The use of moderated mediated analysis to study the influence of hypo-hydration on working memory.

INTRODUCTION: To date, dehydration has been typically reported to infl uence psychological parameters when there has been at least a 2% loss of body mass, although there has been little examination of those going about their everyday lives, those who have lost less than 1% of body mass. In such situations factors such as the initial hydration status and individual differences in the response to a reduced fl uid intake are likely to be infl uential. Yet to study the complexity added by such additional variables novel methods of statistical analysis are required.

OBJECTIVES: The present study describes the use of moderated mediation, an approach that asks various questions: fi rstly, is drinking infl uential?; secondly, does a mediator (e.g.,thirst) sit between an independent and dependent variable?; and thirdly, does an effect only occur under certain conditions such as initial osmolality?

METHOD: In the study, 118 subjects were exposed to 30 °C for four hours during which they half drank 300 ml water. The serial sevens test of working memory was performed before and at the end of the procedure.

RESULTS: A 0.6% loss of body mass reduced the effi ciency of working memory. Those who consumed water had better working memory; working memory was worse in participants who lost more body mass or became thirstier, but only in those with higher levels of baseline osmolality.

CONCLUSIONS: Small variations in hydration status infl uenced cognitive functioning although there were individual differences in the response. The parameters that influence an adverse response to hypo-hydration need to be established to allow giving appropriate advice.