Water consumption, not expectancies about water consumption, affects cognitive performance in adults

Abstract

Research has shown that water supplementation positively affects cognitive performance in children and adults. The present study considered whether this could be a result of expectancies that individuals have about the effects of water on cognition. Forty seven participants were recruited and told the study was examining the effects of repeated testing on cognitive performance. They were assigned either to a condition in which positive expectancies about the effects of drinking water were induced, or a control condition in which no expectancies were induced. Within these groups, approximately half were given a drink of water, while the remainder were not. Performance on a thirst scale, letter cancellation, digit span forwards and backwards and a simple reaction time task was assessed at baseline (before the drink) and 20 minutes and 40 minutes after water consumption. Effects of water, but not expectancy, were found on subjective thirst ratings and letter cancellation task performance, but not on digit span or reaction time. This suggests that water consumption effects on letter cancellation are due to the physiological effects of water, rather than expectancies about the effects of drinking water.

Habitual total water intake and dimensions of mood in healthy young women

“…Two investigations to our knowledge have examined acute water boluses that did not result in changes in mood parameters (Edmonds, Crombie, Ballieux, Gardner, & Dawkins, 2013;. Even fewer studies have examined the relationship between habitual total water intake across days (TWI; total moisture in solid foods plus water and beverages) and mood; the simple act of changing drinking behavior might contribute to improved mood state.…”

Water consumption as a source of error in the measurement of heart rate variability

“…While the effect of water on cognition is equivocal, it has been observed to improve performance on tasks which involve psychomotor speed or visual attention both in children (Benton & Burgess 2009) and adults (Edmonds et al 2013). This body of work frames drinking in terms of the presence/absence of a degree of dehydration (rather than the presence/absence of drinking water), and has so far been investigated independently of similar visual attention tasks that affect LF HRV.…”

“…The assumption in much of the literature relating hydration to task performance is that water is correcting sub-optimal hydration or dehydration, without an immediate concern for the mechanism involved (Edmonds & Burford 2009;Edmonds et al 2013). However, the potential positive effects of drinking water (i.e., elevated hydration from a normal baseline) are not necessarily mediated by the same mechanism as the removal of potential negative effects due to dehydration; in many studies on hydration, participants are exercised or water restricted (from 1% to 4% of bodyweight; see Secher & Ritz 2012 for review).…”

The effect of carbohydrate mouth rinse on a 30-minute arm cranking performance

“…The task required participants to cross off as many of the letter 'U' as they could from a matrix of letters in 30 seconds. This test has been shown to be a valid and reliable measure of visual attention (cognitive function) (Edmonds and Burford, 2009;Edmonds et al, 2013;Edmonds and Jeffes, 2009). The participants were fitted with a heart rate monitor (Polar FT1) and their resting heart rate was recorded.…”

“…On arrival, body mass, blood pressure (BP), and blood lactate (BL) were recorded and a letter cancellation task was performed (Edmonds et al, 2013). The task required participants to cross off as many of the letter 'U' as they could from a matrix of letters in 30 seconds.…”