CompletedNCT05316597Updated Sep 19, 2024Results posted

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

An interventional study of Forest bathing in Monoterpene Exposure During a Forest Bathing Intervention, sponsored by University of Washington. Completed at 1 site in United States. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2024-09-19.

Sponsored by University of Washington · Not applicable, Interventional, and Prevention

Phase: Not applicable
Study type: Interventional
Enrollment: 43
Allocation: Randomized
Ages: 18 Years and older
Sex: All

Study 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.

Read the 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.

Conditions studied

Monoterpene Exposure During a Forest Bathing Intervention

In context

Lead sponsor

University of Washington is the lead sponsor of 1,431 studies on the registry; 226 are open to participants now.

Of its 158 completed or terminated interventional studies of FDA-regulated products, 136 (86%) have results posted.

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Who can participate

Ages eligible: 18 Years and older
Sexes eligible: All
Accepts healthy volunteers: Yes

Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.

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

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 design

Phase: Not applicable
Primary purpose: Prevention
Allocation: Randomized
Intervention model: Crossover assignment
Masking: Double (Participant, Investigator)
Enrollment: 43 participants (actual)

Study arms

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
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

Interventions

BehavioralForest bathing
Participants will be seated in a forest environment for an hour-long exposure to the forest

What researchers measure

Primary outcomes

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)
Time frame: 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.
Time frame: At baseline (pre-exposure)

Secondary outcomes

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

Other outcomes

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 frame: 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.

Results

Posted Sep 19, 2024

Participant flow

First Session

Participant flow — First Session
Milestone	Terpenes On, Then Terpenes Off	Terpenes Off, Then Terpenes On
Started	21	22
Completed	21	21
Not completed	0	1
Withdrew: Withdrawal by subject	0	1

Washout Period

Participant flow — Washout Period
Milestone	Terpenes On, Then Terpenes Off	Terpenes Off, Then Terpenes On
Started	21	21
Completed	18	13
Not completed	3	8
Withdrew: Lost to follow-up	1	2
Withdrew: Physician decision	1	1
Withdrew: Excluded before second session	1	1
Withdrew: Withdrawal by subject	0	4

Second Session

Participant flow — Second Session
Milestone	Terpenes On, Then Terpenes Off	Terpenes Off, Then Terpenes On
Started	18	13
Completed	18	13
Not completed	0	0

Outcome measures

PrimaryChanges 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)

Time frame:: 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)).
Reported as:: Mean · ms^2

Changes in the HF (ms^2) Component of HRV
ms^2	Terpenes On	Terpenes Off
Changes in the HF (ms^2) Component of HRV	6.65 ± 1.33	6.48 ± 1.14

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.914 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): 0.01Control for that session's baseline included in the mixed model.

SecondaryBlood Pressure (Diastolic in mmHg)

Assessed using mobile physiology equipment Diastolic blood pressure at T4 (60 minutes of exposure)

Time frame:: 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)).
Reported as:: Mean · mmHg

Blood Pressure (Diastolic in mmHg)
mmHg	Terpenes On	Terpenes Off
Blood Pressure (Diastolic in mmHg)	75.4 ± 9.86	73.2 ± 11.1

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = .554 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): 1.13Control for that session's baseline included in the mixed model.

SecondaryBeats Per Minute (BPM)

Assessed using mobile physiology equipment BPM at time point 4 (60 minutes of exposure)

Time frame:: 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)).
Reported as:: Mean · BPM

Beats Per Minute (BPM)
BPM	Terpenes On	Terpenes Off
Beats Per Minute (BPM)	61.4 ± 11.9	63.0 ± 13.7

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.905 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): 0.13

SecondarySkin Conductance (μS)

Assessed using mobile physiology equipment Skin conductance levels at time point 2 (20 minutes into exposure)

Time frame:: 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)).
Reported as:: Mean · microsiemens (µS)

Skin Conductance (μS)
microsiemens (µS)	Terpenes On	Terpenes Off
Skin Conductance (μS)	3.28 ± 3.76	4.14 ± 5.94

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.076 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): -0.84Control for that session's baseline included in the mixed model.
Terpenes On vs Terpenes Off · ANOVA · p = 0.02 (Threshold of P \< 0.05 for significance. ANCOVA results of comparing reduced vs. full model over time.)

SecondarySelf-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

Time frame:: 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)).
Reported as:: Mean · Score on a scale

Self-reported Positive Affect
Score on a scale	Terpenes On	Terpenes Off
Self-reported Positive Affect	12.1 ± 4.00	11.3 ± 4.38

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.210 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): 0.70Control for that session's baseline included in the mixed model.
Terpenes On vs Terpenes Off · ANOVA · p = 0.57 (Threshold of P \< 0.05 for significance. ANCOVA results of comparing reduced vs. full model over time.)

SecondarySelf-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

Time frame:: 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)).
Reported as:: Mean · Score on a scale

Self-reported Stress
Score on a scale	Terpenes On	Terpenes Off
Self-reported Stress	1.09 ± 0.390	1.17 ± 0.447

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.921 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): 0.01Control for that session's baseline included in the mixed model.
Terpenes On vs Terpenes Off · ANOVA · p = 0.82 (Threshold of P \< 0.05 for significance. ANCOVA results of comparing reduced vs. full model over time.)

SecondarySelf-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

Time frame:: 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)).
Reported as:: Mean · Score on a scale

Self-reported Negative Affect
Score on a scale	Terpenes On	Terpenes Off
Self-reported Negative Affect	5.13 ± 0.421	5.31 ± 0.749

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.265 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): -0.16Control for that session's baseline included in the mixed model.
Terpenes On vs Terpenes Off · ANOVA · p = 0.63 (Threshold of P \< 0.05 for significance. ANCOVA results of comparing reduced vs. full model over time.)

SecondaryLevels of CRP

Assessed using blood serum collected via standard clinical methods. CRP levels at time point 4 (60 minutes of exposure).

Time frame:: 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)).
Reported as:: Mean · mg/L

Levels of CRP
mg/L	Terpenes On	Terpenes Off
Levels of CRP	9.99 ± 7.83	13.4 ± 12.5

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.724 (a priori threshold for statistical significance = p \< 0.05.) · Median difference (final values): -0.34Control for that session's baseline included in the mixed model.

SecondaryLevels 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).

Time frame:: 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)).
Reported as:: Mean · ng/mL

Levels of Cortisol in Serum (ng/mL)
ng/mL	Terpenes On	Terpenes Off
Levels of Cortisol in Serum (ng/mL)	98.6 ± 43.6	109.0 ± 60.0

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.716 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): -2.85Control for that session's baseline included in the mixed model.

SecondaryBlood Pressure (Systolic in mmHg)

Assessed using mobile physiology equipment Systolic blood pressure at T4 (60 minutes of exposure)

Time frame:: 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)).
Reported as:: Mean · mmHg

Blood Pressure (Systolic in mmHg)
mmHg	Terpenes On	Terpenes Off
Blood Pressure (Systolic in mmHg)	123 ± 16.9	121 ± 14.0

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.852 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): -0.53Control for that session's baseline included in the mixed model.

SecondaryLevel of TNF-alpha

Assessed using blood serum collected via standard clinical methods TNF-alpha levels at time point 4 (60 minutes of exposure).

Time frame:: 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)).
Reported as:: Mean · pg/mL

Level of TNF-alpha
pg/mL	Terpenes On	Terpenes Off
Level of TNF-alpha	3.80 ± 2.71	4.27 ± 2.84

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.166 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): -0.79Control for that session's baseline included in the mixed model.

SecondaryLevels of Il-6

Assessed using blood serum collected via standard clinical methods IL-6 levels at time point 4 (60 minutes of exposure).

Time frame:: 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)).
Reported as:: Mean · pg/mL

Levels of Il-6
pg/mL	Terpenes On	Terpenes Off
Levels of Il-6	0.547 ± 0.609	0.763 ± 0.820

Statistical analysis

Terpenes On vs Terpenes Off · Mixed Models Analysis · p = 0.046 (a priori threshold for statistical significance = p \< 0.05.) · Mean difference (final values): -0.19Control for that session's baseline included in the mixed model.

Other pre-specifiedDegree 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 frame:: 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.
Reported as:: Number · correlation coefficient

Degree of Association of Sum Composite of Absorbed Dose of VOCs in Serum (μg/mL)
correlation coefficient	All Participants
Ln-HR HRV	1.06 (-0.38 to 2.5)
SCL	-7.31 (-14.6 to -0.03)
DBP	11.89 (-4.65 to 28.42)
SBP	17.55 (-7.77 to 42.88)
HR	7.16 (-5.8 to 20.11)
PA	3.75 (-3.6 to 11.09)
NA	0.15 (-1.11 to 1.4)
Self-reported stress	-0.38 (-1.66 to 0.89)
Cortisol	-45.45 (-150.06 to 59.17)
Il-6	-0.60 (-1.63 to 0.43)
TNF-alpha	-5.73 (-10.95 to -0.51)
CRP	-0.70 (-1.64 to 0.25)

PrimaryBaseline 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.

Time frame:: At baseline (pre-exposure)
Reported as:: Mean · ms^2

Baseline HF (ms^2) Component of HRV
ms^2	Terpenes On	Terpenes Off
Baseline HF (ms^2) Component of HRV	6.48 ± 1.40	6.34 ± 1.55

SecondaryBaseline Blood Pressure (Diastolic in mmHg)

Assessed using mobile physiology equipment Diastolic blood pressure at baseline.

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · mmHg

Baseline Blood Pressure (Diastolic in mmHg)
mmHg	Terpenes On	Terpenes Off
Baseline Blood Pressure (Diastolic in mmHg)	67.8 ± 10.8	66.1 ± 11.0

SecondaryBeats Per Minute (BPM)

Assessed using mobile physiology equipment BPM at baseline.

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · BPM

Beats Per Minute (BPM)
BPM	Terpenes On	Terpenes Off
Beats Per Minute (BPM)	66.3 ± 13.0	66.6 ± 13.3

SecondarySkin Conductance (μS)

Assessed using mobile physiology equipment Skin conductance levels at baseline.

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · microsiemens (µS)

Skin Conductance (μS)
microsiemens (µS)	Terpenes On	Terpenes Off
Skin Conductance (μS)	3.58 ± 3.94	3.84 ± 5.14

SecondarySelf-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

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · Score on a scale

Self-reported Positive Affect
Score on a scale	Terpenes On	Terpenes Off
Self-reported Positive Affect	12.0 ± 3.74	12.2 ± 4.59

SecondarySelf-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

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · Score on a scale

Self-reported Stress
Score on a scale	Terpenes On	Terpenes Off
Self-reported Stress	1.44 ± 0.698	1.57 ± 0.817

SecondarySelf-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

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · Score on a scale

Self-reported Negative Affect
Score on a scale	Terpenes On	Terpenes Off
Self-reported Negative Affect	5.81 ± 1.11	5.92 ± 1.46

SecondaryLevels of CRP

Assessed using blood serum collected via standard clinical methods. CRP levels at baseline

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · mg/L

Levels of CRP
mg/L	Terpenes On	Terpenes Off
Levels of CRP	9.93 ± 6.43	13.6 ± 13.7

SecondaryLevels of Cortisol in Serum (ng/mL)

Assessed using blood serum collected via standard clinical methods Cortisol levels at baseline

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · ng/mL

Levels of Cortisol in Serum (ng/mL)
ng/mL	Terpenes On	Terpenes Off
Levels of Cortisol in Serum (ng/mL)	117 ± 57.8	124 ± 55.1

SecondaryBlood Pressure (Systolic in mmHg)

Assessed using mobile physiology equipment Systolic blood pressure at baseline

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · mmHg

Blood Pressure (Systolic in mmHg)
mmHg	Terpenes On	Terpenes Off
Blood Pressure (Systolic in mmHg)	119 ± 12.4	117 ± 13.9

SecondaryLevel of TNF-alpha

Assessed using blood serum collected via standard clinical methods TNF-alpha levels at baseline

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · pg/mL

Level of TNF-alpha
pg/mL	Terpenes On	Terpenes Off
Level of TNF-alpha	4.03 ± 2.75	3.72 ± 2.64

SecondaryLevels of Il-6

Assessed using blood serum collected via standard clinical methods IL-6 levels at baseline

Time frame:: At baseline (pre-exposure).
Reported as:: Mean · pg/mL

Levels of Il-6
pg/mL	Terpenes On	Terpenes Off
Levels of Il-6	0.585 ± 0.569	0.591 ± 0.776

Adverse events

Collected over Monitoring from pre-exposure time (i.e., meeting participants for each session, driving to forest location, application of physiology equipment, serum collection, and self-report assessments (total of ~2-4 hours)) through duration of 60 min forest exposure sessions and subsequent period after session completion (i.e., debriefing, and returning of participants from forest session location to initial meeting point (total of ~1.5-2.5 hours)).. Non-serious events are listed at a 5% frequency threshold.

Adverse event summary by group
Group	Deaths	Serious	Other
Terpenes On	0/43 (0%)	0/43 (0%)	0/43 (0%)
Terpenes Off	0/43 (0%)	0/43 (0%)	0/43 (0%)

Baseline characteristics

Age, Continuous
Age, Continuous(years)	Terpenes On, Then Terpenes Off	Terpenes Off, Then Terpenes On	Total
Mean	33.0 ± 14.2	37.1 ± 14.5	35.1 ± 14.3

Sex/Gender, Customized
Sex/Gender, Customized(Participants)	Terpenes On, Then Terpenes Off	Terpenes Off, Then Terpenes On	Total
Male	7	10	17
Female	12	10	22
Prefer to self-describe/non-binary	2	2	4

Ethnicity (NIH/OMB)
Ethnicity (NIH/OMB)(Participants)	Terpenes On, Then Terpenes Off	Terpenes Off, Then Terpenes On	Total
Hispanic or Latino	2	3	5
Not Hispanic or Latino	19	19	38
Unknown or Not Reported	0	0	0

Race (NIH/OMB)
Race (NIH/OMB)(Participants)	Terpenes On, Then Terpenes Off	Terpenes Off, Then Terpenes On	Total
American Indian or Alaska Native	0	1	1
Asian	2	3	5
Native Hawaiian or Other Pacific Islander	0	0	0
Black or African American	1	2	3
White	16	15	31
More than one race	0	0	0
Unknown or Not Reported	2	1	3

Region of Enrollment
Region of Enrollment(participants)	Terpenes On, Then Terpenes Off	Terpenes Off, Then Terpenes On	Total
United States	21	22	43

Study locations

1 site

Pack Forest
Eatonville, Washington 98328, United States

References and documents

Study documents

Study protocol · May 7, 2024
Statistical analysis plan · May 7, 2024
Informed consent form · Jul 25, 2023

Documents are hosted by the registry — open the source record to download them.

Timeline

Tracking since Sep 25, 2026

ElapsedEstimatedEstimated, not yet reached

Ran from Jul 2022 to primary completion in Sep 2023, 14 months.

Results were first posted in Sep 2024, 11 months after primary completion.

How these figures are worked out, and which studies are left out of them.

Registered: Mar 9, 2022
First posted: Apr 7, 2022
StartActual: Jul 12, 2022
Primary completionActual: Sep 21, 2023
CompletionActual: Sep 21, 2023
Results first posted: Sep 19, 2024
Last update: Sep 19, 2024

What these dates mean

Start.: When the first participant enrolled; while estimated, when the study expects to open to recruitment.
Primary completion.: When the last participant was examined or treated to collect data for the study's main question, its primary outcome. A study that stopped early gives the date its data collection stopped.
Completion.: When the last participant's last visit took place, for every outcome, secondary ones and side effects included: the end of the study. Often later than primary completion, sometimes the same day.
Actual and Est.: Actual means the registry says the date has happened. Est. (estimated) is a date the sponsor plans or expects. It can still move, and the sponsor is expected to change it to actual once it has passed.

No changes since tracking began. The registry record was last updated on Sep 19, 2024, before this site started recording changes on Sep 25, 2026. Its history is on ClinicalTrials.gov ↗

Registry details

Key details

Study ID: NCT05316597
Lead sponsor: University of Washington
Collaborators: National Center for Complementary and Integrative Health (NCCIH)
Responsible party: Gregory Bratman (Assistant Professor: Environmental and Forest Sciences, University of Washington) — Principal investigator
First posted: Apr 7, 2022
Start date: Jul 12, 2022
Primary completion: Sep 21, 2023
Completion: Sep 21, 2023
Results posted: Sep 19, 2024
Last update: Sep 19, 2024

Study contacts

Gregory Bratman, PhD

principal investigator · University of Washington

Oversight

Data monitoring committee: Yes
FDA-regulated drug: No
FDA-regulated device: No

View the source record on ClinicalTrials.gov ↗

Not currently enrolling

This study is completed, as verified in Aug 2024. You cannot join it, but the record below documents what was studied.

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