Hydration status moderates the effects of drinking water on children's cognitive performance

Changes in hydration status throughout the day may affect cognitive performance with implications for learning success in the classroom. Our study tested the hypothesis that the benefit of drinking water on working memory and attention depends upon children's hydration status and renal response to water intake. Fifty-two children aged 9-12 years old were tested under two experimental conditions. The treatment session (Water session) consisted of a standard breakfast with 200 ml water, a baseline test, consumption of 750 ml of water over a period of two hours and subsequently retested. No water was provided after breakfast during the control session. Changes in hydration were assessed via urine samples. Cognitive testing consisted of digit span, pair cancellation, and delayed match to sample tasks. Children who exhibited smaller decreases in urine osmolality following water intake performed significantly better on the water day compared to the control day on a digit-span task and pair-cancellation task. Children who exhibited larger decreases in urine osmolality following water intake performed better on the control day compared to the water day on the digit-span task and pair-cancellation task. These results suggest that focusing on adequate hydration over time may be key for cognitive enhancement.