Effects of cold-water immersion on health and wellbeing: A systematic review and meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized trials
PubMed 39879231 · doi:10.1371/journal.pone.0317615
What was done
Systematic review and random-effects meta-analysis of randomized trials evaluating acute or long-term cold-water immersion (CWI: cold shower, ice bath, or plunge with water temperature <=15°C for >=30 seconds) in healthy adults aged 18 and older. Outcomes assessed included inflammation, stress, immunity, sleep, mood, fatigue, and quality of life. Eleven randomized studies comprising 3,177 participants (mean PEDro score 6.4; 7 moderate quality, 4 high quality) met inclusion criteria, with interventions delivered via baths (n = 10) or showers (n = 1) across temperatures of 7°C to 15°C and durations of 30 seconds to 2 hours.
What was found
Inflammation significantly increased immediately post-CWI (SMD 1.03, 95% CI 0.37 to 1.68, p < 0.01) and at 1 hour post-CWI (SMD 1.26, 95% CI 0.59 to 1.94, p < 0.01). Stress showed a significant reduction at 12 hours post-CWI (SMD -1.00, 95% CI -1.40 to -0.61, p < 0.01), but no significant differences immediately (SMD -0.09, 95% CI -0.45 to 0.63), at 1 hour (SMD -0.29, 95% CI -0.66 to 0.08), at 24 hours (SMD -0.06, 95% CI -0.50 to 0.38), or at 48 hours (SMD 0.09, 95% CI -0.28 to 0.46; all p > 0.05). Immune function showed no significant acute changes immediately (SMD -0.16, 95% CI -0.82 to 0.51, p > 0.05) or at 1 hour (SMD -0.18, 95% CI -1.09 to 0.74, p > 0.05). Narrative synthesis reported a 29% reduction in sickness absence among cold shower users, as well as improvements in sleep quality and quality of life, but no effect on mood.
Why it matters
This review clarifies the physiological time course of cold-water immersion, showing an acute inflammatory spike followed by delayed stress reduction at 12 hours, while finding no pooled evidence for immediate immune boosts or mood alterations.
Limits
The findings are limited by a small total number of RCTs (11 studies), majority moderate study quality (7 of 11), small individual study sample sizes, and lack of diversity in participant populations. Intervention protocols varied substantially in exposure duration (30 seconds to 2 hours), water temperature (7°C to 15°C), and modality (10 baths vs. 1 shower), and several outcomes like sickness absence, sleep, and quality of life could only be narratively summarized.
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