Hypervolemia induced by fluid ingestion at rest: effect of sodium concentration
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Sodium drink is used as a countermeasure against body fluid loss. However, high concentrations of sodium may cause gastrointestinal upset (e.g., diarrhea). We sought to determine the sodium concentration that induces hypervolemia with a minimal risk of gastrointestinal disturbance.
Eight healthy active males rested in a chair and ingested a given amount (16−17 ml kg body mass−1) of water (W) or solution containing 60, 120 or 180 mmol l−1 Na+ (60, 120 and 180Na trials) in 6 equal portions at 10 min intervals. To standardize their hydration status, subjects consumed the same meal and water 2 h before each trial. Drink trials were performed on separate days, and the order was randomized. The change in plasma volume (PV) from pre-drink status was estimated from the hemoglobin concentration and hematocrit every 30 min for 150 min after initiation of drinking.
Subjects began trials in a euhydrated state, as reflected by their plasma osmolality (in mmol l−1: W, 289.4 ± 1.4; 60Na, 287.0 ± 3.5; 120Na, 287.6 ± 2.3; 180Na, 288.9 ± 3.3). At 120 min, PV had not increased from the pre-drink value in the W (−0.8 ± 4.5 %) or 60Na (2.4 ± 4.9 %) trials, but it increased to similar degrees in the 120Na (7.2 ± 4.6 %) and 180Na (9.4 ± 6.6 %) trials. No diarrhea was reported in the W or 60Na trials, but it was reported in the 120Na (n = 1) and 180Na (n = 6) trials.
Beverages containing 120 mmol l−1 Na+ induce hypervolemia with a minimum incidence of gastrointestinal problems.
KeywordsHyperhydration Blood Extracellular fluid Fluid balance Fluid intake
Analysis of variance
We would like to sincerely thank the volunteer subjects for participating in this study. We also greatly appreciate the Dr. William Goldman for english editing and critical comments. This study was supported by grants from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
Conflict of interest
There are no conflicts of interest in the present study.
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