A study  published in the Journal of Applied Physiology found that people who drank less than about 1.5 liters a day showed significantly higher cortisol levels, the body’s main stress hormone, when faced with a stressful situation.

 Their cortisol response was over 50% higher than people who regularly met recommended daily fluid intake. In other words: how much you drink may influence how intensely your body reacts to stress.

One surprisingly simple marker predicted this: morning urine color. Participants with darker urine (color chart score of 4 or higher) were not only consistently more dehydrated but also had stronger cortisol spikes under stress.

Researchers from Liverpool John Moores University grouped healthy adults ages 18 to 35 into two categories according to national hydration data: 

Both groups maintained these habits for a week while logging everything they drank. Afterward, they completed a validated laboratory stress test designed to mimic real-life pressure: a mock job interview followed by difficult mental math. 

To measure cortisol, researchers collected saliva samples before the test, immediately after, and several times over the next hour. Participants also provided blood and urine samples to assess hydration.

 Although both groups felt equally anxious and showed similar heart rate increases, the low-fluid group had significantly higher cortisol at baseline and mounted a much stronger cortisol response to the stress test, even though the psychological and physical experience of stress felt the same. 

It’s important to note that this study was small and cross-sectional. It identifies associations, not cause-and-effect. Still, the patterns were strong and biologically plausible.

New research shows that people who feel overwhelmed or unusually reactive often share one simple, silent factor—and it has nothing to do with personality or anxiety.

It comes down to a hydration imbalance that can cause your body to release over 50% more cortisol during stress. In other words, even mild dehydration can push your stress response into overdrive without you noticing.

The good news?
A leading physiologist reveals a quick, practical way to fix this trigger and help your body stay calmer and more resilient—starting today.

>> WATCH NOW: The Simple Hydration Habit That Helps You Stay Calm Under Stress

When you’re dehydrated—even mildly—your brain releases vasopressin, a hormone that helps your body conserve water.

Vasopressin:

 In the study, people who drank the least had higher vasopressin levels. Elevated vasopressin essentially keeps the stress system on a hair-trigger. So when a real stressor hits, the body pumps out more cortisol than it otherwise would.

Cortisol is helpful in the short term. It sharpens your focus and helps you rise to immediate challenges. But if it stays high too often or for too long, it can contribute to “wear and tear” on the body: higher inflammation, disrupted sleep, faster fatigue, blood sugar issues, and increased vulnerability to illness.

Chronic dehydration adds to the problem. Dehydration is linked to constipation, brain fog, urinary tract infections, kidney stones, kidney failure risk, and even metabolic and cardiovascular disease.

Feeling stressed is normal—and often has many contributors. But hydration is one of the simplest to address. If you find yourself snapping at people, feeling unusually wired, or more reactive than usual, it might help to start with something easy: drink a few glasses of water.