Table 2.
Summary of studies included in the systematic review (k = 13).
| Authors (Years) |
Study Design | Participants (n) | Intervention | Control | Outcome (Measurements) | |
|---|---|---|---|---|---|---|
| 1 | Li et al. (2007) [18] |
One group pre-posttest design | Healthy male, aged 37~55 years (12) Mean age: 43.1 ± 6.1 |
A three-day/two-night trip First day: walked for two hours in the afternoon in a forest field Second day: walked for two hours each in the morning and afternoon in two different forest field On day 3: finished the trip |
None | · NK cells **↑, NK activity **↑, · T cells · granulysin **↑, perforin **↑, granzymes A **↑/B **↑ · WBC, (Lymphocytes *↑, Monocytes*↑, Granulocytes **↓) · T-A *↓, D *↓, A-H, F, C, V **↑(POMS) · the hours of sleep |
| 2 | Li et al. (2008) [19] |
One group pre-posttest design | Healthy female nurses, aged 25~43 years (13) Mean age: 28.8 ± 4.6 |
A three-day/two-night trip First day: walked for two hours in the afternoon in a forest field Second day: walked for two hours each in the morning and afternoon in two different forest field On day 3: finished the trip |
None | · NK cells **↑, NK activity **↑ · T cells *↓ · granulysin **↑, perforin **↑, granzymes A **↑/B **↑ · Adrenalin **↓, noradrenaline (Urine) **↓ · Estradiol, progesterone · T-A, D **↓, A-H, F, C, V (POMS) |
| 3 | Li et al. (2008) [20] |
None-equivalent control group pre-posttest design | Healthy male, aged 35~56 years (E:12, C:11) Mean age: 45.1 ± 6.7 |
A three-day/two-night forest bathing program First day: walked for two hours in the afternoon in a forest field Second day: walked for two hours each in the morning and afternoon in two different forest field On day 3: finished the trip |
A three-day/two-night city trip First day: walked for two hours in the afternoon in an old-style district in the city Second day: walked for two hours around baseball Dome in the morning and 2 h around/in airport in the afternoon On day 3: finished the trip |
· NK cells *↑, NK activity *↑ · T cells · granulysin **↑, perforin **↑, and granzymes A **↑/B **↑ · WBC · Adrenaline (Urine) *↓ |
| 4 | Mao et al. (2012) [21] |
RCT | Healthy male university students (E:10, C:10) Mean age: 20.79 ± 0.54 |
two-night trip walked for 1.5 h each in the morning and afternoon in a forest field |
walked for 1.5 h each in the morning and afternoon in a city site | · NK cells · T cell, B cell *↑, T-helper cells. suppressor cells, natural killer cells · IL-6*↓, TNF-α *↓ · T-SOD, MDA **↓ · ET-1 **↓, Platelet activation · Cortisol *↓, Testosterone · T-A *↓, D *↓, A-H *↓, F *↓, C, V *↑(POMS) |
| 5 | Nakau et al. (2013) [22] |
One group pre-posttest design | Breast cancer or lung cancer (22) Mean age: 58.1 ± 10.8 |
Walking in the forest, Horticultural therapy, yoga meditation, and support group therapy, and sessions were conducted once a week for 12 weeks | None | · NK activity **↑ · Well-being of functional and spiritual (FACIT-Sp): GP, GS, GE, GF *↑, Sp *↑ · Quality of life (SF-36): PF *↑, RP *↑, BP, GH *↑, VT **↑, SF, RE *↑, MH *↑ · Fatigue (CFS) **↓ · T-A *↓, D, A-H, F, C **↓, V (POMS) · STAI: State anxiety **↓, Trait anxiety *↓ |
| 6 | Jung et al. (2015) [27] |
None-equivalent control group pre-posttest design | Workers in the healthcare and counseling service industries (E:19, C:20) Mean age E: 29.42 ± 8.92, C:36.45 ± 12.23 |
3 days, 2 nights, Walking and meditation in the forest, and exposure to a psychological program using music and cognitive-behavioral therapy. | frequently use the environment without participating in the program | · NK activity · Cortisol *↑ · HRV · MBI-GS **↓, WRSI *↓, REQ **↑ |
| 7 | Kim et al. (2015) [28] |
One group pre-posttest design | Stage 3 Breast cancer patient, aged 25~60 years (11) Mean age: 56 ± 5.12 (11) |
Stay in the forest for 14 days, Forest therapy program (Walk, forest life) | None | · NK cells **↑ · Perforin *↑, Granzyme B *↑ |
| 8 | Jia et al. (2016) [29] |
RCT | elderly patients with chronic obstructive pulmonary disease (E: 10, C: 8) Mean age E: 70.1 C: 70 |
4 days, walking in the forest (total 3 h walk/day) | 4 days, walking in the city (total 3 h walk/day) | · NK cells, NKT-like cell, CD8+ T cells · Perforin **↓, Granzyme B · IL-6 *↓, IL-8 **↓, interleukin-1β *↓, TNF-α interferon-γ *↓, CRP *↓ · Cortisol *↓, Epinephrine *↓ · RARC/CCL-18 **↓, TIMP-1 *↓, SP-D *↓ · T-A **↓, D *↓, A-H *↓, F, C, V (POMS) |
| 9 | Han et al. (2016) [30] |
None-equivalent control group pre-posttest design | Full-time employees with chronic widespread pain for more than three months, aged 25~49 years (E: 33, C: 28) Mean age E: 41.6 ± 6.5, C: 37.5 ± 8.4 |
2 days forest therapy program Walking and therapeutic activities in the forest activities (music therapy, psycho-education: coping with pain and stress, bodily exercises, mindfulness-based meditation) |
The control group was instructed not to conduct either heavy loads of domestic or occupational work during the enrollment in this study. | · NK activity **↑ · Heart rate variability (HRV) **↑ · Self-reported pain **↓ (VAS) · Depression **↓ (BDI) · Health-related quality of life **↑ (EQ-VAS) |
| 10 | Mao et al. (2017) [31] |
RCT | Elderly patients with chronic heart failure, Aged from 65 to 80 years (E: 23, C: 10) Mean age 73.86 ± 5.85 years old |
4 days, Walking in the forest (total 3 h walk/day) | 4 days, Walking in the city (total 3 h walk/day) | · IL-6 *↓, TNF-α, CRP · BNP **↓, N-terminal pro BNP · ET-1 **↓, Renin, AGT, Ang II, AT1, AT2 **↑ · T-SOD *↑, MDA *↓ · T-A *↓, D **↓, A-H **↓, F, C **↓, V (POMS) |
| 11 | Lee et al. (2017) [32] |
None-equivalent control group pre-posttest design | Women in their 50 s (E: 9, C: 9) Mean age E: 53.9 ± 2.69, C: 55.5 ± 1.84 |
Forest walking exercise for 12 weeks (3 times/week, 110 min/day) | Ground walking exercise for 12 weeks (3 times/week, 110 min/day) | · NK cells *↑ · Melatonin *↑ |
| 12 | Tsao et al. (2018) [33] |
One group pre-post test design | Middle-aged subjects (11) Mean age: 60.4 |
A five-day/four-night trip (maintain dietary control and walking exercise) First day: walked for 1.5 h in the afternoon in a forest field Next three days: walked for 1.5 h each in the morning and afternoon in two different forest field Fifth day: finished the trip |
None | · NK cells, NK activity **↑ |
| 13 | Lyu et al. (2019) [34] |
None-equivalent control group pre-posttest design | Male College Students (E: 45, C: 15) Mean age E: 20.9 ± 0.24, C: 21.3 ± 0.45 |
Bamboo forest site exposure for three days | City site exposure for three days | · NK cells *↑. NK activity *↑, · granulysin, perforin *↑, granzymes A *↑/B *↑, · corticosterone *↓ · SBP *↓, DBP, HR, SpO2 · T-A *↓, D *↓, A-H *↓, F *↓, C *↓, V *↑ (POMS) |
*: p < 0.05; **: p < 0.01; ↑: indicators rise; ↓: indicators decline; E = Experimental group; C = Control group; POMS = Profile of mood states; T-A = Tension-anxiety; D = Depression: A-H = Anger-hostility,; F = fatigue; C = Confusion; V = Vigor; WBC = hite blood cell; IL-6 = Interleukin-6; TNF-α = Tumor necrosis factors α; T-SOD = Total superoxide dismutase; MDA = Activity and malondialdehyde; ET-1 = Endothelin-1; FACIT-Sp = Functional assessment of chronic illness therapy-spiritual; GP = Physical well-being; GS = Social/family well-being; GE = Emotional well-being; GF = Functional well-being; Sp = Spiritual well-being; CFS = Cancer fatigue scale; SF-36 = 36-Item short-form health survey; PF = Physical functioning; RP = Role-physica; BP = Bodily pain; GH = General health perception; VT = Vitality; SF = social functioning; RE = Role emotional; MH = Mental health; STAI = State-trait anxiety inventory; HRV = Heart rate variability; MBI-GS = Maslach Burnout Inventory-General Survey; WRSI = Worker’s Stress Response Inventory; REQ = Recovery Experience Questionnaire; CRP = C-peptide protein; RARC/CCL-18= Pulmonary and activation-regulated chemokine, TIMP-1= Tissue inhibitor of metalloproteinase-1; SP-D = Surfactant protein D; VAS: Visual analog scale; BDI = Beck Depression Inventory; EQ-VAS= EuroQol Visual Analog Scale; BNP = Brain natriureti; AGT = Angiotensinogen; Ang II = Angiotensin II; AT1 = Angiotensin II type 1 receptor; AT2 = Angiotensin II type 2 receptor; SBP = Systolic blood pressure; DBP = Diastolic blood pressure; HR = Heart rate.