Why do we already experience a drop in performance... even before we feel thirsty?

We’ve all learned to listen to our thirst. However, physiology shows us that thirst isn’t the first sign of dehydration. As the temperature rises, our bodies immediately activate their thermoregulatory mechanisms. We lose water through sweating, the heart works harder to maintain blood flow, and the brain must already adapt to this new balance. A decline in performance can therefore begin… even before the sensation of thirst sets in. This is precisely what recent scientific literature shows. The right strategy, therefore, is not to drink when you’re thirsty, but to stay hydrated before that signal appears—especially during prolonged exposure to heat. Whether you’re an athlete, a leader, a member of the military, a healthcare professional, or simply facing the intense heat of summer, understanding this mechanism helps you better preserve your decision-making abilities, alertness, and performance. This week, the “Monday Column – Human Performance” explores the link between heat, hydration, and performance, based on the review by Donnan et al. (2023). “In physiology, waiting until you’re thirsty often means acting… too late.”