Not drinking enough water could intensify stress responses. Researchers found that individuals who were under-hydrated had cortisol levels more than 50% higher during stressful situations. Poor hydration didn’t make participants feel thirstier, but it did trigger biological signs of strain. Keeping a water bottle handy can help manage stress and promote overall health.
Drinking too little water could increase our vulnerability to stress-related health issues, according to a new study from scientists at Liverpool John Moores University (LJMU).
People who drink less than the recommended daily fluid intake experience a greater stress hormone response, which is associated with an increased risk of heart disease, diabetes, and depression.
A new study, published recently in the Journal of Applied Physiology, found that individuals who drank less than 1.5 litres of fluid – or seven cups of tea – per day had a cortisol response to stress that was over 50% higher than those who met daily water intake recommendations.
Study lead Professor Neil Walsh, a physiologist in LJMU’s School of Sport and Exercise Sciences, said: “Cortisol is the body’s primary stress hormone and exaggerated cortisol reactivity to stress is associated with an increased risk of heart disease, diabetes and depression.”
“If you know you have a looming deadline or a speech to make, keeping a water bottle close could be a good habit with potential benefits for your long-term health.”
Poor long-term health
With the project funded by Danone R&I, Neil and his team divided healthy young adults into two equally sized groups, representing the lowest and highest 25% for daily fluid intake.
The ‘low fluid’ group consisted of individuals who typically drank less than 1.5 litres of fluid per day (water, hot drinks, etc.).
The ‘high fluid’ group included individuals who regularly met the daily water intake recommendations – 2 litres for women and 2.5 litres for men.
Both groups were matched for key factors known to influence stress responses, including psychological characteristics and sleep patterns.
Participants maintained their usual drinking habits for one week, during which hydration levels were monitored in blood and urine samples.
Then, participants underwent the Trier Social Stress Test, a widely used method for simulating real-world stress through a mock job interview and a mental arithmetic task.
Dr Daniel Kashi, a member of the study team, said: “Both groups felt equally anxious and experienced similar increases in heart rate during the stress test.
However, only the ‘low fluid’ group showed a significant increase in saliva cortisol in response to the stress test.”
He added, “Although the low fluid group did not report being thirstier than the high fluid group, they had darker and more concentrated urine, clear signs of poor hydration.
A notable observation was that poor hydration was associated with increased cortisol reactivity to the stress test. Exaggerated cortisol reactivity to stress has been associated with poor long-term health.”
Why is Dehydration Harmful?
The answer lies in the body’s water-regulation system, which is closely connected to the brain’s stress-response centre.
When the body senses dehydration, whether due to inadequate fluid intake or excessive fluid loss, it triggers the release of a hormone called arginine vasopressin, also known as antidiuretic hormone (ADH) or vasopressin.
Vasopressin acts primarily on the kidneys, promoting water reabsorption to maintain blood volume and electrolyte balance.
This conservation mechanism comes at a cost. Sustained vasopressin release places additional strain on the kidneys, which must work harder to concentrate urine and manage electrolyte balance.
Vasopressin also acts on the brain’s stress-response centre, the hypothalamus, where it can influence the release of cortisol. The dual role of vasopressin helps maintain blood volume and electrolyte balance, while also increasing cortisol levels.
The researchers note that while further long-term studies are necessary, the findings support current water intake recommendations – approximately 2 litres of fluid per day for women and 2.5 litres for men.
Hydration Helps us Manage Stress
“Being hydrated may help your body manage stress more effectively,” added Dr Kashi. A practical way to check your hydration status is to monitor your urine colour — light yellow typically indicates good hydration.
