Effects of winter sea bathing on psychoneuroendocrinoimmunological parameters.
Level 3 - non-randomized controlled study
Non-randomized cross-sectional study comparing winter sea bathers to non-bather controls.
PubMed 32224255 · doi:10.1016/j.explore.2020.02.004
What was done
A cross-sectional study compared 107 winter sea bathers with 121 non-bather controls (total n = 228, ages 19–88 years). Participants completed questionnaires assessing sociodemographics, self-perceived mental and physical health, Big Five personality traits, and retrospective frequency, duration, and intensity of upper respiratory tract infections (URTIs) over the previous year. A subgroup of 17 bathers and 15 controls (mean age 67 years) underwent an ear-nose-throat (ENT) examination and provided saliva samples to measure cortisol, sIgA, IL-1β, and IL-6.
What was found
Winter sea bathing was associated with lower self-reported stress and higher wellbeing. In the subsample, ENT examinations found no signs of URTIs in bathers, who demonstrated significantly higher levels of salivary sIgA than controls. No significant differences were observed between groups for salivary cortisol or IL-1β. The abstract reports no exact numerical values, effect sizes, p-values, or IL-6 results.
Why it matters
This study provides preliminary observational evidence that regular cold-water swimming is associated with higher mucosal immunity markers and better self-reported psychological wellbeing, even in older adults.
Limits
The cross-sectional design cannot establish causality, making healthy-user self-selection a major confounder. URTI incidence was self-reported retrospectively over a full year, introducing recall bias. The physiological and biomarker analyses were restricted to a very small subset (n = 32), and numerical data were omitted in the abstract.