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Ad libitum water consumption prevents exercise-associated hyponatremia and protects against dehydration in soldiers performing a 40-km route-march.
Mil Med Res. 2019 01 25; 6(1):1.MM

Abstract

BACKGROUND

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 post-exercise sodium level completed the march in 08:38. He drank 800 ml/h, lost 2% body mass, and demonstrated (pre-post) 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.

Authors+Show Affiliations

Movement Physiology Research Laboratory, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. heinrichwnolte@gmail.com.Division Biokinetics and Sport Science, Department of Physiology, University of Pretoria, Pretoria, South Africa.Division of Kinesiology, Wayne State University, Detroit, MI, USA.

Pub Type(s)

Journal Article
Observational Study
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

30678725

Citation

Nolte, Heinrich W., et al. "Ad Libitum Water Consumption Prevents Exercise-associated Hyponatremia and Protects Against Dehydration in Soldiers Performing a 40-km Route-march." Military Medical Research, vol. 6, no. 1, 2019, p. 1.
Nolte HW, 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. Mil Med Res. 2019;6(1):1.
Nolte, H. W., Nolte, K., & Hew-Butler, T. (2019). Ad libitum water consumption prevents exercise-associated hyponatremia and protects against dehydration in soldiers performing a 40-km route-march. Military Medical Research, 6(1), 1. https://doi.org/10.1186/s40779-019-0192-y
Nolte HW, 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. Mil Med Res. 2019 01 25;6(1):1. PubMed PMID: 30678725.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Ad libitum water consumption prevents exercise-associated hyponatremia and protects against dehydration in soldiers performing a 40-km route-march. AU - Nolte,Heinrich W, AU - Nolte,Kim, AU - Hew-Butler,Tamara, Y1 - 2019/01/25/ PY - 2018/10/25/received PY - 2019/01/08/accepted PY - 2019/1/26/entrez PY - 2019/1/27/pubmed PY - 2019/3/21/medline KW - Arginine vasopressin KW - Electrolyte balance KW - Exercise-associated hyponatremia KW - Fluid balance KW - Military KW - Serum sodium concentration SP - 1 EP - 1 JF - Military Medical Research JO - Mil Med Res VL - 6 IS - 1 N2 - BACKGROUND: 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 post-exercise sodium level completed the march in 08:38. He drank 800 ml/h, lost 2% body mass, and demonstrated (pre-post) 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. SN - 2054-9369 UR - https://www.unboundmedicine.com/medline/citation/30678725/Ad_libitum_water_consumption_prevents_exercise_associated_hyponatremia_and_protects_against_dehydration_in_soldiers_performing_a_40_km_route_march_ L2 - https://mmrjournal.biomedcentral.com/articles/10.1186/s40779-019-0192-y DB - PRIME DP - Unbound Medicine ER -