A recent meta-analysis published by Medicine and Science in Sports and Exercise showed that mild dehydration can affect a wide range of cognitive functions including: motor coordination, mood and reaction time. The meta-analysis included 33 studies with 413 subjects and dehydration ranging from 1-6% of body mass loss. Outcome variables (reaction, coordination) and methods of inducing dehydrating varied. Results showed that as dehydration occurs, loss of attention, executive function and motor coordination are more likely to degrade while tasks requiring less attention such as information processing or memory were not. This is the first study which identified that dehydration can affect high-order cognitive processing (involving attention) more than low-order cognitive processing (simple reaction time). Future research should focus on mechanistic explanations and if dehydration effects vary with physical activity levels (sedentary vs. athlete).
Study Strengths: This is the first meta-analysis to systematically suggest that dehydration can significantly affect cognitive performance. The authors controlled for variation of several study design factors that can contribute to heterogeneity of results which strengthened this study.
Study Limitations: The analysis showed significant results on dehydration impairing cognitive performance, however, due to the nature of this study, mechanistic explanations cannot be made, and this should be addressed in future research. The authors reported that four studies did not report non-significant findings. Additionally, some of the studies may differ in quality as far as methods, control and convenience sampling. The authors acknowledge that it’s unclear how these variables may have affected the results of this study; therefore, results may change in the future.
What does this mean for your practice? Use this article as a talking point with parents of young children to address the importance of their child drinking enough fluids, especially if they are active or during the hot summer months. The Academy of Nutrition and Dietetics states that as a general rule, children should drink at least 6 to 8 cups of fluids/day along with the recommended servings of fruits and vegetables. Remember that fluid requirements differ greatly depending on age, sex, weight and physical activity level. In hot weather, children need extra water, especially before and during physical activity. This article implies that even mild dehydration may affect things that parents of children may find important such as test scores or athletic performance; however, more research is needed to confirm these findings.
Original article: Wittbrodt, M. T., & Millard-Stafford, M. (2018). Dehydration Impairs Cognitive Performance: A Meta-analysis. Medicine and science in sports and exercise.