Overview

• Liverpool John Moores University researchers reported the findings on August 22, 2025 in the Journal of Applied Physiology.
• Adults consuming under 1.5 liters daily showed more than a 50% greater salivary cortisol response to a lab stress task than peers meeting intake recommendations.
• Hydration was monitored for a week using urine and blood markers, with the low-intake group displaying darker, more concentrated urine despite similar self-reported thirst.
• Subjective anxiety and heart-rate increases were similar across groups, indicating the heightened response was specific to cortisol.
• Authors point to EFSA and UK Eatwell fluid targets as practical guidance and emphasize that the observed links are associative and need confirmation in larger, longer trials.