The study indicates that those who consume less than the recommended daily fluid intake exhibit a stronger stress hormone response, potentially elevating the risk of heart disease, diabetes, and depression.

The findings, recently published in the Journal of Applied Physiology, revealed that participants who drank fewer than 1.5 liters of fluid daily experienced a cortisol response to stress that was more than 50% higher compared to those who met the recommended daily water intake.

Professor Neil Walsh, the study’s lead physiologist at LJMU’s School of Sport and Exercise Sciences, stated: “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,” Professor Neil Walsh added.

Dehydration and Long-Term Health Risks

Professor Neil Walsh and his team, with funding from Danone R&I, divided healthy young adults into two equal groups based on their daily fluid intake. The ‘low fluid’ group consumed less than 1.5 liters of fluid per day,while the ‘high fluid’ group met the daily recommendations of 2 liters for women and 2.5 liters for men. Both groups were carefully matched for factors known to influence stress responses, such as psychological characteristics and sleep patterns.

“If you have a stressful schedule, keeping a bottle of water close could be a good habit.”

Dr Daniel Kashi, physiologist, LJMU

The participants maintained their usual drinking habits for a week, during which researchers monitored hydration levels through blood and urine samples. Subsequently, they underwent the Trier Social Stress Test, a widely used method to simulate real-world stress through a mock job interview and mental arithmetic tasks.

Dr Daniel Kashi, a member of the study team, explained: “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.”

Dr. Daniel Kashi further noted: “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. An significant 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.”

The Science Behind Dehydration’s Harmful Effects

Dehydration’s negative impact stems from the body’s water-regulation system, which is closely linked to the brain’s stress-response center. When the body detects dehydration, whether from insufficient fluid intake or excessive fluid loss, it triggers the release of vasopressin