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EFFECTS OF QUENCHING THIRST VERSUS FULL FLUID REPLENISHMENT ON MOOD AND COGNITIVE CHANGES AFTER MILD HYPOHYDRATION

Abstract

Brian Hack, Hyun Gyu Suh, Mindy Millard-Stafford, FACSM. Georgia Institute of Technology, Atlanta, GA.

Dehydration impairs mood and sustained attention; however, evidence regarding the time course that rehydration reverses such effects is limited. Furthermore, whether assuaging thirst reverses cognitive deficits is unclear. Our purpose was to examine effects of partial rehydration (quenching thirst) compared to full rehydration (restoring fluid balance) on cognitive changes induced by exercise-induced dehydration. METHODS: Fifteen physically active men (age: 23.6±4.4 y; weight: 73.7±7.9 kg) participated in a dehydration-rehydration protocol. Mild-hypohydration [-1.7±0.3% change in body mass (%ΔBM)] was achieved via cycling in the heat (35°C; 40%RH) followed by 30 min rehydration (restoring >100% BM). Flanker cognitive task and Brunel Mood scale were administered at baseline (BASE), dehydration (DEH), partial rehydration replacing 50% BM loss (PAR), and immediately following full fluid replacement (FULL0) through 180 min (FULL180). RESULTS: DEH increased (P<0.05) thirst from BASE (4.6 ± 0.7 to 6.2 ± 0.6 cm) but PAR (3.5 ± 1.5 cm) attenuated thirst with no additional changes through FULL180 (3.5 ± 1.6 cm). Plasma osmolality decreased (P<0.05) from DEH to FULL0 (296.5 ± 3.6 to 294.5 ± 2.8 mmol/kg) but continued lower by FULL60 (291.0 ± 3.0 mmol/kg). Copeptin also decreased (P<0.05) from DEH to FULL0 (22.1 ± 9.1 to 14.5 ± 7.3 pmol/L) and continued lower by FULL60 (7.7 ± 3.5 pmol/L). Compared to DEH, FULL0 restored (P<0.05) %ΔBM (0.1 ± 0.3%) similar to BASE. However, %ΔBM became lower (P<0.05) than BASE by FULL60 (-0.5 ± 0.3%) through FULL180 (-1.0 ± 0.4%) although %ΔBM remained above DEH. Flanker incongruent reaction time decreased (P<0.05) from BASE (0.46±0.02s) due to DEH (0.42 ± 0.02s) and persisted through FULL180 (0.42 ± 0.02s). Accuracy (%correct) decreased (P<0.05) from BASE (93.7 ± 4.7%) to DEH (87.0 ± 6.7%) and remained lower through FULL180 (87.6 ± 4.0%). Fatigue ratings decreased (P<.05) from DEH (6.9 ± 3.1) with PAR (4.7 ± 2.6) and remained lower through FULL180 (3.2 ± 3.5) similar to BASE (3.1 ± 1.7). CONCLUSION: Partial rehydration attenuated thirst and improved perceived fatigue but did not reverse cognitive changes. Fully restoring fluid balance after dehydration also did not reverse cognitive changes. Effects of fluid imbalance versus thirst on cognitive deficits remains unclear. Funded by a grant from The Coca-Cola Company, Atlanta, GA.

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