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

Not Applicable

Recruiting

• Conditions: Monoterpene Exposure During a Forest Bathing Intervention
• Interventions: Behavioral: Forest bathing

• Registration Number: NCT05316597
• Lead Sponsor: University of Washington

Brief Summary

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

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 Timeline

• Study First Submitted: 2022-03-09
• Study First Submitted QC: 2022-03-30
• Study First Posted: 2022-04-07
• Study Start: 2022-07-12
• Status Verified: 2022-10
• Last Update Submitted: 2022-10-31
• Last Update Posted: 2022-11-01
• Primary Completion: 2023-09-30
• Study Completion: 2023-11-30

Recruitment & Eligibility

• Status: RECRUITING
• Sex: All
• Target Recruitment: 40

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.

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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).

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Study & Design

• Study Type: INTERVENTIONAL
• Study Design: CROSSOVER

Arm && Interventions

Group	Intervention	Description
Terpenes On	Forest bathing	Forest bathing intervention with no filtration of terpenes from inhaled air using PAPR with particle-only filter ("terpenes on")
Terpenes Off	Forest bathing	Forest bathing intervention with filtration of terpenes from inhaled air using PAPR with activated charcoal filter ("terpenes off")

Primary Outcome Measures

Name	Time	Method
Changes in the HF (ms^2) Component of HRV	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)).	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)
Baseline HF (ms^2) Component of HRV	At baseline (pre-exposure)	Assess whether VOC inhalation regulates psychophysiological outcomes of the terpenes-on vs. terpenes-off sessions.; Ln High Frequency Heart Rate Variability at baseline.

Secondary Outcome Measures

Name	Time	Method
Blood Pressure (Diastolic in mmHg)	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)).	Assessed using mobile physiology equipment Diastolic blood pressure at T4 (60 minutes of exposure)
Beats Per Minute (BPM)	At baseline (pre-exposure).	Assessed using mobile physiology equipment BPM at baseline.
Skin Conductance (μS)	At baseline (pre-exposure).	Assessed using mobile physiology equipment Skin conductance levels at baseline.
Self-reported Positive Affect	At baseline (pre-exposure).	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
Self-reported Stress	At baseline (pre-exposure).	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
Self-reported Negative Affect	At baseline (pre-exposure).	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
Levels of CRP	At baseline (pre-exposure).	Assessed using blood serum collected via standard clinical methods. CRP levels at baseline
Levels of Cortisol in Serum (ng/mL)	At baseline (pre-exposure).	Assessed using blood serum collected via standard clinical methods Cortisol levels at baseline
Blood Pressure (Systolic in mmHg)	At baseline (pre-exposure).	Assessed using mobile physiology equipment Systolic blood pressure at baseline
Level of TNF-alpha	At baseline (pre-exposure).	Assessed using blood serum collected via standard clinical methods TNF-alpha levels at baseline
Levels of Il-6	At baseline (pre-exposure).	Assessed using blood serum collected via standard clinical methods IL-6 levels at baseline
Baseline Blood Pressure (Diastolic in mmHg)	At baseline (pre-exposure).	Assessed using mobile physiology equipment Diastolic blood pressure at baseline.

Trial Locations

Locations (1)

Pack Forest; 🇺🇸 Eatonville, Washington, United States