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: Completed
• 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 washout period of at least 8 days 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 six forest-derived VOCs (i.e., α-pinene, β-pinene, β-myrcene, Δ-3-carene, limonene, β- carophyllene) in serum with these outcomes.

• Study Type: Interventional
• Enrollment (Actual): 43
• Phase: Not Applicable

Contacts and Locations

Study Locations

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

Participation Criteria

Eligibility Criteria

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

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)

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 using PAPR with particle-only filter ("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 using PAPR with activated charcoal filter ("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 (ms^2) Component of HRV	Assess whether VOC inhalation regulates psychophysiological outcomes of the terpenes-on vs. terpenes-off sessions. Ln High Frequency Heart Rate Variability at T2 (20 minutes into duration of exposure for each session)	At time point 2 (20 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Baseline HF (ms^2) Component of HRV	Assess whether VOC inhalation regulates psychophysiological outcomes of the terpenes-on vs. terpenes-off sessions. Ln High Frequency Heart Rate Variability at baseline.	At baseline (pre-exposure)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Blood Pressure (Diastolic in mmHg)	Assessed using mobile physiology equipment Diastolic blood pressure at T4 (60 minutes of exposure)	At time point 4 (60 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Beats Per Minute (BPM)	Assessed using mobile physiology equipment BPM at time point 4 (60 minutes of exposure)	At time point 4 (60 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Skin Conductance (μS)	Assessed using mobile physiology equipment Skin conductance levels at time point 2 (20 minutes into exposure)	At time point 2 (20 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Self-reported Positive Affect	Assessed using the shortened Positive and Negative Affect Schedule (PANAS) Positive affect at time point 2 (20 minutes of exposure) Higher scale scores are indicative of better outcome Range 5-50	At time point 2 (20 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Self-reported Stress	Assessed using a single-item self report non-validated scale Self-reported stress at time point 2 (20 minutes of exposure) Higher scale score indicative of worse outcome Range 1-5	At time point 2 (20 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Self-reported Negative Affect	Assessed using the shortened Positive and Negative Affect Schedule (PANAS) Negative affect at time point 2 (20 minutes of exposure) Higher score on scale indicative of worse outcome Range 5-50	At time point 2 (20 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Levels of CRP	Assessed using blood serum collected via standard clinical methods. CRP levels at time point 4 (60 minutes of exposure).	At time point 4 (60 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Levels of Cortisol in Serum (ng/mL)	Assessed using blood serum collected via standard clinical methods Cortisol levels at time point 4 (60 minutes of exposure).	At time point 4 (60 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Blood Pressure (Systolic in mmHg)	Assessed using mobile physiology equipment Systolic blood pressure at T4 (60 minutes of exposure)	At time point 4 (60 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Level of TNF-alpha	Assessed using blood serum collected via standard clinical methods TNF-alpha levels at time point 4 (60 minutes of exposure).	At time point 4 (60 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Levels of Il-6	Assessed using blood serum collected via standard clinical methods IL-6 levels at time point 4 (60 minutes of exposure).	At time point 4 (60 minutes into duration of exposure for Session 1 and Session 2 (which occurred at least 8 days after Session 1)).
Baseline Blood Pressure (Diastolic in mmHg)	Assessed using mobile physiology equipment Diastolic blood pressure at baseline.	At baseline (pre-exposure).
Beats Per Minute (BPM)	Assessed using mobile physiology equipment BPM at baseline.	At baseline (pre-exposure).
Skin Conductance (μS)	Assessed using mobile physiology equipment Skin conductance levels at baseline.	At baseline (pre-exposure).
Self-reported Positive Affect	Assessed using the shortened Positive and Negative Affect Schedule (PANAS) Positive affect at baseline Higher scale scores are indicative of better outcome Range 5-50	At baseline (pre-exposure).
Self-reported Stress	Assessed using a single-item self report non-validated scale Self-reported stress at baseline Higher scale score indicative of worse outcome Range 1-5	At baseline (pre-exposure).
Self-reported Negative Affect	Assessed using the shortened Positive and Negative Affect Schedule (PANAS) Negative affect at baseline Higher score on scale indicative of worse outcome Range 5-50	At baseline (pre-exposure).
Levels of CRP	Assessed using blood serum collected via standard clinical methods. CRP levels at baseline	At baseline (pre-exposure).
Levels of Cortisol in Serum (ng/mL)	Assessed using blood serum collected via standard clinical methods Cortisol levels at baseline	At baseline (pre-exposure).
Blood Pressure (Systolic in mmHg)	Assessed using mobile physiology equipment Systolic blood pressure at baseline	At baseline (pre-exposure).
Level of TNF-alpha	Assessed using blood serum collected via standard clinical methods TNF-alpha levels at baseline	At baseline (pre-exposure).
Levels of Il-6	Assessed using blood serum collected via standard clinical methods IL-6 levels at baseline	At baseline (pre-exposure).

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Degree of Association of Sum Composite of Absorbed Dose of VOCs in Serum (μg/mL)	Assess the association of absorbed dose (µg/mL) of forest-derived VOCs in serum with primary and secondary outcomes.	Time point 4 (60 min) for absorbed dose associations with same time point for DBP, SBP, Cortisol, Il-6, TNF-alpha, and CRP; and associations with Time point 2 (20 minutes) for HRV, SCL, positive affect, negative affect, self-reported stress, heart rate.

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 (Actual): September 21, 2023
• Study Completion (Actual): September 21, 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): September 19, 2024
• Last Update Submitted That Met QC Criteria: August 21, 2024
• Last Verified: August 1, 2024

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