A new study published in the Journal of Applied Physiology has found that drinking less than 1.5 litres of water daily may significantly amplify the body’s stress response, making everyday pressures harder to manage. Researchers observed that participants with lower fluid intake showed dramatically higher levels of cortisol—the body’s primary stress hormone—when exposed to stressful situations.
The study involved healthy young adults divided into two groups based on their usual hydration habits. After maintaining their fluid intake patterns for a week, participants underwent a stress test involving public speaking and mental arithmetic. While both groups reported similar anxiety levels and heart rate increases, those who drank less water experienced a far more pronounced cortisol surge.
Thirst isn’t always a reliable signal
Surprisingly, the under-hydrated group didn’t report feeling thirstier than their well-hydrated counterparts. However, darker, more concentrated urine revealed their dehydration, suggesting that thirst alone may not be a dependable indicator of fluid needs.
Researchers explained that the body’s water management system plays a key role in this stress amplification. When dehydration is detected, the brain releases vasopressin—a hormone that conserves water by instructing the kidneys to retain fluid. But vasopressin also interacts with the brain’s stress-response system, potentially heightening cortisol release during challenging moments.
A simple fix for a complex problem
This dual effect creates a physiological “double burden”: while vasopressin helps preserve water, it also makes the body more reactive to stress. For individuals juggling work, family, and financial pressures, this heightened reactivity could accumulate into long-term health risks, including heart disease and diabetes.
The findings add hydration to the growing list of lifestyle factors—alongside sleep, nutrition, and exercise—that influence stress resilience. While water isn’t a cure-all, researchers say it’s a simple, universally accessible tool that can support both physical and mental well-being.
Monitoring urine colour—aiming for pale yellow—is a practical way to track hydration.
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