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

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.

Study Overview

• Status: Recruiting
• Conditions: Monoterpene Exposure During a Forest Bathing Intervention
• Intervention / Treatment: Behavioral: Forest bathing

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Anticipated): 40
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Gregory Bratman, PhD; Phone Number: 206-543-7591; Email: bratman@uw.edu

Study Locations

• United States
  • Washington
    • Eatonville, Washington, United States, 98328
      • Recruiting
      • Pack Forest

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: All

Description

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).

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Double

Number of Arms

2

Arms and Interventions

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

What is the study measuring?

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)

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Degree of association of absorbed dose of VOCs in serum (μg/mL)	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 primary and secondary outcomes.	Up to 1 hour before the forest bathing session (1 hr); up to 1 hour after the forest bathing session (1 hr)

Collaborators and Investigators

• Sponsor: University of Washington
• Collaborators: National Center for Complementary and Integrative Health (NCCIH)
• Investigators: Principal Investigator: Gregory Bratman, PhD, University of Washington

Study record dates

Study Major Dates

• Study Start (Actual): July 12, 2022
• Primary Completion (Anticipated): September 30, 2023
• Study Completion (Anticipated): November 30, 2023

Study Registration Dates

• First Submitted: March 9, 2022
• First Submitted That Met QC Criteria: March 30, 2022
• First Posted (Actual): April 7, 2022

Study Record Updates

• Last Update Posted (Actual): November 1, 2022
• Last Update Submitted That Met QC Criteria: October 31, 2022
• Last Verified: October 1, 2022

More Information

Terms related to this study

• Other Study ID Numbers: STUDY00013134; R21AT011242 (U.S. NIH Grant/Contract)

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No