Even mild dehydration can make stress worse, according to surprising new research.

A study published in the Journal of Applied Psychology found that drinking less than 1.5 liters of water daily significantly raised cortisol levels — the body’s main stress hormone — during stressful situations.

The Study

For the study, researchers divided healthy young adults into two groups. The low-fluid group drank less than 1.5 liters (approximately 6 eight-ounce glasses) a day. The men in the high-fluid group drank more than 2.5 liters (approximately 10.5 eight-ounce glasses) and women drank more than 2 liters (about 8 eight-ounce glasses) a day.

After one week, both groups underwent a lab stress test involving public speaking and math challenges. The low-fluid group had a much stronger cortisol surge.

Why It Matters

Chronic high cortisol can increase the risk of heart disease, diabetes, and kidney problems. Interestingly, the dehydrated participants didn’t report feeling thirsty — but their darker urine showed otherwise.

When the brain senses dehydration, it releases vasopressin, a hormone that conserves water. But vasopressin also boosts cortisol, heightening the stress response.

Beyond Hydration

While drinking enough water won’t eliminate stress on its own, it can be an important part of overall stress management along with:

• Quality sleep
• Good nutrition
• Regular exercise
• Mindfulness and meditation

The authors caution that long-term studies are needed to confirm whether staying well-hydrated can reduce stress-related health risks over decades.