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

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.

Forest Therapy Research in Europe: A Scoping Review of the Scientific Literature

“…Two cohort studies meeting the inclusion criteria involved 547 participants (minimum: 42; maximum: 505; median: 273.5) [36,37]. In both of these studies, the outcomes assessed comprised the composition of the forest air and either physiological or psychological measures.…”

“…Each type of forest, including those blanketed in snow, provides a unique setting that could enhance our understanding of the therapeutic effects associated with nature experiences. Despite the current challenges in establishing clear connections between specific forest environments and psychophysiological health benefits, preliminary findings suggest that forests composed of holm oak or a mix of holm oak and pine-common in Mediterranean regions-show promising health outcomes [26,27,34,36]. Furthermore, there is some evidence to suggest that mature and ancient forests may offer greater therapeutic benefits than their younger counterparts, though this assertion is based on a single study [18].…”

“…This could inform the development of more effective forest therapy interventions. Additionally, the growing body of evidence highlighting the unique and significant role that exposure to forest-derived monoterpenes plays in enhancing psychological [36] and physiological health [37], opening up new avenues for selecting the most beneficial forest types for therapy, based especially on the emission of monoterpenes from predominant tree species.…”

From biodiversity to nature deficiency in human health and disease

“…In a recent Italian study of forest therapy, exposure to high concentrations of monoterpenes in the air relieved anxiety. 43 Urban green environments also provide favorable cardiovascular effects. 44 Data from Belgium have indicated that urban green spaces may protect against suicide mortality.…”

Virtual Forest Environment Influences Inhibitory Control

“…A growing number of studies have highlighted the significant impact of a natural environment, particularly forestry, on people's psychophysical well-being. As a matter of fact, forest exposure is associated with beneficial effects at both the physiological [1][2][3][4] and psychological levels [5][6][7][8].…”