Does waterfall aerosol influence mucosal immunity and chronic stress? A randomized controlled clinical trial

Abstract

Background: The specific microclimate of alpine waterfalls with high levels of ionized water aerosols has been suggested to trigger beneficial immunological and psychological effects. In the present three-armed randomized controlled clinical study, we focused on effects on (i) immunological reagibility, on (ii) physiological stress responses, and on (iii) stress-related psychological parameters.

Methods: People with moderate to high stress levels (n = 65) spent an active sojourn with daily hiking tours in the National Park Hohe Tauern (Großkirchheim, Austria). Half of the group was exposed to water aerosol of an alpine waterfall for 1 h/day (first arm, n = 33), whereas the other half spent the same time at a distant site (second arm, n = 32). A third arm (control, n = 26) had no intervention (except vaccination) and stayed at home, maintaining their usual lifestyle. The effect of the interventions on the immune system was tested by oral vaccination with an approved cholera vaccine and measuring specific salivary IgA antibody titers. Lung function was determined by peak expiratory flow measurement. Electric skin conductance, heart rate, and adaption of respiration rate were assessed as physiological stress parameters. Psychological stress-related parameters were analyzed by questionnaires and scales.

Results: Compared to the control group, both intervention groups showed improvement of the lung function and of most physiological stress test parameters. Analysis of the mucosal immune response revealed a waterfall-specific beneficial effect with elevated IgA titers in the waterfall group. In line with these results, exposure to waterfall revealed an additional benefit concerning psychological parameters such as subjective stress perception (measured via visual analog scale), the Global Severity Index (GSI), and the Positive Symptom Total (PST).

Conclusions: Our study provides new data, which strongly support an "added value" of exposure to waterfall microclimate when combined with a therapeutic sojourn at high altitude including regular physical activity.

Keywords: Alpine space; Burnout prevention; Chronic stress; Green exercise; High-altitude climate therapy; Ionized water aerosol; Mountain hiking; Mucosal immune response; Waterfall.

Fig. 1

Study schedule. Schematic chronological process of the controlled clinical trial

Fig. 2

IgA levels of all groups. Antigen-specific salivary IgA levels of responders. Linear mixed model (LMM1) of both intervention groups compared to the control group. Significance are indicated by p values. Data are shown in percentage change (±SD) from baseline (pre-serum)

Fig. 3

IgA levels of the two intervention groups. Antigen-specific salivary IgA levels of responders. Linear mixed model (LMM2) of the waterfall group (WF+) compared to the non-waterfall group (WF−). Significances are indicated by p values. Data are shown in percentage change (±SD) from baseline (pre-serum)

Fig. 4

Subjective stress perception. Visual analog scale of subjective stress perception. Stress levels in the WF+ group were significantly decreased (compared to control) and shown a trend to a specific waterfall effect (WF+ to CO p = 0.000, R ² = 0.615; WF+ to WF−: p = 0.054, R ² = 0.179; WF– to CO p = 0.066, R ² = 0.496). Data shown in means (±SD). Statistical analysis calculated with linear regression

Fig. 5

SCL-90 questionnaire. Results of the SCL-90 questionnaire shown in percentage change from baseline. The data indicate beneficial effects of both interventions, with stronger significances for the waterfall group. Linear mixed models of the three study groups over time. Data shown in means (±SD)

Fig. 6

Global Severity Index and Positive Symptom Total Score of the SCL-90. Global indices of the SCL-90 questionnaire. The data show significant improvements of the Global Severity Index and the Positive Symptom Total score (PST p = 0.03, GSI p = 0.009) in the WF+ group on day 6. Data shown in percentage change from baseline (±SD)

Fig. 7

Lung function and physiological stress test. Linear regression analysis of lung function and peripheral signals of the physiological stress test. Spirometry was performed measuring peak expiratory flow (PEF), as peripheral signals of physiological stress served heart rate (HR), skin conductance (SC), and respiration rate (RSP). Means (±SD) of the PEF value is shown in percent of the predicted PEF, scaled on age, height, weight, gender, smoker (yes, no, former), and asthma (yes, no). Means (±SD) of the 4-min post-stress recovery phase shown in percentage compared to means of the 1-min stressor phase (100% reference, indicated as red line)