Effects of fluid ingestion on cognitive function after heat stress or exercise-induced dehydration

This study investigated the effects of heat exposure, exercise-induced dehy dration and fluid ingestion on cognitive performance. Seven healthy men, un acclimatized to heat, were kept euhydrated or were dehydrated by controlled passive exposure to heat (H, two sessions) or by treadmill exercise (E, tw o sessions) up to a weight loss of 2.8%. On completion of a 1-h recovery pe riod, the subjects drank a solution containing 50 g l(-1) glucose and 1.34 g l(-1) NaCl in a volume of water corresponding to 100% of his body weight loss induced by dehydration. (H1 and E1) or levels of fluid deficit were ma intained (H0, E0). In the E0, H0 and control conditions, the subject drank a solution containing the same quantity of glucose diluted in 100 ml of wat er. Psychological tests were administered 30 min after the dehydration phas e and 2 h after fluid ingestion. Both dehydration conditions impaired cogni tive abilities (i.e. perceptive discrimination, short-term memory), as well as subjective estimates of fatigue, without any relevant differences betwe en the methods. By 3.5 h after fluid deficit, dehydration (H0 and E0) no lo nger had any adverse effect, although the subjects felt increasingly tired. Thus, there was no beneficial effect of fluid ingestion (HI and El) on the cognitive variables. However, long-term memory retrieval was impaired in b oth control and dehydration situations, whereas there was no decrement in p erformance in the fluid ingestion condition (H1, E1). (C) 2001 Elsevier Sci ence B.V. All rights reserved.