Do Terpenes Play a Role in the Stress-reducing Effects of a Forest Bathing Intervention?

Study Overview
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Brief Summary
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This pilot study evaluates the role terpenes play in the stress-reducing effects of a forest bathing intervention. Participants will participate in two interventions in random order: 1) terpene exposure and 2) no terpene exposure.

Detailed Description
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The investigators will use an individual-level crossover design in which each session is conducted independently and on different days. Participants will be outfitted with a powered air purifying respirator (PAPR) to selectively modulate exposure to a natural suite of forest-derived volatile organic compounds (VOCs) while present in forest environments. Each participant will undergo two forest bathing sessions, one in which VOCs are not filtered (treatment condition), and one in which they are filtered (control condition). Sessions will be separated by a 7-day washout period for each participant, and order will be counterbalanced. The investigators will estimate the average effect of treatment over 40 distinct treatment days against 40 distinct control/filtered days. The power and sample size calculations (N = 40) were determined using previous nature exposure studies of similar cross-over design. The study is adequately powered assuming the conventional targets of α = 0.05 and β = 0.80 with a 10% anticipated dropout rate, and including temperature, wind, and light variability during treatment days. The specific aim of this project is to 1) assess whether VOC inhalation regulates increases in the high frequency (HF) (ms2) component of heart rate variability (HRV) as the primary outcome (with decreases in blood pressure, heart rate, self-reported stress, and levels of inflammatory cytokines in serum included as secondary outcomes); and 1a) assess the degree of association of absorbed dose of seven forest-derived VOCs in serum (i.e., α-pinene, β-pinene, β-myrcene, ∆ 3-carene, d-limonene, β- caryophyllene, α-humulene) with these outcomes.

Official Title
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Do Terpenes Play a Role in the Stress-reducing Effects of a Forest Bathing Intervention?

Conditions
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Monoterpene Exposure During a Forest Bathing Intervention

Intervention / Treatment
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* Behavioral: Forest bathing


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: 18 years and older Non-smoker Physically capable of walking for approximately 15-20 min from the study vehicle to the clinic and experimental locations. Exclusion Criteria: Pregnancy Current or prior diagnosis of neurologic, hypertensive, psychiatric, respiratory disorder, or anosmia/hyposmia Some types of medication. Olfactory sensitivity threshold (assessed via UPSIT® test kit (Sensonics International, Haddon Heights, NJ) Positive COVID-19 test At enrollment, participants will complete a baseline survey on demographics, personality traits, and regular nature contact and perceptions. Study staff will also use the clinically-validated UPSIT® test kit (Sensonics International, Haddon Heights, NJ) to evaluate olfactory sensitivity and identify/exclude participants with undiagnosed smell loss. Study staff will work with participants to schedule their forest bathing sessions and review instructions on how to prepare (e.g., by avoiding alcohol, marijuana, and certain foods, drinks, and household cleaning products with high terpene concentrations 24 hrs before their session).

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Prevention
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: Participants are assigned to both arms in random order
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Terpenes On<br>Forest bathing intervention with no filtration of terpenes from inhaled air (terpenes on) | Behavioral: Forest bathing<br>* Participants will be seated in a forest environment for an hour-long exposure to the forest<br>|
| Active Comparator: Terpenes Off<br>Forest bathing intervention with filtration of terpenes from inhaled air (terpenes off) | Behavioral: Forest bathing<br>* Participants will be seated in a forest environment for an hour-long exposure to the forest<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Changes in the HF (ms2) component of HRV | Assess whether VOC inhalation regulates psychophysiological outcomes of the terpenes-on vs. terpenes-off sessions. | up to 1 hour before the forest bathing session, during the forest bathing session (1 hr), and up to 1 hour following the forest bathing session (1hr). | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Blood pressure (systolic and diastolic in mmHg) | Assessed using mobile physiology equipment | up to 2.5 hours before the forest bathing session, during the forest bathing session (1 hr), and up to 1 hour following the forest bathing session (1hr). | 
| Heart rate (beats per minute) | Assessed using mobile physiology equipment | up to 2.5 hours before the forest bathing session, during the forest bathing session (1 hr), and up to 1 hour following the forest bathing session (1hr). | 
| Skin conductance (μS) | Assessed using mobile physiology equipment | up to 2.5 hours before the forest bathing session, during the forest bathing session (1 hr), and up to 1 hour following the forest bathing session (1hr). | 
| Self-reported affect | Assessed using the shortened Positive and Negative Affect Schedule (PANAS) and/or Profile of Mood States (POMS) | up to 2.5 hours before the forest bathing session, during the forest bathing session (1 hr), and up to 1 hour following the forest bathing session (1hr). | 
| Self-reported anxiety | Assessed using the shortened State-Trait Anxiety Inventory (STAI) | up to 2.5 hours before the forest bathing session, during the forest bathing session (1 hr), and up to 1 hour following the forest bathing session (1hr). | 
| Self-reported stress | Assessed using Perceived Stress Scale 4 (PSS-4) | up to 2.5 hours before the forest bathing session, during the forest bathing session (1 hr), and up to 1 hour following the forest bathing session (1hr). | 
| Levels of inflammatory cytokines (CRP, TNF-alpha, and IL-6 in μg/mL) | Assessed using blood serum collected via standard clinical methods | Up to 1 hour before the forest bathing session (1 hr); up to 1 hour after the forest bathing session (1 hr) | 
| Levels of cortisol in serum (μg/mL) | Assessed using blood serum collected via standard clinical methods | Up to 1 hour before the forest bathing session (1 hr); up to 1 hour after the forest bathing session (1 hr) |