While it has long been known that dehydration affects cognition and mood in adults, few studies have examined the impact of hydration on cognitive health in children. This gap in knowledge is concerning since children may be at increased risk for insufficient fluid intake as they often depend on adults for regular access to water. Furthermore, children have a higher daily water requirement relative to body mass compared to adults. 

According to a new study published in The Journal of Nutrition, modulating water intake not only influences hydration among preadolescent children but can also influence certain aspects of cognitive performance. 

To investigate the effects of water intake on urinary markers of hydration and cognitive control, children between 9 and 11 years of age participated in a study in which they maintained their desired water intake or consumed high or low amounts of water for 4 d.  Performance on cognitive tasks requiring inhibition, working memory and cognitive flexibility were used to assess cognitive control. The team of researchers lead by Naiman Khan (University of Illinois) hypothesized that insufficient hydration would be inversely associated with cognitive performance and that improving hydration would have a positive effect on participants’ cognitive performance.

Results showed that children with higher baseline hydration performed better on a task-switching activity designed to measure cognitive flexibility. Statistical analyses comparing the intervention effects on hydration indices revealed that all urinary biomarkers differed between interventions: after drinking more water for several days, the children’s hydration improved – as was expected.

However, many of the children had the same or only slightly different values in urinary markers of hydration in the low-water condition as they did at their baseline. This indicates that they may be underhydrated in their everyday activities. In addition to improved urinary markers of hydration, high water intake was selectively related to benefits in working memory and cognitive flexibility.  Participants exhibited 34% lower working memory cost relative to the low water intervention. No difference was observed between conditions on tests designed to measure attention and inhibition. Collectively, these findings support the benefits from 4-d water-based hydration for selective aspects of cognitive function and provide insights into the importance of habitual hydration. 

These results are particularly important for children as greater performance on cognitive control tasks is predictive of academic achievement. A corresponding editorial by David Benton and Hayley Young suggests that a better understanding of the implications of differences in hydration throughout the day is important to ensure an appropriate patterns of fluid intake in children.

Reference Khan NA, Westfall DR, Jones AR, Sinn MA, Bottin JH, Perrier ET, Hillman CH. A 4-d water intake intervention increases hydration and cognitive flexibility among preadolescent children. The Journal of Nutrition , Volume 149, Issue 12, December 2019, Pages 2081–2082, https://doi.org/10.1093/jn/nxz206.

Benton D, Young HA.  Water: The Cinderella Nutrient. The Journal of Nutrition , Volume 149, Issue 12, December 2019, Pages 2255–2264, https://doi.org/10.1093/jn/nxz226.

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