RecruitingNAINTERVENTIONAL

The Influence of Fluid Intake on Mental Performance

Many people in Europe and other parts of the world don't drink as much water as experts recommend. Research suggests that not drinking enough over time could be linked to various health issues, including heart and kidney problems. This might be because of how your body manages water and stress hormones. We've previously found that people who drink less water tend to react more strongly to stress. This study aims to find out if we can change this stress response by simply encouraging people to drink more or less fluid. We want to understand if adjusting your daily fluid intake can help improve how your body deals with stress and, in turn, potentially benefit your overall health.

At a glance

Status

Recruiting

Phase

Sponsor

Liverpool John Moores University

Enrolment target

192

Start

22 Jun 2026

Estimated completion

01 Dec 2027

Hydration Status Psychosocial Stress Fluid Intake

What is this study about?

This study is looking into how much fluid we drink and how it affects our minds and bodies. You might be surprised to learn that many adults don't drink the recommended amount of water each day, which is about 2.5 litres for men and 2 litres for women, including fluids from food. There's a growing understanding that not drinking enough over a long time might be linked to health problems like heart disease, diabetes, and kidney issues.

One way this could happen is through hormones in our body that control water balance. These hormones can also affect our stress response. For example, a hormone called AVP can trigger the release of cortisol, known as the 'stress hormone'. High levels of cortisol over time can impact many things, including our metabolism, immune system, and how our body deals with inflammation. Previous studies have shown that having a strong cortisol reaction to stress might not be good for our health in the long run.

Our research team recently found that people who usually drink less fluid tended to have a stronger stress response compared to those who drink more. This new study is designed to follow up on those findings. We want to see if making changes to how much fluid people drink each day can actually change how their body reacts to stress. By understanding this, we hope to find out if improving your hydration could be a simple way to help your body manage stress better and support your long-term health.

Key takeaways

This study explores the link between daily fluid intake and your body's stress response.
Many adults don't drink recommended fluid levels, which might impact long-term health.
We previously found lower fluid intake linked to a stronger stress reaction.
The study aims to see if changing fluid intake can improve how you handle stress.
Participation involves adjusting fluid intake, tracking with an app, and providing samples.

Who may be eligible?

To take part in this study, we're looking for healthy men and women who are currently using a specific type of contraception (combined oral contraceptive pill) and have been for at least three months. You need to be between 18 and 35 years old. It's also important that you don't do more than 5 hours of strong exercise each week.

We are particularly interested in people who either drink quite a low amount of fluid each day (less than about 1.6 litres for men, or 1.5 litres for women) or quite a high amount (more than about 2.9 litres for men, or 2.5 litres for women). We'll check this by asking you to record what you drink for 7 days. You'll also need a fridge at home to store urine samples and own a smartphone (Apple or Android) to use a special app. Your body weight should be within a healthy range (BMI below 30).

There are also some reasons why you might not be able to join, such as if you are considered a 'vulnerable' person where agreeing to take part might feel pressured. We want to make sure everyone who joins does so freely and willingly.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

Are you a healthy man or a woman using the combined oral contraceptive pill?
Are you between 18 and 35 years old?
Do you do less than 5 hours of strong exercise per week?
Do you either drink very little fluid (e.g., less than 1.6 litres for men or 1.5 litres for women) OR quite a lot (e.g., more than 2.9 litres for men or 2.5 litres for women) each day?
Do you have a fridge at home and a smartphone (Apple or Android)?
Is your BMI (body weight to height ratio) below 30?

Answer every question to see your result.

What does participation involve?

If you join this study, we'll ask you to come in for some visits to our research centre. We'll also ask you to adjust your daily fluid intake for a period, either increasing or decreasing it, depending on which group you're in. This will involve carefully tracking what you drink using a special water bottle that links to an app on your smartphone, and keeping records of your fluid intake. We'll also collect urine and blood samples to check your hydration levels and stress hormones.

During your time in the study, we might ask you to do some tasks that can create a mild amount of stress, so we can measure your body's response. You will need to store urine samples in your home fridge before bringing them to us. The total length of time you'll be involved in the study will be explained in full, including any follow-up appointments.

Potential risks and benefits

There are no direct benefits to you from taking part in this study, but the information we gather could help us understand how hydration affects stress and overall health for many people in the future. We don't expect any serious risks. You might feel a little discomfort from blood tests, and adjusting your fluid intake might feel unusual at first, but we will provide clear guidance and support. You are completely free to withdraw from the study at any time, for any reason, without it affecting your medical care.

Locations (1)

Liverpool John Moores University
Verified postcode
Liverpool, United Kingdom· Recruiting

Common questions

What do you mean by 'fluid intake'?

Fluid intake includes all liquids you drink, such as water, tea, coffee, juice, and also the water content in your food.

Will I have to drink a specific type of fluid?

You will be asked to adjust your overall daily fluid intake, but we will give you guidance on what types of fluids are suitable for the study.

What kind of 'stress' will I be exposed to?

You might be asked to do some mild tasks that cause a small amount of mental stress, such as public speaking or mental arithmetic, so we can measure your body's reaction.

How often will I need to visit the study centre?

The number of visits will be explained in detail if you are invited to participate, but it will involve several visits over the course of the study.

Is my personal information kept private?

Yes, all your personal information and study results will be kept strictly confidential and anonymous in our research.

How to find out more

William J Searle, PhD

w.j.searle@ljmu.ac.uk 01519041031 Official trial record

Always speak to your GP or specialist before deciding to take part in a study.