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THE EFFECT OF THIRST ON SLEEPINESS AND VISUOMOTOR REACTION TIME

Abstract

BACKGROUND: Many individuals do not consume an appropriate amount of fluid. This low fluid intake leads to increased levels of thirst and hypohydration. The sensation of thirst influences areas of the brain that are associated with reaction time performance. Additionally, low fluid intake often results in elevated levels of arginine vasopressin, which exacerbates mood and alertness decrements. The purpose of this study was to determine the effect of fluid intake and thirst perception on perceived sleepiness levels and visuomotor reaction time. METHODS: College age males (n = 12; age = 21 ± 1 yr) participated in this randomized, counterbalanced, cross-over study. Participants completed three visits with different conditions: 1) euhydrated and received no fluid throughout the trial, 2) following 12-hour fluid restriction and received no fluid throughout the trial, and 3) following 12-hour fluid restriction and received 200 mL during the trial between two reaction time tests. Upon arrival, all hydration was assessed via urine specific gravity and urine color. Participants also recorded thirst sensation at various time points throughout the trial. Participants rated their level of perceived sleepiness and completed central vision and peripheral vision reaction time tests on the Dynavision twice throughout each trial. RESULTS: Sleepiness was not different between trials (p >0.05). Thirst sensation was significantly higher at the start of the hypohydrated trials than the euhydrated trial. Thirst sensation was significantly lower following the 200 mL of fluid intake in the hypohydrated trial (p < 0.05). Central and peripheral vision reaction time was improved following fluid intake in the hypohydrated condition (p < 0.05) but not in the other two trials. CONCLUSION: Thirst sensation, independent of hydration status, appears to diminish reaction time performance.

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