The evidence
What the studies actually say —
including where they are thin.
Moderate evidence for reduced inflammation and short-term mood lift; weaker evidence for the bigger claims. We report study type, sample size, and an effect size we don't inflate.
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Cold Exposure and Sleep Quality
Sleep · 2021Evening cold exposure may shorten sleep onset in some people.
A small pilot found shorter reported sleep onset after late-afternoon immersion, with no change in total sleep time. The effect was inconsistent across participants and the sample was tiny.
Pilot crossover study 21 participants Effect strength: Weak