A recent study
examined the influence of hypohydration (a loss of <1% of body mass, changes in urine osmolality, body temperature, and thirst<) on cognition in 101 individuals randomized to either consume or not consume 300 mL of water when subjected to temperatures of 30°C for 4 hours. The participants were blinded and unaware of the purpose of the experiment. While the authors concluded that drinking water benefited cognitive function, the primary weakness of the study is the participants were not randomly allocated to receive the water or not but were assigned alternately by the order they were recruited. It is a concern that they did not use a real randomization method since the timing of the participant’s arrival to the study can be influenced by unknown reasons that could have been related to their hydration status. In addition, the authors did not report the baseline osmolality of the participants in the two groups, which would have been reassuring that they did not have any bias related to their lack of randomization; they only reported the change in urine osmolality after the intervention/no intervention. Lastly, the authors did not control for the hydration status of the participants at the start, which could have influenced their hydration status throughout the experiment. If they had actually randomized the participants to the groups and if they reported their baseline urine osmolality of the groups and if the baseline urine osmolality of the groups were similar, then one could have confidence in their findings. Performing at least 54 statistical tests also helped to increase the chance of finding significant differences by chance alone. More quality studies are needed to confirm water consumption and cognitive function. Dietitians can continue to discuss adequate hydration with their clients achieved through beverages and foods. See: What is the evidence
to support that healthy adults should drink eight 8-oz (250 mL) glasses of
water daily for good health?