Mild dehydration impairs cognitive performance and mood of men

The present study assessed the effects of mild dehydration on cognitive performance and mood of young males. A total of twenty-six men (age 20.0 (SD 0.3) years) participated in three randomised, single-blind, repeated-measures trials: exercise-induced dehydration plus a diuretic (DD; 40 mg furosemide); exercise-induced dehydration plus placebo containing no diuretic (DN); exercise while maintaining euhydration plus placebo (EU; control condition). Each trial included three 40 min treadmill walks at 5.6 km/h, 5% grade in a 27.7 degrees C environment. A comprehensive computerised six-task cognitive test battery, the profile of mood states questionnaire and the symptom questionnaire (headache, concentration and task difficulty) were administered during each trial. Paired t tests compared the DD and DN trials resulting in >1% body mass loss (mean 1.59 (SD 0.42) %) with the volunteer's EU trial (0.01 (SD 0.03) %). Dehydration degraded specific aspects of cognitive performance: errors increased on visual vigilance (P=0.048) and visual working memory response latency slowed (P=0.021). Fatigue and tension/anxiety increased due to dehydration at rest (P=0.040 and 0.029) and fatigue during exercise (P=0.026). Plasma osmolality increased due to dehydration (P<0.001) but resting gastrointestinal temperature was not altered (P=0.238). In conclusion, mild dehydration without hyperthermia in men induced adverse changes in vigilance and working memory, and increased tension/anxiety and fatigue.