Deliberately putting oneself into a high-adrenaline state, such as through an ice bath, increases one's ability to buffer stress.

The finding

What the evidence shows

There is a real kernel here. The body clearly gets used to repeated cold, and a small number of studies show that cold habituation can blunt responses to a different stressor such as low oxygen. But the phrase we know for certain goes past what the human data support. A 2025 systematic review and meta-analysis of cold water immersion found no significant effect on stress immediately, at one hour, at 24 hours or at 48 hours, with a single reduction at 12 hours, and the authors describe the evidence base as limited by few trials, small samples and mostly male participants.