Overview

• Adults drinking under 1.5 litres per day showed more than a 50% higher cortisol rise during a validated lab stress test than better-hydrated peers.
• The Liverpool John Moores University study screened 62 healthy adults and enrolled 32 who maintained their usual intake for seven days before testing.
• Self-reported nervousness and heart-rate increases were similar between groups, yet cortisol spiked markedly more in low-intake participants.
• Urine measures indicated poorer hydration in the low-intake group even though they did not report greater thirst, suggesting thirst can be an unreliable cue.
• Researchers propose a vasopressin-linked mechanism for the amplified response, and UK NHS guidance recommends six to eight drinks a day.