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Inverted "u-shaped" association of cold-water immersion frequency with mental health and upper respiratory tract infection: a cross-sectional study
Cross-sectional internet survey (June 2022; Poland) of 732 self-identified polar plungers versus 501 controls: plungers reported better GHQ-28 mental health and shorter self-reported URTI duration and sick leave; adjusted models suggested an inverted-U relationship with cold-water immersion frequency, with the strongest marginal benefits near about two sessions per week and attenuation or worsening at the highest self-reported frequencies.
Design
- N: 732 cold-water immersion (CWI) practitioners (“polar plunging”) vs 501 controls recruited online
- Setting / timing: Poland; survey fieldwork June 2022
- Outcomes: GHQ-28 total and subscales; self-reported days of upper respiratory tract infection (URTI) in the prior autumn–winter season; self-reported sick leave days attributed to URTI
- Confounders in models: sex, age, multimorbidity (Functional Comorbidity Index), mindfulness (FFMQ-SF), temperament (sensitivity to reward / punishment)
Headline associations (as reported)
- Practitioners vs controls: better global mental-health scores and shorter self-reported URTI and sick-leave durations on average after covariate adjustment (ANCOVA / regression framework in the paper).
- Frequency dose-response: authors describe an inverted-U — gains versus non-practice up to roughly ~2 CWIs per week, with less favorable outcomes at the highest self-reported weekly frequencies in the same adjusted models (see their Table 3 marginal / regression outputs for exact B coefficients and Bonferroni-corrected p-values).
Evidence tier & limits
- Cross-sectional + self-report illness — cannot prove that CWI causes fewer infections or better mood; selection (healthier, more mindful people may start plunging), recall bias, and residual confounding are expected.
- Modality note: respondents describe outdoor plunge-style immersion (seasonal “morsowanie”), not the same stimulus as 30–90 s cold-shower RCTs under Cold exposure therapy (
cold-exposure)—pair with Buijze 2016 and Cain 2025 for multi-modality context rather than merging protocols.
How this database uses the row
Indexed under Cold water immersion (cold-plunge) for dose–frequency hypotheses and under Cold exposure & inflammation (cold-exposure-inflammation) only as self-reported infection-duration association tier—not acute-phase blood CRP/IL-6 panels.
Outcomes
- Depression & Anxiety Composite ScoreGHQ-28 global and subscale scores favored polar plungers vs controls in covariance-adjusted comparisons (η² small; see paper Table 2)—self-report mental-health instrument, not diagnostic interviews.
- Linear regression on CWI frequency: inverted-U pattern for GHQ-28, URTI days, and sick-leave days—strongest marginal improvements near ~2 sessions/week vs reference frequency bands; highest self-reported weekly frequencies associated with worse outcomes than the sweet spot (semi-partial correlations and B coefficients in Table 3).
- URTI duration / sick leave: practitioners reported fewer illness days and fewer sick-leave days than controls on average (Table 1 unadjusted descriptives; adjusted models in later tables)—still association-only.