The Effect of Hypo-Hydration on Mood and Cognition is Influenced by Electrolyte in a Drink and Its Colour: A Randomised Trial

Abstract

Traditionally it has been thought necessary to lose 2% of body mass due to dehydration, before functioning is disrupted, although recently adverse effects have been reported with a loss of 0.5-0.7%. It is, however, unclear whether the response to small decreases in mass reflects dehydration, mechanisms that help to adapt to a loss of bodily fluid, or a placebo effect. Individuals were therefore subject to a temperature of 30°C for three hours, and mood and cognition monitored. To explore the possibility of a placebo response, the consumption of plain or coloured water was compared. To consider changes in hydration status, drinks known to differ in their ability to rehydrate were contrasted. Not drinking was disruptive, although a combination of plain water and electrolyte’s most effectively prevented a decline in functioning, indicating a role for rehydration after a loss of 0.52% body mass. There was, however, also evidence of a placebo response: a combination of plain water and electrolytes was better able to prevent a decline in functioning than coloured plain water and electrolytes. As increased anxiety was a robust response, it was discussed whether the renin–angiotensin–aldosterone system might be part of the mechanism.

Does Hydration Status Influence Executive Function? A Systematic Review

“…Considerable variance in outcomes was also observed in studies including a rehydration or euhydration component ( Figure 5). Of the 27 rehydration studies, 16 studies identified improvements to EF-related tasks as a function of rehydration or euhydration, primarily to working memory or shortterm memory 22,38,42,45,47,[49][50][51]57,59 and attention/inhibitory control. 30,31,32,35,39,42,59 Of the remaining studies, several found dose-dependent effects or effects that required the inclusion of 1 or more covariates or analysis of interaction effects; however, these results are not included as positive findings here.…”