How can a 0.7% loss of body mass influence cognitive functioning? A mechanistic investigation.

Objective: To see if drinking water, when mildly hypohydrated (a loss of 0.7% of body mass), helps to maintain cognitive functioning and mood and to explore underlying mechanisms. Method: 118 (61 male) young adults were exposed to a temperature of 30oC for four hours and either did or did not drink two 150ml glasses of water during that time. On three occasions, once at baseline and once after each drink, they completed cognitive tests and rated their thirst, energy and task difficulty. Changes in body temperature and perspiration were monitored throughout and considered, along with thirst and ratings of difficulty, as potential mediators. Individual differences in habitual water consumption and baseline urine osmolality were also considered.