Can water improve executive functions via changes in heart rate variability?

Introduction Drinking water has been shown to improve performance on executive functions (EF). The underlying mechanisms have been recently debated in a review, which argues, besides other factor, for physiological changes, as water has been found to increase heart rate variability (HRV; Masento et al., 2014). As EF are linked to HRV (neurovisceral integration model; Thayer et al., 2009), this study aims to examining the effects of oral water intake on EF and non-EF via HRV changes. Method In a within-subject design, 43 volunteers (28 females; Mage = 22.3±2) participated in two conditions (water vs. no-water). In the water condition, they were tricked into drinking 500 ml of water (i.e., cover story), whereas they did not drink in the no-water condition. Watching a 25 min video followed this. Then, the EF task (i.e., digit span task, DS) and the non-EF task (i.e., simple reaction time task, SRT) were per-formed. HRV was measured at baseline (BL), during the movie, during the tasks (DS, SRT), and at recovery (REC) in intervals of 5 min. Results HRV was significantly higher in the water condition in comparison to the no-water condition (p = .002, η2 = 0.23; see Figure 1). Non-EF and EF tasks showed no significant main effect but a significant interaction effect (condition*order) was found for DS (p < .001, η2 = 0.3), presenting a learning effect. Discussion Drinking water increases HRV and potentially has a positive impact on performance on EF, which would be in line with the neurovisceral integration model (Thayer et al., 2009). Future research should account for the found order effect due to learning by using correlated but not identical tasks. Literatur Masento, N. A., Golightly, M. Field, D. T., Butler, L. T., & van Reekum, C. M. (2014). Effects of hyd-ration status on cognitive performance and mood. British Journal of Nutrition, 111, 184-1852. Thayer, J. F., Hansen, A. L., Saus-Rose, E., & Johnsen, B. H. (2009). Heart rate variability, prefrontal neural function, and cognitive performance: the neurovisceral integration perspective on self-regulation, adaptation, and health. Annals of Behavioral Medicine, 37, 141-153.