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Table 2 Medical empirical research (n = 25)

From: Medical empirical research on forest bathing (Shinrin-yoku): a systematic review

Authors (year) Research design Participants Intervention measures Control measures Measurements and outcomes
Trial group Control group Self-report measures Physiological measures
Horiuchi (2015) [19] NRCT (before-after study) ※ 1) Response group: Male and female participants, average age was 63.9 years (n = 27). 2) Non-response group: Male and female participants, average age was 61.6 years (n = 27). N/A Participants were exposed to forest environment and the activity was carried out for 90 min 1) Participants were divided into 2 groups according to the changes of mean arterial pressure before and after forest bathing (>5% was the response group, <5% was the non-response group).
2) Some participants were given medications for hypertension, diabetes, hyperlipidemia, hyperuricemia, and osteoporosis.
3) Smoking and caffeine were banned 12 h before the trial, and alcohol was banned 24 h before the trial
1) Response group
POMS:
D*↓
V*↑
T-A*↓
F*↓
C*↓
A-H*↓
2) Non-response group
POMS:
D*↓
V*↑
T-A*↓
F*↓
C*↓
A-H↓
1) Response group:
SBP*↓
DBP*↓
Mean arterial pressure*↓
Salivary amylase↓
2) Non-response group:
SBP*↓
DBP↓
Mean arterial pressure*↓
Salivary amylase↑
Igarashi (2015) [20] RCT (cross-over study) ※ Female participants, average age was 46.1 years (n = 4 or 1) Female participants, average age was 46.1 years (n = 4 or 1) After a 3-min rest, the participants sat and watched the kiwi orchard for 10 min (or the building site); after a 3-min rest, the participants sat and watched the building site (or the kiwi orchard), each group was asked to view 2 trial sites 1) The trial began in the summer. 2) Seventeen participants were divided into five groups. 3) Participants avoided menstruation and did not drink or smoke. 4) Lived in the suburbs. 5) The two trial sites are close to each other SD method:
Comfortable feeling#
Natural feeling#
Relaxed feeling#
POMS:
D#
V#
T-A#
F#
C#
A-H #
lnHF #↑
lnLF/lnHF↓
Heart rate↓
Kang (2015) [21] RCT Male and female participants, average age was 54.8 years (n = 32) Male and female participants, average age was 50 years (n = 32) In the morning, the trial group and control group were exposed to the forest environment and walked for 2 h In the afternoon, the trial group performed additional stretching and intensive exercises for 4 h 1) The trial began in late spring and lasted five days. 2) Participants selection criteria: Adults over 20 years of age with posterior neck pain for more than 3 months, and VAS grades over 4 VAS:
VAS on the first day*↓
VAS on the end day*↓
Cervical range of motion*↑
Neck disability index*↓
EuroQol 5D-3 L VAS*↑
EuroQol 5D-3 L index*↑
McGill pain questionnaire*↓
Trigger points in the posterior neck region#
N/A
Ochiai (2015a) [22] NRCT (before-after study) ※ Male participants with high normal blood pressure, age range 40–72 years (n = 9) N/A On trial day, participants were exposed to forest environment for activities and rest from 10:30 to 15:05 1) The trial was carried out in early autumn, and the average air temperature was 21.5 °C. 2) No alcohol or conversation was allowed during the trial, and cell phones were allowed only during breaks SD method:
Comfortable feeling↑
Natural feeling*↑
Relaxed feeling*↑
POMS:
D↓
V↓
T-A*↓
F↓
C*↓
A-H*↓
POMS total mood disturbance*↓
SBP*↓
DBP*↓
Urinary adrenaline levels *↓
Serum cortisol levels *↓
Ochiai (2015b) [23] NRCT (before-after study) ※ Female participants, the average age was 62.2 years (n = 17) N/A On trial day, participants were exposed to forest environment for activities and rest from 10:32 to 15:13 1) The trial was carried out in summer, and the average air temperature was 21.5 °C. 2) Except for 6 participants who were taking medication to control their blood pressure, the rest of the participants had no other physical or psychological diseases. 3) No alcohol or cell phones were allowed during the trial SD method:
Comfortable feeling*↑
Natural feeling*↑
Relaxed feeling*↑
POMS:
T-A*↓
F↓
V*↑
Pulse rate*↓
Salivary cortisol concentration *↓
Song (2015a) [24] RCT (cross-over study) ※ Male participants, the average age was 21.5 years (n = 6) Male participants, the average age was 21.5 years(n = 6) Day 1, the trial group was exposed to forest environment and walked for 15 min, while the control group was exposed to urban environment and walked for 15 min. Day 2, the two groups interchanged environments 1) The trial lasted for 2 days. 2) Smoking and drinking are prohibited during the trial. 3) The trial was conducted several times and a total of 92 participants participated N/A If the participants had high initial blood pressure and pulse, forest walking could reduce these two indicators. The results were reversed if the participants had lower initial blood pressure and pulse
Song (2015b) [25] RCT (cross-over study) ※ Male participants with hypertension or high normal blood pressure, the average age was 58 years (n = 10) Male participants with hypertension or high normal blood pressure, the average age was 58 years(n = 10) Day 1, the trial group was exposed to forest environment and walked for 17 min, while the control group was exposed to urban environment and walked for 17 min. Day 2, the two groups interchanged environments 1) The trial lasted for 2 days. 2) When the trial was carried out, the average air temperature in the forest was 21.4 °C, and that in the city was 28.1 °C. 3) Smoking, alcohol and caffeine consumption were prohibited during the trial. 4) Participants who were on medication were excluded. 5) Trial at the same time every day SD method:
Comfortable feeling#
Natural feeling#
Relaxed feeling#
POMS:
D#
V#
T-A#
F#
C#
A-H#
lnHF #
Pulse rate#
Im
(2016) [26]
RCT (cross-over study) ※+ Male and female participants, age range 18–35 years (n = 19) Male and female participants, the age range 18–35 years(n = 22) In the morning, the trial group was exposed to forest environment for 2 h, while the control group was exposed to urban environment for 2 h. In the afternoon, the two groups interchanged environments 1) The trial began in the summer. 2) The participants had no mental illness, allergic rhinitis or bronchitis. 3) Bachelor’s degree or above and live in city. 4) To avoid carryover effect, the interval between morning trial and afternoon trial was 2 h. 5) Alcohol consumption was restricted 12 h before the test, and food consumption was restricted 1 h before the test. Smoking and drinking were prohibited during the test, and electronic products were restricted. 6) All groups had the same diet Stress response inventory:
Total#
Somatic symptoms#
Depressive symptoms#
Anger symptoms↓
IL-6↑
IL-8#
TNF-α#
GPx#
Jia
(2016) [27]
RCT※ Male and female participants with COPD (n = 10) Male and female participants with COPD (n = 8) In the morning, the trial group was exposed to forest environment and walked for 90 min, while the control group was exposed to urban environment and walked for 90 min. Afternoon is the same as morning 1) The trial began in the summer. 2) The participants did not have acute exacerbation. 3) Participants have the same accommodation and schedule. 4) The trial lasted for 4 days POMS:
D*↓
V↑
T-A*#
F↓
C↓
A-H*↓
NK cells *↓
CD8+ T-lymphocytes expressing perforin *#
NKT-like cells *#
IL-6*#
IL-8*#
Interferon-γ*#
TNF-α↓
IL-1β#
CRP#
Pulmonary and activation-regulated chemokine*#
Tissue inhibitor of metalloproteinase-1*#
Surfactant protein D #
Cortisol#
Epinephrine*#
Li
(2016) [28]
NRCT※ Male participants with hypertension or high normal blood pressure, age range 40–69 years (n = 19) Male participants with hypertension or high normal blood pressure, age range 40–69 years (n = 19) In the first trial, the control group was exposed to urban environment and walked 2.6 km. In the second trial, the control group was exposed to forest environment and walked 2.6 km 1) The trial began in the summer. 2) Participants did not take any antihypertensive drugs. 3) No alcohol was allowed and the diet was the same during the trial. 4) The interval between the two trials was one week POMS:
D#
V#
T-A#
F#
C#
A-H!
SBP!
DBP!
Pulse rate #
Triglycerides!
Cho!
LDL-Cho!
HDL-Cho!
Remnant-like particles Cho!
Adiponectin#
Glycated hemoglobin!
Blood glucose!
Insulin!
Dehydroepiandrosterone sulfate!
CRP!
Epinephrine↓
Norepinephrine *#
Dopamine#
Bang (2017) [29] NRCT※ Male and female participants, the average age was 24.8 years (n = 51) Male and female participants, the average age was 23.8 years (n = 48) The participants walked in the campus forest once a week for 40 min 1) The trial began in the autumn. 2) The trial lasted for 6 weeks. 3) The trial group received extra messages of encouragement during the trial and attended a stress management seminar Health-promoting
Lifestyle profile II:
Total#
Responsibility for health#
Physical activity↑
Healthy nutrition↑
Social relations↑
Stress management#
Spiritual growth↑
BDI score#
SBP #↑
DBP↑
Cho↓
HDL-Cho↓
LDL-Cho↑
Triglycerides#
Bone density#
Body Mass Index↑
Percent of body fat↑
lnLF/lnHF↑
Parasympathetic nerve activity↑
Chun (2017) [30] RCT※+ Male and female participants with chronic stroke, the average age was 60.8 years (n = 30) Male and female participants with chronic stroke, the average age was 60.8 years (n = 29) The trial group was exposed to forest environment for meditation and walking. The control group was exposed to urban environment for meditating and walking 2) The trial lasted for 4 days BDI score*#
Score of 17-item version of the Hamilton Depression Rating Scale*#
STAI score*#
Reactive oxygen metabolites↓
Biological antioxidant potential*#
Kobayashi (2017) [31] RCT (cross-over study)※ Male participants, the average age was 21.7 years (n = 12) Male participants, the average age was 21.7 years (n = 12) Day 1, the trial group was exposed to forest environment, while the control group was exposed to urban environment. Day 2, the two groups interchanged environments 1) The trial began in the summer and early autumn. 2) The trial lasted for 2 days. 3) 34 forests and cities were selected for the trial, and a total of 34 trials were carried out N/A Salivary cortisol concentration#
Mao
(2017) [32]
RCT※ Male and female participants with chronic heart failure, age range 65–80 years (n = 23) Male and female participants with chronic heart failure, age range 65–80 years (n = 10) The trial group and control group were exposed to forest and urban environment, respectively, and walked for 1.5 h in the morning and afternoon 1) The trial began in the summer. 2) The trial lasted for 5 days. 3) All groups had the same diet. 4) Smoking, drinking alcohol and caffeinated beverages were prohibited during the trial. 5) Medication taken normally during the trial POMS:
D*#
V↓
T-A#
F↓
C*↓
A-H*↓
BNP*#
N-terminal pro-BNP!
Endothelin-1#
ANGII↓
ANGII receptor type 1↑
ANGII receptor type 2 *↑
Angiotensinogen↓
IL-6#
TNF-α↓
CRP↓
Total superoxide dismutase#
Malondialdehyde#
Yu
(2017) [33]
NRCT (before-after study)※ Male and female participants, age range 45–86 years (n = 128) N/A participants were recruited at the gate of the forest park to conduct a 2-h forest tour and walk a total of 2.5 km 1) The trial began in the summer. 2) Smoking, drinking alcohol and caffeinated beverages were prohibited during the trial POMS:
D*↓
V*↑
T-A*↓
F*↓
C*↓
A-H*↓
STAI score*↓
Pulse rate *↓
SBP *↓
DBP*↓
lnHF↓
lnLF/lnHF↑
Bang (2018) [34] NRCT (before-after study)※ Elementary school students, the average age was 11.83 years (n = 24) Elementary school students, the average age was 11.75 years (n = 28) The trial group allocated 30 min for the lecture and 60 min for the forest activities, while the control group took only indoor classes 1) The trial began in the summer. 2) Once a week for 10 weeks. 3) Children with medical treatment and contraindications to exercise were excluded 1) Trial group
Health status questionnaire:
Perceived health status↑
Rosenberg Self-Esteem Scale:
Self-esteem*↑
Children’s Depression Inventory:
D*↓
Peer relationship instrument:
Peer relationships↓
Conners-Wells Adolescents Self-Report
Scales:
Attention deficit and hyperactivity↑
2) Control group
Health status questionnaire:
Perceived health status↑
Rosenberg Self-Esteem Scale:
Self-esteem↓
Children’s Depression Inventory:
D↓
Peer relationship instrument:
Peer relationships↑
Conners–Wells Adolescents Self-Report
Scales:
Attention deficit and hyperactivity↓
1) Trial group
lnLF/lnHF↑
2) Control group
lnLF/lnHF↓
Bielinis (2018) [35] RCT※ Male (n = 18) and female (n = 13) participants, the average age was 21.45 years Male (n = 18) and female (n = 13) participants, the average age was 21.45 years The trial group was exposed to the forest environment (deciduous broad-leaved forest) and watched the scenery for 15 min, while the control group was exposed to the urban environment and watched the scenery for 15 min 1) The trial began in the winter. 2) No talking with each other during the trial Positive and negative affect schedule:
Positive*#
Negative#
POMS:
D#
V*#
T-A#
F*#
C#
A-H#
Restorative Outcome Scale scores*#
Subjective Vitality Scale scores*#
N/A
Chen (2018) [36] NRCT (before-after study)※ Female participants, age range 36–62 years (n = 16) N/A Day 1, participants were exposed to forest environments for walking. Day 2, participants were exposed to forest environments and made handicrafts 1) The average air temperature during the trial was 13.8 °C. 2) participants had the same accommodation and diet. 3) Smoking and stimulant foods were prohibited during the trial POMS:
D↓
V*↑
T-A*↓
F*↓
C*↓
A-H*↓
STAI scores*↓
Pulse rate↓
SBP*↓
DBP↓
Salivary α-amylase↓
Hassan (2018) [37] RCT (cross-over study) ※ Male and female participants, age range 19–24 years (n = 30) Male and female participants, age range 19–24 years (n = 30) Day 1, the trial group was exposed to forest environment and walked for 15 min, while the control group was exposed to urban environment and walked for 15 min. Day 2, the two groups interchanged environments 1) The average air temperature on the first day was 22 °C, and the average air temperature on the second day was 27 °C. 2) The trial lasted for 2 days. 3) Participants had the same accommodation and diet STAI scores#
SD method:
Comfortable feeling#
Natural feeling#
Relaxed feeling#
SBP#
DBP#
High alpha brain waves#
High beta brain waves#
Relaxation scores#
Attention scores#
Kobayashi (2018) [38] RCT (cross-over study) ※ Male and female participants, age range 19–29 years (n = N/A) Male and female participants, age range 19–29 years (n = N/A) Day 1, the trial group was exposed to forest environment and walked for 15 min, while the control group was exposed to urban environment and walked for 15 min. Day 2, the two groups interchanged environments 1) The trial was carried out in 57 cities and forest areas. 2) The trial lasted for 2 days. 3) The total number of participants was 684, and the numbers of participants from trial group or control group were different in every trial N/A lnHF#
lnLF/lnHF #
Mao
(2018) [39]
RCT※ First trial, male and female participants with chronic heart failure (n = 23).
Second trial, male and female participants with chronic heart failure (n = 10)
Male and female participants with chronic heart failure (n = 10) The trial group was exposed to forest environment, while the control group was exposed to urban environment 1) The trial was carried out twice, the first time in late summer for 5 days, and the second time in early autumn for 5 days. 2) No alcohol or tea was allowed during the trial N/A BNP*#
IL-6!
TNF-α*#
Total superoxide dismutase!
Malondialdehyde#
SBP↓
DBP↓
Song (2018) [40] RCT (cross-over study) ※ Male participants, average age was 21.7 years (n = 6) Male participants, the average age was 21.7 years (n = 6) Day 1, the trial group was exposed to forest environment, while the control group was exposed to urban environment. Day 2, the two groups interchanged environments 1) The trial was conducted in the summer from 2005 to 2013 and lasted for 2 days at a time. 2) The study was conducted in 52 urban and forest areas with a total of 585 participants. 3) Smoking and drinking alcohol were prohibited, and limited caffeine intake POMS:
D#
V#
T-A#
F#
C#
A-H#
N/A
Tsao (2018) [41] NRCT (before-after study)※ Male and female participants, the average age was 60.4 years (n = 11) N/A Participants were exposed to forest environment and walked 1.5 h in the morning and afternoon (in two different forests) 1) The trial began in the winter. 2) The trial lasted for 5 days. 3) The participants had no diabetes, cardiovascular disease or other major diseases. 4) Diet control began 10 days before the trial N/A NK cells↑
NK cells activity*↑
Wang (2018) [42] NRCT (before-after study) ※ Male and female college students (n = 22) N/A The participants carried out a 2 to 3-day forest trip 1) The trial was conducted in the fall of 2015, 2016 and 2017. 2) Participants had the same diet. 3) Smoking, coffee and tea were not allowed during the trial N/A 1) Day after the trial:
Urinary hydrogen peroxide*↓
Urinary 8-hydroxy-2’deoxyguanosine*↓
2) One week after the test:
Urinary hydrogen peroxide*↓
Urinary↓
8-hydroxy-2’deoxyguanosine*↓
Song
(2019) [43]
RCT (cross-over study) ※ Female participants, the average age was 21 years (n = 6) Female participants, the average age was 21 years (n = 6) The participants walked in urban or forest environment for 15 min (about 1 km) 1) The trial was conducted in late summer and early autumn of 2014, 2015 and 2017. 2) The trial was conducted in 6 different urban and forest environments with a total of 72 participants. 3) Smoking, drinking alcohol was prohibited, and limited caffeine intake POMS:
D#
V#
T-A#
F#
C#
A-H#
SD method:
Comfortable feeling#
Natural feeling#
Relaxed feeling#
lnHF#
lnLF/lnHF#
Heart rate#
  1. *Significant intra-group differences
  2. #Significant inter-group differences
  3. n, sample size; “↑”, indicators rise; “↓”, indicators decline; “!”, irregular index; N/A, no report; “※”, has passed ethical review; “+”, illustrates the grouping method; ANGII, Angiotensin II; A-H, anger and hostility; BDI, Beck depression inventory; BNP, Brain natriuretic peptide; C, confusion; Cho, total cholesterol; COPD, chronic obstructive pulmonary disease; CRP, C-reactive protein; D, depression; DBP, diastolic blood pressure; F, fatigue; HRV, heart rate variability; HDL, High density lipoprotein; IL, Interleukin; LDL, low density lipoprotein; lnHF, the natural logarithmic value of the high frequency of heart rate variability; lnLF, the natural logarithmic value of the low frequency of heart rate variability; NK, Nature killer; NKT, Nature killer T; NRCT, non-randomized controlled trial; POMS, profile of mood states; RCT, randomized controlled trial; SBP, systolic blood pressure; SD, semantic differential; STAI, state-trait anxiety inventory; T-A, tension and anxiety; TNF-α, tumor necrosis factor-α; V, vigor; VAS, visual analog scale