Armstrong, L. E., Ganio, M. S., Lee, E. C., McDermott, B. P., Klau, J. F., Yamamoto, L. M., Marzano, S., Lopez, R., Beasley, K. N., Jiminez, L., Le Bellego, L., Chevillotte, E., Casa, D. J., & Lieberman, H. R. (June 02, 2010). Degraded cognitive performance and increased fatigue in men following mild dehydration at 1.59% body mass loss. Presentation 1686 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

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This study assessed the effects of mild dehydration on cognitive performance and mood of healthy young males (N = 26). Ss participated in three placebo-controlled, randomized, single-blind, repeated measure trials (9.8 hours each, separated by more than four days) designed to produce different hydration states: exercise-heat dehydration (three 40-min treadmill walks at 5.6 km/h, 5% grade, 28°C), exercise-heat dehydration plus diuretic ingestion (40 mg furosemide), and control (exercise, body mass maintained by water intake). A comprehensive computerized 6-task cognitive test battery, Profile of Mood States (POMS) questionnaire, and visual analog scales (headache, concentration, task difficulty) were administered during each trial.

The exercise-heat dehydration and exercise-heat dehydration plus diuretic ingestion trials produced >1% body mass loss compared to the control trial. Dehydration degraded specific aspects of cognitive performance: visual working memory response latency was slowed and errors increased on visual vigilance. Fatigue, as measured by the POMS, increased due to dehydration. Resting gastrointestinal temperature was not altered by dehydration but plasma osmolality increased. [In a similar study, greater effects of mild dehydration (-1.39%) on mood (POMS) and visual analog scales were observed in women than men. The POMS factors of fatigue, tension, vigor, confusion, and concentration deteriorated, while headache and perceived task difficulty increased only in women.] This study’s findings suggest that when compared to women men are less able to detect the effects of mild dehydration on cognitive states. This may be due to the fact that men had smaller increases of gastrointestinal temperature and plasma osmolality than women, even though their level of dehydration was slightly greater.

Implication. Mild dehydration of 1.59% in men has subtle adverse effects on visual working memory, visual vigilance, and perception of fatigue. Other cognitive test battery variables are not affected. When compared to the responses of women from another study, females are affected in more psychological variables than men.

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