Ad libitum water consumption prevents exercise-associated hyponatremia and protects against dehydration in soldiers performing a 40-km route-march

dc.contributor.authorNolte, Heinrich W.
dc.contributor.otherauthorNolte, Kim
dc.contributor.otherauthorHew-Butler, Tamara
dc.date.accessioned2025-07-08T12:45:41Z
dc.date.issued2019-01
dc.description.abstractBackground: It remains unclear if ad libitum water drinking, as a hydration strategy, prevents exercise-associated hyponatremia (EAH) during prolonged exercise. The aim of this study was to determine the incidence of EAH within the broader context of fluid regulation among soldiers performing a 40-km route-march ingesting water ad libitum. Methods: Twenty-eight healthy male soldiers participated in this observational trial. Pre- and post-exercise body mass, blood and urine samples were collected. Blood samples were assessed for serum sodium ([Na+]), glucose, creatinine, urea nitrogen (BUN), plasma osmolality, creatine kinase (CK), and plasma arginine vasopressin (AVP) concentrations. Plasma volume (PV) was calculated using hematocrit and hemoglobin. Urine samples were analyzed for osmolality and [Na+]. Water intake was assessed by weighing bottles before, during and after the march. The mean relative humidity was 55.7% (21.9–94.3%) and the mean dry bulb temperature was 27.1 °C (19.5 °C - 37.0 °C) during the exercise. Results: Twenty-five soldiers (72 ± 10 kg) (Mean ± SD) completed the march in 09:11 ± 00:43 (hr:min). Participants consumed 736 ± 259 ml/h of water and lost 2.8 ± 0.9 kg (4.0% ± 1.4%, P < 0.05) of body mass. Significant (pre-march vs. post-march; P < 0.05) decreases in serum [Na+] (141 mmol/L vs. 136 mmol/L), plasma osmolality (303 mOsmol/kg H2O vs. 298 mOsmol/kg H2O), and serum creatinine (111 μmol/L vs. 101 μmol/L) and urine [Na+] (168 mmol/L vs. 142 mmol/L), as well as significant increases in plasma AVP (2 pg/ml vs. 11 pg/ml), plasma CK (1423 U/L vs. 3894 U/L) and urine osmolality (1035 mOsmol/kg H2O vs. 1097 mOsmol/kg H2O) were found. The soldier (72 kg) with the lowest postexercise sodium level completed the march in 08:38. He drank 800 ml/h, lost 2% body mass, and demonstrated (prepost) increases in plasma osmolality (294–314 mOsmol/kg H2O), BUN (20–30 mg/dl), AVP (2–16 pg/ml) and PV (41%). His urine osmolality decreased from 1114 mOsmol/kg H2O to 1110 mOsmol/kg H2O. No participants finished the route-march with a serum [Na+] indicating hypernatremia (range, 134–143 mmol/L). Conclusions: Ad libitum drinking resulted in 4% body mass loss with a 2 mmol/L serum [Na+] reduction in conjunction with high urine osmolality (> 1000 mOsmol/kg H2O) and plasma AVP. No single hydration strategy likely prevents EAH, but hypernatremia (cellular dehydration) was not seen despite > 2% body mass losses and high urine osmolality.
dc.description.submitterPM2025
dc.facultyFaculty of Health Sciences
dc.identifier.citationNolte, H.W., Nolte, K. & Hew-Butler, T. Ad libitum water consumption prevents exercise-associated hyponatremia and protects against dehydration in soldiers performing a 40-km route-march. Military Med Res 6, 1 (2019). https://doi.org/10.1186/s40779-019-0192-y
dc.identifier.issn2054-9369 (online)
dc.identifier.other10.1186/s40779-019-0192-y
dc.identifier.urihttps://hdl.handle.net/10539/45342
dc.journal.titleMilitary Medical Research
dc.language.isoen
dc.publisherBioMed Central
dc.relation.ispartofseriesVol.6; No.1
dc.rights© The Author(s). 2019 Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License.
dc.schoolSchool of Physiology
dc.subjectSerum sodium concentration
dc.subjectExercise-associated hyponatremia
dc.subjectArginine vasopressin
dc.subjectFluid balance
dc.subjectElectrolyte balance
dc.subjectMilitary
dc.subject.primarysdgSDG-3: Good health and well-being
dc.titleAd libitum water consumption prevents exercise-associated hyponatremia and protects against dehydration in soldiers performing a 40-km route-march
dc.typeArticle

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