The Influence of Fluid Intake on Mental Performance

Over half of the adult population in Europe, Asia and Latin America fail to meet adequate water intake guidelines as advised by the European Food Safety Authority (EFSA; 2.5 and 2 litres/day for men and women, respectively coming from both food and drinks). Increasing epidemiological evidence suggests that chronic low fluid intake may be associated with an increased risk of cardiovascular, metabolic, and renal diseases. The association between chronic low fluid intake and increased morbidity risk may be underpinned by elevations in key water-regulating hormones, such as arginine vasopressin (AVP) and its surrogate copeptin, which influence glucose regulation and renal function. For example, AVP stimulates the hypothalamic-pituitary adrenal (HPA) axis to release the stress hormone cortisol with potentially far-reaching effects on metabolism, immunity and inflammation. Prospective cohort studies have demonstrated that exaggerated cortisol responses to acute stress are associated with poor health outcomes. A recent cross-sectional study (NCT05491122) from our group found that individuals with a low habitual fluid intake experienced greater cortisol reactivity to acute stress than those with a high habitual intake. The findings of this study may provide a potential explanation for why poor hydration and low fluid intake have negative effects on long-term health. We now aim to explore whether altering fluid intake influences cortisol reactivity to acute stress.