Key Points:
- Dehydration raises stress hormones.
- Low hydration spikes cortisol even without thirst.
- Drinking enough water helps manage stress.
LIVERPOOL, England—Failing to drink enough water could make people more vulnerable to dehydration and stress, as well as related health problems, researchers at Liverpool John Moores University (LJMU) reported in a new study.
The research, published in the Journal of Applied Physiology, found that individuals who consumed less than 1.5 liters of fluid per day showed a stress hormone response more than 50% higher than those who met recommended water intake guidelines. Elevated cortisol, the body’s primary stress hormone, is linked to long-term risks including heart disease, diabetes, and depression.
Study details and findings
The study divided healthy young adults into two groups: those in the lowest 25% of daily fluid intake, averaging under 1.5 liters per day, and those in the highest 25%, meeting recommended levels of 2 liters for women and 2.5 liters for men. Participants were monitored for hydration status through blood and urine samples over a one-week period.
Both groups then took part in the Trier Social Stress Test, a standard procedure that simulates real-world stress through tasks such as a mock job interview and mental arithmetic.
Researchers found that both groups reported similar anxiety levels and increases in heart rate during the test. However, only the low-fluid group showed a significant spike in cortisol levels. Despite this, participants in the low-fluid group did not report feeling thirstier, though their urine samples were darker and more concentrated, signaling poor hydration.
“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,” said study lead Professor Neil Walsh of LJMU’s School of Sport and Exercise Sciences. “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.” This is especially important for managing dehydration and stress.
Biological mechanisms behind dehydration and stress
The team explained that dehydration triggers the release of vasopressin, a hormone that helps conserve water in the body by acting on the kidneys. While vasopressin helps maintain blood volume and electrolyte balance, it also interacts with the brain’s stress-response center, the hypothalamus, increasing cortisol release. This dual effect highlights how dehydration and stress are connected biologically.
This dual effect means the body conserves water but at the cost of higher stress hormone levels, which, if sustained, can contribute to chronic health risks.
“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,” said Dr. Daniel Kashi, a physiologist and member of the LJMU research team. “An important observation was that poor hydration was associated with greater cortisol reactivity to the stress test. Exaggerated cortisol reactivity to stress has been associated with poor long-term health.”
Public health implications
The researchers emphasized that their findings support existing hydration guidelines: about 2 liters of fluid daily for women and 2.5 liters for men. While more long-term studies are needed, the results suggest that maintaining proper hydration could be a simple, low-cost way to help the body manage stress more effectively.
“Being hydrated may help your body manage stress more effectively,” Dr. Kashi said. “A practical way to check your hydration status is to monitor your urine color — light yellow typically indicates good hydration.”
The study was funded by Danone Research and Innovation. Researchers say the next step is to investigate whether improving hydration in chronically under-hydrated individuals can reduce their cortisol responses and improve long-term health outcomes.
For now, the message is straightforward: keeping a bottle of water nearby may do more than quench thirst. It could play a role in protecting mental and physical health against the strains of daily dehydration and stress.
