As science-et-vie.com reported, the findings stem from a psychology thesis submitted to the Journal of Health Psychology by researcher Lena Glaser.
The investigation tracked 719 healthy participants aged 18 to 65 who were previously unaccustomed to cold water exposure. Despite high initial dropouts during the first two weeks, participants who maintained at least a 70 percent adherence rate drove the observed reduction in reported illness.
- Subjective Reporting vs. Objective Biomarkers: The 26 percent drop in illness relies entirely on participant self-reporting, while physiological health markers did not reach statistical significance.
- Adherence Challenges: The protocol experienced significant attrition early on, meaning only highly motivated individuals completed the full twelve-week duration.
- Environmental and Energy Impact: Lowering water temperatures from 40 °C to 15 °C saves approximately 1.3 kilowatt-hours per 45-liter shower, reducing personal carbon output.
The trials coordinated by Lena Glaser evaluated 719 adults over twelve weeks without enforcing specific dietary or exercise regimens. Adherence proved to be the primary operational hurdle during the trials. Many participants withdrew within the first fortnight of cold immersion before the dropouts stabilized. Among those who completed the protocol, compliance remained high, with 77.3 to 90 percent executing the cold shower routine weekly.
Participants also completed weekly psychological questionnaires alongside the health tracking. The data revealed minor improvements in subjective well-being scores among the cold water group. However, physical health metrics failed to reach statistical significance, indicating that participants felt better mentally without a corresponding measurable physical gain recorded in clinical metrics.
| Study Year | Key Focus | Primary Finding |
|---|---|---|
| 2016 | Dutch clinical trial | Associated cold showers with reduced workplace absences, though reported sick days remained unchanged. |
| 2024 | Immune system signaling | Identified activation of specific immunological pathways in cold water regulars without measuring clinical benefits. |
| 2026 | University of Basel thesis | Linked regular cold showers to a 26 percent reduction in reported sick days among 719 participants. |
Methodological limitations qualify these findings. Because the comparison groups formed organically based on the participants’ actual shower frequency rather than random assignment, researchers cannot definitively state that cold water caused the reduction in illness. Peer review of the thesis is pending.
Beyond health metrics, the research team quantified the energetic impact of cold water usage. Calculations based on standard water volume and temperature differentials show that dropping water temperature from 40 °C to 15 °C for a 45-liter shower saves 1.3 kWh of energy. Over the course of the twelve-week experiment, each adherent participant prevented the emission of nearly 15 kilograms of carbon dioxide.
The findings await full peer-reviewed evaluation following their submission to the Journal of Health Psychology. Future investigations will need to utilize randomized controlled trials with objective biomarker tracking to establish direct causality between cold water exposure and immune system function.
- Psychology thesis submitted to the Journal of Health Psychology, published October 2026.
- Prior Dutch clinical trial data on cold shower habits and workplace absence (2016).
- Immunological marker activation studies regarding cold water adaptation (2024).
