About this trial

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.

Eligibility criteria

This trial accepts healthy volunteers

Qualifiers

Individuals who…

…are free-living, who fully understand and agree to the objectives of the study, who gave, signed and dated informed consent, which includes compliance with the requirements and restrictions listed in the informed consent form and in this protocol.

…are 'healthy' men and current combined oral contraceptive (COC)-using women (having taken the COC for at least 3 months and should they be eligible and willing to participate, are happy to continue taking the same COC during the duration of their participation).

…are aged 18-35 years

Disqualifiers

Individuals who…

…are vulnerable, as defined by individuals whose willingness to volunteer in the study may be unduly influenced by the expectation, whether justified or not, of benefits associated with participation, or of a retaliatory response from senior members of a hierarchy in case of refusal to participate (for example, if members of a group with a hierarchical structure linked to the investigator or to the sponsor, subordinate laboratory personnel, and employees of the investigator or sponsor.

…are not able to answer questionnaires by writing whatever the reason.

…have a loss of personal liberty, by administrative or judicial decision.

Trial design

Design model

Parallel

Treatments tested in this trial

Modifying daily total fluid intake
Behavioral
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.

Treatment groups

192 Participants

are divided into 2 treatment groups

Group A: Verification periodNo intervention 0 interventions

Group B: Intervention periodExperimental treatment 1 intervention

Trial outcomes

Primary outcomes

1

Salivary cortisol reactivity to acute psychosocial stress

Changes in the concentration of salivary free cortisol throughout the psychosocial stress test. Cortisol will be measured in stimulated saliva samples and analysed by ELISA. Delta changes (increase/decrease) in cortisol response will also be calculated.

Time frame

Assessed during the main trial (day 8 of the intervention period). Saliva samples will be taken pre (-30 and -5 minutes) and post (+0, +10, +20, +30, +45 and +60 minutes) stress test.

Secondary outcomes

1

Plasma copeptin

Plasma copeptin will be analysed by ELISA and compared cross-sectionally between intervention conditions.

Time frame

Copeptin will be assessed using a single blood sample taken on the morning of the main trial (day 8 of intervention period).

2

Urine osmolality (UOsm)

The concentration of osmotic solutes present in the urine, measured using a freezing point depression osmometer.

Time frame

Late-afternoon urine samples will be collected on days 6 and 7 of the verification and intervention periods. Spot urine samples will be collected on the morning and afternoon visits of the main trial (day 8 of the intervention period).

3

Urine colour

Urine colour, a common marker used for assessing hydration status, will be assessed using a urine colour chart that has been developed to assess urine concentration in healthy humans.

Time frame

Late-afternoon urine samples will be collected on days 6 and 7 of the verification and intervention periods. Spot urine samples will be collected on the morning and afternoon visits of the main trial (day 8 of the intervention period).

4

Plasma osmolality

A marker of intracellular osmolality, measured using a freezing point depression osmometer. Plasma will be derived from venous blood.

Time frame

A venous blood sample will be taken on the morning of the main trial (day 8 of the intervention period).

Other outcomes

1

State anxiety (STAI-S) response to acute psychosocial stress

State anxiety will be assessed throughout the acute stress test using the state aspect (form Y1) of the State-Trait Anxiety Inventory (STAI-S).

Time frame

Assed during the main trial (day 8 of the intervention period). The STAI-S will be administered pre (-30 and -5 minutes) and post (+0, +10, +20, +30, +45 and +60 minutes) stress test.

2

Subjective stress response to acute psychosocial stress

Subjective stress will be assessed using the Subjective Stress Scale, a 0-9 Likert scale where participants rate how stressed they feel right now (0 = no subjective stress experience, 4 = moderate subjective stress experience, 9 = extreme subjective stress experience).

Time frame

Assessed during the main trial (day 8 of the intervention period). The Subjective Stress Scale will be administered pre (-30 and -5 minutes) and post (+0, +10, +20, +30, +45 and +60 minutes) post stress test.

3

Trait anxiety (STAI-T) profiling

Trait anxiety will be measured using the trait aspect (form Y2) of the State-Trait Anxiety Inventory (STAI-T). The STAI-T will be used as a part of participant profiling and demographic assessment.

Time frame

The STAI-T will be administered once, immediately after enrolling.

4

Sleep quality (PSQI) profiling

The Pittsburgh Sleep Quality Index (PSQI) will be used to profile participants' sleep quality in the month prior to the study.

Time frame

The PSQI will be administered once, immediately after enrolling.

The Influence of Fluid Intake on Mental Performance

About this trial

Eligibility criteria

Qualifiers

Disqualifiers

Trial design

Treatments tested in this trial

Treatment groups

Trial outcomes

Primary outcomes

Secondary outcomes

Other outcomes

Sponsors and contacts