2. Materials and Methods
2.1. Literature Search
2.2. Selection of Studies and Outcomes
2.3. Data Extraction and Synthesis
2.4. Quality Scoring: Assessing the Risk of Bias
3.1. Characteristics of the Studies
3.2. Risk of Bias
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
|1||2020||Lesser et al. ||Canada||Participants from Fraser Valley, British Columbia, Canada||“Lush green old growth forest”.|
|Not recorded. Description suggests trees are in leaf.|
|2||2020||Janeczko et al. ||Poland||Warsaw||Urban: A1 “among single-family buildings with lots of greenery”, “noticeably higher level of noise, the presence of a wide two-lane street, dominating apartment blocks and a smaller share of green space”, green ratio = 12.62%; A2 “multi-family buildings dominated and the share of greenery was smaller”, “a quiet community with detached houses and green areas”, green ratio = 10.5%.|
Forest: B1: Kabaty Forest coniferous forest, “species composition is dominated by pines accompanied by oaks and a share of younger birches and a multitude of limes”, green ratio = 0.58%; B2: Sobieski Forest, deciduous forest, “dominated by broadleaved species, with an old forest, 120–160 years old, and numerous types of trees, such as oaks, pines, and beeches”, green ratio = 0.0%.
Sample photos and aerial images included.
Late autumn (November). Outdoor temperature 10 a.m. 9.2 °C at 10 a.m. in urban areas, 8 °C in the forest. Also recorded: pressure, wind speed, humidity, sound, and light.
|3||2019||Koselka et al. ||USA||Evanston, IL||Both started “parking lot of Harms Woods (George F. Nixon Woods”|
Busy road “crossed Harms Road… and walked east, on the sidewalk of Old Orchard Road. This road is a busy 4 lane road that passes over Interstate 94 as it approaches a large shopping mall approximately 1 km away”.
Forest preserve. “Participants assigned to walk in the forest walked north from the parking lot on a well-groomed gravel trail into the woods along the North Branch Trail…, which follows the Chicago River…. After walking north for approximately 500 m, they crossed a footbridge over the river then walked south on the graveled trail for approximately 750 m…. Distances walked along both routes varied depending on each participants’ pace.”
Sample photos included.
|Photos indicate trees are in leaf.|
|4||2019||Song et al. ||Japan||Six locations: Iwate, Gifu, Hyogo, Ibaraki, and Kanagawa (2 locations)||Each location had one city site, one forest site. |
Forests: Iwate (secondary forest (red
pine and oak) and
artificial forest (larch)); Motosu (secondary forest (oak
and cherry)); Hyogo (secondary forest (oak
and maple)); Ibaraki (secondary forest (red
pine and oak)); Kanagawa 1 (secondary forest (red
pine and oak)); Kanagawa 2 (secondary forest (oak)
and artificial planting
|Summer (5 August to 6 September). Variable conditions. Also recorded: weather, temperature, humidity, and illuminance.|
|5||2018||Hassan et al. ||China||Chengdu||Urban area “that included many traditional buildings”.|
“Well-managed” bamboo forest
Sample photos included.
Season not specified. Temperature: 22 °C in the bamboo forest; 27 °C in the urban site.
Humidity also recorded.
|6||2018||Song et al. ||Japan||52 locations all over Japan (map provided)||City areas were either downtown or near a train station; “safe, well-maintained” forest areas, representative of the region.||Summer.|
|7||2016||Korpela et al. ||Finland||Tampere||Park area: “a lakeside arboretum with flowerbeds, bushes and old trees surrounding a nineteenth-century former manor house”.|
Urban woodland: “area with old trees and views over the lake is on a ridge with a 1920′s sight-seeing tower”.
Both within three km of the city center.
|Recruitment in spring.|
|8||2015||Bratman et al. ||USA||San Francisco Bay Area||Urban walk: “a main thoroughfare through Palo Alto, a busy street with three-to four lanes in each direction and a steady stream of traffic (El Camino Real)”.|
Nature walk: “a park near Stanford University (known as “The Dish”) along a paved path through grassland with scattered shrubs and oak trees”.
Both on “fairly level ground”.
Sample photos included.
|Equal spread across autumn, winter, spring, and summer. Little climatic variation between seasons due to location. Season not analyzed.|
|9||2015||Song et al. ||Japan||Nagano||City; coniferous forest with Japanese cypress trees (Akasawa Shizen Kyuyourin; Akasawa natural recreation forest). Image provided.||Not recorded. Average temperature: forest was 21.4 ± 1.2 °C, urban was 28.1 ± 1.1 °C. Humidity also recorded.|
|10||2015||Song et al. ||Japan||Chiba||Park (Kashiwa-no-ha Park) that contained many hardwood trees (e.g., maple, tulip trees, cherry trees, and chestnut) and a large|
pond; urban residential area.
|Autumn (7, 15, 16 October). Variable weather. Temperature: park 18.0 ± 1.7; city 19.2 ± 1.9.|
Humidity and illumination also recorded.
|11||2014||Marselle et al. ||England||Whole country.||Nature: “natural and semi-natural places, green corridor, farmland, urban green space, coastal, or a mixture of any of the above”.||Not recorded.|
|12||2013||Song et al. ||Japan||Chiba||Urban park. Kashiwanoha Park. Treed.|
Late autumn (November). “Trees in the park had either lost their leaves or the leaves had turned red or yellow”.
Sunny. Temperature: 14.0 °C in the city, 13.8 °C in the park.
Humidity and intensity of illumination also reported.
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|Review Questions||(i) How Effective Are Nature Walks for Depression and Anxiety? |
(ii) What Quantity and Quality of Evidence Has Been Reported?
|Inclusion Criteria||Exclusion Criteria|
|Intervention||Nature walk only||Involving other nature-based interventions (e.g., shinrin-yoku)|
|Comparator||Any comparator including non-comparator|
|Outcomes||Depression and anxiety||Other outcomes|
|Study Design||Empirical intervention studies||Single case studies, cross-sectional studies, qualitative studies, reviews, discussion articles, articles introducing theories/concepts/models/applications|
|Other||Published in a peer-reviewed academic journal in English|
|No.||Year||Author(s)||Country||Sample and Setting||Intervention Details||Nature/Urban Exposure||Season||Measures||Findings|
|1||2020||Lesser et al. ||Canada||9 adult cancer survivors (8 females and 1 male).||2 trail walks per week (2.5 h a week) for 8 weeks with a hiking guide.||Forest—sloped area.||Not recorded.||Generalized Anxiety Disorder-7 and Visual Analog Scale||Significant reduction in state anxiety but not in generalized anxiety.|
|2||2020||Janeczko et al. ||Poland||75 university students (nonclinical) divided into either taking a walk in apartment suburbs; green suburbs; coniferous forest; or deciduous forest.||2-km walk (30 min) keeping distance to each other, not allowed to talk.||Urban: A1: single-family dwellings with more greenery. A2: multi-family buildings with less greenery.|
Forest: B1: coniferous forest; B2: deciduous forest.
|One day. Late autumn (November).||Profile of Mood States (POMS)||Depression was reduced in all groups from pre- to post-walk. No difference was found among groups.|
|3||2019||Koselka et al. ||USA||38 participants (age range 18–35; 22.9 + 4.6 years; 20 females and 18 males; nonclinical) divided into (i) 50-min nature walk, (ii) 50-min walk on busy road, and (iii) activity of daily living. Crossover design.||50-min walk at moderate-intense pace with 9 days of washout period.||Busy road;|
|Not recorded.||State-Trait Anxiety Inventory (STAI)||Nature walk reduced state anxiety.|
|4||2019||Song et al. ||Japan||12 female university students (age of the approaches sample (n = 60) was 21.0 ± 1.3 years) walked for 15 min either in a forest or urban environment.||15-min nature walk and urban walk crossover next day.||Six locations, with a paired city and secondary forest site (mixed oak woodlands).||Summer.||POMS and STAI||Nature walk reduced depression and anxiety, and state anxiety significantly more than urban walk.|
|5||2018||Hassan et al. ||China||60 nonclinical university students (30 females and 30 males; mean age, 19.6 ± 1.42 years) randomly allocated to a 15-min nature or urban walk.||15-min nature walk and urban walk crossover next day.||Urban area; |
|One day. Season not specified.||STAI||Nature walk reduced state anxiety.|
|6||2018||Song et al. ||Japan||585 Japanese male students (Age 21.7 ± 1.6 years) walked for 15 min either in a forest or urban environment. Crossover next day.||15-min nature walk and urban walk crossover next day.||City areas were either downtown or near a train station; “Safe, well-maintained” forest areas.||Summer.||POMS and STAI||Nature walk reduced depression and anxiety, and trait anxiety significantly more than urban walk.|
|7||2016||Korpela et al. ||Finland||13 depression patients (9 females and 4 males; age range 29–59 years, M = 48, Md = 52 years).||2-h walk a week for 8 weeks||Park with a lake and ornamental plantings;|
|Recruitment in spring.||Beck Depression Inventory||Depression reduced from pre- to post-walk, and post-walk to 3-month follow-up.|
|8||2015||Bratman et al. ||USA||60 nonclinical adults (33 females and 27 males, total mean age = 22.9 years) randomly assigned to nature or urban individual walk for 50 min.||Participants were told to take good pictures to blind the intervention. Nature group comprised 30 participants (18 females and 12 males, total mean age = 22.8), and urban group also comprised 30 participants (15 females and 15 males, total mean age = 22.9).||Urban walk: adjacent to a major road.|
Nature walk: grassland, scattered shrub, and oak trees.
|Equal spread across autumn, winter, spring, and summer.||STAI||Nature walk reduced anxiety, relative to urban walk (separate data on state and trait anxiety were not reported).|
|9||2015||Song et al. ||Japan||20 middle-aged hypertensive individuals (58.0 ± 10.6 years) walked for 17 min either in a forest or urban environment. Crossover next day.||17-min nature walk and urban walk crossover next day.||City; coniferous forest.||Not recorded (however, the average temperature of the forest was 24 °C and urban was 28 °C).||POMS||Nature walk reduced depression and anxiety significantly more than urban walk.|
|10||2015||Song et al. ||Japan||23 male university students (age 22.3 ± 1.2 years) walked for 15 min either in a forest or urban environment. Crossover next day.||15-min nature walk and urban walk crossover next day.||Park that contained many hardwood trees and a large pond; urban residential area.||Autumn (October)||POMS and STAI||Nature walk reduced depression and anxiety significantly more than urban walk.|
|11||2014||Marselle et al. ||England||1516 participants (66% were female, and 88% were aged 55 years or older) who had attended at least one session in the Walk for Health (WfH) program responded to online survey.||WfH attendee who continued to walk during the 13-month of the research period was defined as Nature Group Walker, and those who did not as Non-Group Walker. 1081 Nature Group Walkers and 435 Non-Group Walkers were identified.||Nature: “natural and semi-natural places, green corridor, farmland, urban green space, coastal, or a mixture of any of the above”.||Not recorded.||10-item Major Depressive Inventory||Group nature walk reduced depression from T1 to T2.|
|12||2013||Song et al. ||Japan||13 male university students (nonclinical) aged 22.5 ± 3.1 years divided into park walk and city walk. Crossover design.||15-min walk in urban parks and city||Urban park—treed; |
Late autumn (November).
|POMS and STAI||Nature walk reduced anxiety (both POMS and STAI) but not depression.|
|Bias Category||Selection||Comparability||Outcome||Number of Stars (0–9)|
|Author (Year)||Representativeness of Exposed Cohort||Selection of Non-Exposed Cohort||Ascertainment of Intervention||Demonstrate Outcome Assessed before Intervention||Comparability of Cohorts on Basis of Design (*) or Analysis (*)||Assessment of Outcome||Follow-Up Long Enough||Adequacy of Follow-Up|
|Lesser et al. (2020) ||*||*||*||3|
|Janeczko et al. (2020) ||*||*||*||*||*||5|
|Koselka et al. (2019) ||*||*||*||*||4|
|Song et al. (2019) ||*||*||2|
|Hassan et al. (2018) ||*||*||2|
|Song et al. (2018) ||*||*||2|
|Korpela et al. (2016) ||*||*||*||*||*||5|
|Bratman et al. (2015) ||*||*||*||**||*||6|
|Song et al. (2015) ||*||*||2|
|Song et al. (2015) ||*||*||2|
|Marselle et al. (2014) ||*||*||*||*||*||5|
|Song et al. (2013) ||*||*||2|
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