calculated from the familiarization trial). After the 2 h of steady state, the subjects completed a 5-km cycling time trial at 4% grade. RESULTS: Body mass loss for the EUH-NT and DEH-NT after the 2 h was -0.2% ± 0.6% and -2.2% ± 0.4%, whereas after the 5-km time trial, it was -0.7% ± 0.5% and 2.9% ± 0.4%, respectively. Thirst (35 ± 30 vs 42 ± 31 mm) and stomach fullness (46 ± 21 vs 35 ± 20 mm) did not differ at the end of the 2 h of steady state between EUH-NT and DEH-NT trials (P > 0.05). Subjects cycled faster during the 5-km time trial in the EUH-NT trial compared with the DEH-NT trial (23.2 ± 1.5 vs 22.3 ± 1.8 km·h, P < 0.05), by producing higher-power output (295 ± 29 vs 276 ± 29 W, P < 0.05). During the 5-km time trial, core temperature was higher in the DEH-NT trial (39.2°C ± 0.7°C) compared with the EUH-NT trial (38.8°C ± 0.2°C; P > 0.05). CONCLUSIONS: These data indicated that hypohydration decreased cycling performance and impaired thermoregulation independently of thirst, while the subjects were unaware of their hydration status.


Assuntos
Desempenho Atlético/fisiologia , Ciclismo/fisiologia , Desidratação/fisiopatologia , Exercício Físico/fisiologia , Sede , Regulação da Temperatura Corporal , Humanos , Intubação Gastrointestinal , Masculino , Percepção , Método Simples-Cego
6.
Eur J Clin Nutr ; 72(3): 420-427, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29238038

RESUMO

BACKGROUND/OBJECTIVES: Children consume various fluids to meet dietary water intake needs. However, the contribution of different fluid types on hydration is unclear. The purpose of this study was to develop fluid intake patterns and examine their association with hydration, as indicated by 24-h urine osmolality. SUBJECTS/METHODS: Two hundred ten (105 girls) healthy children (height: 1.49 ± 0.13 m, weight: 43.4 ± 12.6 kg, body fat: 25.2 ± 7.8%) recorded their fluid intake for two consecutive days, and collected their urine for 24-h during the 2nd day, while conducting their normal daily activities. Urine samples were analyzed for specific gravity and osmolality. Factor analysis with principal components method was applied to extract dietary patterns from six fluid groups. Linear regression analysis evaluated the associations between the extracted dietary patterns and hydration based on 24-h urine osmolality. RESULTS: The analysis revealed the following six components: 1, characterized by consumption of milk and fresh juice, but not packaged juice; 2, by regular soda and other drinks, but not water; 3, by fresh juice and other drinks; 4, by packaged juice, but not regular soda; 5, by water and milk; and 6, by fresh juice. Component 5 was negatively correlated with urine osmolality (P = 0.001) indicating better hydration, whereas component 2 was positively correlated with urine osmolality (P = 0.001). CONCLUSIONS: A drinking pattern based on water and milk was associated with better hydration, as indicated by lower urine osmolality, whereas drinking regular soda and other drinks but not water was associated with inferior hydration.


Assuntos
Bebidas/estatística & dados numéricos , Água Corporal/fisiologia , Dieta/estatística & dados numéricos , Adolescente , Animais , Criança , Estudos de Coortes , Desidratação/urina , Feminino , Humanos , Masculino , Leite , Concentração Osmolar , Gravidade Específica , Urinálise , Água
7.
Int J Sport Nutr Exerc Metab ; 28(1): 75-81, 2018 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-29035599

RESUMO

The purpose of this article is to assess the hydration status of elite young sailing athletes during World Championship competition. Twelve young, elite, male, Laser Class sailors (age: 15.8 ± 1.1 y, height: 1.74 ± 0.1 m, weight: 65.1 ± 1.5 kg, body fat: 12.5 ± 3.1%, training experience: 7.0 ± 1.2 y) participated in this descriptive study. After three-day baseline bodyweight measurements, hydration status was assessed via pre- and post-race body weights, urine-specific gravity, and thirst ratings via a visual analog scale during four consecutive days of racing. Measurements and data collection took place at the same time each racing day, with mean environmental temperature, humidity, and wind speed at 23.0 ± 0.8°C, 64-70%, and 9 ± 1 knots, respectively. Average racing time was 130 ± 9 min. Body weight was significantly decreased following each race-day as compared to prerace values (Day 1: -1.1 ± 0.2, Day 2: -2.5 ± 0.1, Day 3: -2.8 ± 0.1, and Day 4: -3.0 ± 0.1% of body weight; p < 0.05). The participants exhibited dehydration of -2.9 ± 0.2 and -5.8 ± 0.2% of body weight before and after the fourth racing day as compared to the three-day baseline body weight. Urine-specific gravity (pre-post → Day 1: 1.014-1.017; Day 2: 1.019-1.024; Day 3: 1.021-1.026; Day 4: 1.022-1.027) and thirst (pre-post → Day 1: 2.0-5.2; Day 2: 3.2-5.5; Day 3: 3.7-5.7; Day 4: 3.8-6.8) were also progressively and significantly elevated throughout the four days of competition. The data revealed progressive dehydration throughout four consecutive days of racing as indicated by decreased body weight, elevated urine concentration, and high thirst.


Assuntos
Atletas , Desidratação , Esportes/fisiologia , Sede , Perda de Peso , Peso Corporal , Humanos , Masculino , Navios , Urinálise , Adulto Jovem
8.
Front Nutr ; 4: 40, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28868290

RESUMO

BACKGROUND: Low levels of caffeine ingestion do not induce dehydration at rest, while it is not clear if larger doses do have an acute diuretic effect. The aim of the present investigation was to examine the acute effect of low and high levels of caffeine, via coffee, on fluid balance in habitual coffee drinkers (at least one per day) at rest. METHODS: Ten healthy adults (eight males and two females; age: 27 ± 5 years, weight: 89.5 ± 14.8 kg, height: 1.75 ± 0.08 m, and body mass index: 29.1 ± 4.4 kg m-2) ingested 200 mL of water (W), coffee with low caffeine (3 mg kg-1, LCAF), or coffee with high caffeine (6 mg kg-1, HCAF) on three respective separate occasions. All sessions were performed at 09:00 in the morning in a counterbalanced, crossover manner, at least 5 days apart. Subjects remained in the laboratory while urine samples were collected every 60 min for 3 h post ingestion. RESULTS: Absolute caffeine consumption was 269 ± 45 and 537 ± 89 mg for the LCAF and HCAF, respectively. Coffee ingestion at the HCAF trial induced greater diuresis during the 3-h period (613 ± 101 mL, P < 0.05), when compared to W (356 ± 53 mL) and LCAF (316 ± 38 mL). In addition, cumulative urinary osmotic excretion was significantly greater in the HCAF (425 ± 92 mmol, P < 0.05), as compared to the W (249 ± 36 mmol) and LCAF (177 ± 16 mmol) trials. CONCLUSION: The data indicate that caffeine intake of 6 mg kg-1 in the form of coffee can induce an acute diuretic effect, while 3 mg kg-1 do not disturb fluid balance in healthy casual coffee drinking adults at rest.

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