The effect of fluid composition on rehydration following heat and exercise-induced dehydration
Douglas S. King
Rick L. Sharp
The influence of fluid composition on rehydration effectiveness was assessed following exercise and heat (65°C) exposure that produced a 2.6% body weight loss. In a randomized cross-over design, 18 subjects rehydrated for 3 h with water (H2O), and broths containing various sodium concentrations (LO: 31.5 mmol/l; MED: 109.5 mmol/l; HI: 159.5 mmol/l). Beverages were given in equal volumes every 20 min for a total volume equal to the body weight loss during dehydration. Significant differences (p < 0.05) among the treatments were determined using ANOVA. Body weight recovery was higher in MED compared witb LO (73 ± 3% vs 61 ± 4%). Plasma volume recovery was higher in MED (105 ± 1%) and HI (104 ± 2%) compared with H2O (97 ± 2%). Urine volume was higher in H2O (351 ± 57 ml) and LO (379 ± 29 ml) compared with MED (229 ± 18 ml) and HI (195 ± 21 ml). Plasma osmolality was higher in HI and MED compared with H2O, while the plasma sodium concentration was higher in LO, MED, and HI compared with H2O. The plasma potassium concentration was higher in LO compared with all other beverages;In the second study, 30 subjects were studied during 2 h of rehydration after a 2.5% body weight loss. In a randomized cross-over design, subjects rehydrated with water (H2O), chicken broth (CB: Na = 109.5; K = 25.3 mmol/l), a carbohydrate-electrolyte drink (CE: Na = 16.0; K = 3.3 mmol/l), and chicken noodle soup (SOUP: Na = 333.8; K = 13.7 mmol/l). Subjects ingested 175 ml at the start of rehydration and 20 min later; water was given every 20 min thereafter for a total volume equal to body weight loss during dehydration. Plasma volume recovery was greater in SOUP (99 ± 1%) and CB (98 ± 1%) compared with H2O (94 ± 1%). Urine volume was greater in CE (310 ± 30 ml) compared with CB (188 ± 20 ml). Urine osmolality was higher in CB and SOUP compared with CE. Urinary sodium concentration was higher in SOUP and CB compared with CE and H2O. These results suggest that including sodium in rehydration beverages improves whole body and plasma volume restoration.