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Observational Study
. 2023 Feb 4;20(4):2773.
doi: 10.3390/ijerph20042773.

Effects of Plant-Emitted Monoterpenes on Anxiety Symptoms: A Propensity-Matched Observational Cohort Study

Davide Donelli  1   2 , Francesco Meneguzzo  3   4 , Michele Antonelli  5 , Diego Ardissino  1   2 , Giampaolo Niccoli  1   2 , Giorgio Gronchi  6 , Rita Baraldi  3 , Luisa Neri  3 , Federica Zabini  3
Affiliations
Observational Study

Effects of Plant-Emitted Monoterpenes on Anxiety Symptoms: A Propensity-Matched Observational Cohort Study

Davide Donelli et al. Int J Environ Res Public Health. .

Abstract

Immersive experiences in green areas, particularly in forests, have long been known to produce beneficial effects for human health. However, the exact determinants and mechanisms leading to healthy outcomes remain to be elucidated. The purpose of this observational cohort study was to investigate whether inhaling plant-emitted biogenic volatile compounds, namely monoterpenes (MTs), can produce specific effects on anxiety symptoms. Data from 505 subjects participating in 39 structured forest therapy sessions at different Italian sites were collected. The air concentration of monoterpenes was measured at each site. STAI state questionnaires were administered before and after the sessions as a measure of anxiety. A propensity score matching analysis was then performed, considering an above-average exposure to inhalable air MTs as the treatment. The estimated effect was -1.28 STAI-S points (95% C.I. -2.51 to -0.06, p = 0.04), indicating that the average effect of exposure to high MT air concentrations during forest therapy sessions was to decrease anxiety symptoms.

Keywords: anxiety; biogenic volatile organic compounds; forest therapy; monoterpenes; propensity matching; α-pinene.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Location of the experimental sites. Blue: remote mountain; yellow: hill; violet: remote coastal pinewood; red: urban park.
Figure 2
Figure 2
Calibration curve for α-pinene.
Figure 3
Figure 3
Average and standard deviation of MT and α-pinene concentration levels in mountain, hill, pinewood, and urban park sites.
Figure 4
Figure 4
Balance of covariates before and after propensity matching (PS weighted) for exposure to high (above the average) total monoterpenes air concentration.
Figure 5
Figure 5
Balance of covariates before and after propensity matching (PS weighted) for exposure to high (above the average) α-pinene air concentration.
Figure 6
Figure 6
Balance of covariates before and after propensity matching (PS weighted) for exposure to above-the-3rd quartile total monoterpenes air concentration.
Figure 7
Figure 7
Balance of covariates before and after propensity matching (PS weighted) for exposure to above-the-3rd quartile α-pinene air concentration.
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