Drinking water has been demonstrated to improve adult cognitive functions in a variety of situations. The effect on children is far less studied, even though they tend to be at a greater risk of becoming dehydrated. Pediatric research has detected benefits in attention and working memory as a result of drinking water, but the relationship has not been examined under multiple circumstances.
A study published in the academic journal Appetite expands upon these findings by taking the hydration status of children into account, and revealing that the cognitive benefits of drinking water can be diminished by existing dehydration.
The experiment, performed by Clinton S. Perry III and colleagues, included 52 children between the ages of 9 and 12 years old. Each child took part in two separate trials in which they started their day by consuming a standard breakfast and 200ml of water. In one session no water was given following the initial meal (the control condition), while the other required them to drink an additional 750 ml of water over a 2-hour period (the treatment condition). In both trials, hydration was measured at several points using urine sample analysis, and a trio of cognitive tests were administered after breakfast as well as later in the day.
All participants became less dehydrated as each day progressed, and the change was significantly larger on the day extra water was consumed. Cognitive benefits were only visible on the treatment day, which corresponds with extant research. Results from this day were examined further by splitting the children into two groups: low hydration change and high hydration change (based on comparisons to the median score). Small changes are theorized to represent existing dehydration, as the extra water is used up by the body instead of being excreted. As expected, children who displayed small changes had better cognitive performances later in the treatment day but not the control day, while those exhibiting more change had their best results following extra water consumption.
The results of this study suggest that not all children will benefit cognitively from drinking water. Existing dehydration may prevent such gains by necessitating that the water be used elsewhere in the body, instead of where it would benefit cognition the most (presumably within the brain). The evidence also hints that water intake may actually impair cognition in children who are significantly dehydrated, possibly by initiating restorative processes that divert even more resources from the brain. These findings should lead to many additional explorations that address such possibilities, leading to a better understanding of how dehydration affects cognition in children.