The Influence of Fluid Intake on Mental Performance

Summary

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.

Conditions

• Hydration Status
• Psychosocial Stress
• Fluid Intake

Interventions

BEHAVIORAL

Modifying daily total fluid intake

7-day intervention where the intake of drinking water will either be maintained at habitual level, increased (if habitually low) or decreased (if habitually high). The TFI prescriptions during the intervention are derived from the mean TFI of habitually low and habitually high drinkers from a sex, age and country matched population. Specifically, habitually low drinkers will be permitted a TFI of 3.5 L/day for men and 3.3 L/day for women and habitually high drinkers will be permitted a TFI of 1.3 L/day. Participants will be instructed to maintain their usual intake of other beverages i.e., tea/coffee to achieve their target TFI.

Sponsors & Collaborators

• Unilever R&D

  collaborator INDUSTRY

• Liverpool John Moores University

  lead OTHER

Principal Investigators

• Neil P Walsh, PhD · Liverpool John Moores University

Study Design

Allocation

RANDOMIZED

Purpose

BASIC_SCIENCE

Masking

NONE

Model

PARALLEL

Eligibility

Min Age

18 Years

Max Age

35 Years

Sex

ALL

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2026-06-22

Primary Completion

2027-09-01

Completion

2027-12-01

Countries

• United Kingdom

Study Locations