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sustainability
Review
Effect of Nature Walks on Depression and Anxiety:
A Systematic Review
Yasuhiro Kotera * , Melinda Lyons, Katia Correa Vione and Briony Norton
Citation: Kotera, Y.; Lyons, M.;
Vione, K.C.; Norton, B. Effect of
Nature Walks on Depression and
Anxiety: A Systematic Review.
Sustainability 2021,13, 4015.
https://doi.org/10.3390/su13074015
Academic Editor: Takahide Kagawa
Received: 5 March 2021
Accepted: 2 April 2021
Published: 4 April 2021
Publisher’s Note: MDPI stays neutral
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Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Human Sciences Research Centre, University of Derby, Derby DE22 1GB, UK; m.lyons@derby.ac.uk (M.L.);
k.vione@derby.ac.uk (K.C.V.); b.norton@derby.ac.uk (B.N.)
*Correspondence: y.kotera@derby.ac.uk
Abstract:
The benefits of nature for our health have been an increasing research focus in recent
years. In the context of a global increase in mental health diagnoses, the potential health benefits
of nature have attracted attention. One practical nature treatment is to walk in nature. However,
evidence for this practice on mental health has not been comprehensively appraised to date. This
systematic review synthesized the effects of nature walks for depression and anxiety, and evaluated
the methodological rigor of studies. Academic databases including ProQuest, PsycINFO, Science
Direct, and Google Scholar were utilized to identify eligible articles, which were examined using the
Newcastle–Ottawa Scale. Of 385 articles initially retrieved, 12 studies met all the eligibility criteria
(nine pre-post within-subject studies, two quasi-experimental studies, and one experimental between-
subjects study). These studies demonstrated that nature walks were effective for state anxiety but not
generalized anxiety and the effects for depression were inconsistent. Findings indicate that nature
walks may be effective for mental health, especially for reducing state anxiety. However, the quality
of the included studies varied, and sample sizes were small, suggesting a need for more rigorous and
large-scale research.
Keywords: nature walk; state anxiety; PRISMA; nature-based intervention; systematic review
1. Introduction
In recent years, there has been increasing interest in the psychological and physiologi-
cal benefits for individuals of spending time in nature [
1
]. Some of this interest is likely
to have been motivated by acknowledging the damage from harmful human activities on
our planet’s fragile ecosystems and a keenness to attempt to reverse the harm [
2
] as well as
from individual experiences of the simple benefits of enjoying time outside [
3
]. Spending
time in nature and feeling connected to nature have positive impacts on people’s mental
health and wellbeing [
1
]. There is evidence that undertaking physical activity in nature
can provide benefits above and beyond the benefits from the physical activity, through an
increased connection to nature. The scope of physical activities examined embraces activi-
ties from the extremes of “free solo” climbing and kayaking [
4
] to less strenuous activities
such as bird-watching or watching nature documentaries on TV [
5
] and the most popular
“middle-ground” activities involving spending time in nature without strenuous activity
including walking in nature. Nature-based interventions are potentially cost-effective
treatments [
6
] that can provide multiple benefits [
7
] and are potentially accessible to a
range of people providing there is adequate provision of public greenspace [
8
]. Forest
bathing (shinrin-yoku) has received particular attention because it is often free and more
accessible than established health interventions [
9
]. Other nature-based interventions,
including walking in nature, have been demonstrated to have positive wellbeing impacts,
including reducing stress levels [
10
]. Likewise, conducting a nature walk in a group re-
duced stress from stressful life events [
11
]. However, as for any therapy, there is still a need
to understand how health benefits manifest before nature-based activities could be utilized
Sustainability 2021,13, 4015. https://doi.org/10.3390/su13074015 https://www.mdpi.com/journal/sustainability
Sustainability 2021,13, 4015 2 of 17
in practice [
12
]. A substantial increase in the research base is required before nature-based
activities can be prescribed alongside established therapies [9].
There is an urgent need for effective and cost-effective treatments for mental health
conditions [
13
]. Mental health is a global and growing health challenge. In 2017, an esti-
mated 792 million people were affected by mental health issues worldwide [
14
]. Since then,
the COVID-19 pandemic and associated widespread socio-economic changes are leading
to a mental health crisis globally [
15
]. Of the conditions assessed in 2017, anxiety and
depression were the most prolific disorders reported, affecting 284 million and 264 million
people, respectively [
14
]. Both of these conditions have increased prevalence during the
COVID-19 pandemic [16,17].
Anxiety encompasses a range of disorders including Generalized Anxiety Disorder,
Panic Disorders, and Social Anxiety Disorders. These disorders can hinder a person’s
ability to function normally, impacting job and academic performance, and personal
relationships [
18
]. During the COVID-19 pandemic, Hamilton and Coates [
19
] surveyed
6430 people in the UK and identified that almost half of the sample reported high anxiety,
with anxiety scores showing a marked increase from pre-pandemic scores. As for many
mental health conditions, anxiety is under-diagnosed, and there is a noted treatment gap for
anxiety globally [
20
]. Even where treatment has been prescribed, it still may not be reliable
or wholly effective. The main pharmacological treatments (most usually SSRIs (selective
serotonin reuptake inhibitors) and SNRIs (serotonin-norepinephrine reuptake inhibitors))
have significant potential for adverse effects and drug-drug interactions [
21
]. Psychological
therapies, such as CBT (Cognitive Behavioral Therapy), are recognized to have good efficacy
but are still most effective when used in combination with pharmacological treatments [
22
].
Considering the long experience of testing and patient use of these medications, there is a
need for different thinking about mental health therapy—perhaps toward a nature-based
treatment approach.
During the COVID-19 pandemic, it was estimated that almost one in five adults expe-
rienced some form of depression, doubling from around one in ten prior to the pandemic
with more than half of adults who experienced some form of depression also report-
ing high levels of anxiety [
23
]. Recognized symptoms include feeling sad or being in
a depressed mood, loss of interest or pleasure in activities once enjoyed, loss of energy,
and feeling worthless or guilty [
24
]. Treatments usually include talking therapies and
medications such as TCAs (tricyclic antidepressants), SSRIs (selective serotonin reuptake
inhibitors), and SNRIs (serotonin-norepinephrine reuptake inhibitors). However, some
of these do not yield the intended improvements. Many of the pharmacological treat-
ments have unpleasant side effects [
25
]. Furthermore, even with the extensive testing and
long history of use of these conventional treatments, patients with depression can both
improve and remit unexpectedly [
26
]. As for anxiety, these challenges suggest a need
to explore new ways of thinking about therapy for depression, such as those offered by
nature-based treatments.
The COVID-19 pandemic placed a heavy burden on health services including mental
health services [
27
]. The main psychological and pharmacological therapies are heavily
reliant on limited and often costly resources, leading to delays in treatment. While some
service providers have responded creatively to the shortfall during the pandemic, for
example, by moving CBT online to sustain the care processes [
28
], it is clear that mental
health systems need further innovation [
29
]. Greater need and reduced availability should
drive attention toward free and publicly accessible therapies that are not reliant on the
availability of professional care processes. This rationalizes a need to consider the efficacy
of nature-based therapies in a specific way.
Here, we systematically reviewed the literature for evidence of the effect of nature
walks on anxiety and depression outcomes. Nature walks are walks on a trail in a natural
setting such as forests, woodlands, or parks [
30
] that can take any time from 15 min [
31
]
to a few hours [
32
]. Nature walks can be undertaken by diverse populations (e.g., cancer
survivors [
32
], university students [
33
]) and conducted in any season of the year [
31
,
34
].
Sustainability 2021,13, 4015 3 of 17
We focused on nature walks as an example of a nature-based therapy because they are
simple and low-risk to undertake and potentially accessible to many people [
35
,
36
]. As
these practical aspects are crucial in the delivery of treatment, the mental health effect of
nature walks was chosen to be evaluated in this review.
2. Materials and Methods
This systematic review followed the preferred reporting items for systematic review
and meta-analysis guidelines (PRISMA [
36
]) to review the literature in an organized
manner and assess the quality of evidence for the psychological effects of nature walks.
Klassen, Jadad, and Moher’s framework [
37
] was used to help maintain the validity of our
findings, considering question, criteria, missing articles, quality of the studies, assessment,
and results. The extended version of the PICO (population, intervention, control, and
outcomes) format [
38
] was created to establish a researchable question by focusing on
four key components [
39
]. The primary research questions for this systematic review are
(i) “How effective are nature walks for depression and anxiety?” and (ii) “What quantity
and quality of evidence has been reported?”
2.1. Literature Search
Following a consultation with a subject librarian [
40
,
41
], four research databases—
ProQuest, PsycINFO, Science Direct, and Google Scholar—were accessed via EBSCO to
conduct a comprehensive literature search, focusing on where, when, who, how, what, and
why [
42
,
43
]. Articles published before 31 October 2020 were considered in this systematic
review. Three hundred and eighty-three articles were retrieved with search terms “nature”
AND “walk” AND “psychology*” (n= 333) as well as “forest” AND “walk” AND “psy-
chology*” (n= 50) in the title and abstract (other words such as “grassland”, “coastal”,
“greenspace”, and “woodland” were searched combined with “walk” AND “psychology*”;
however, only a small number of articles were retrieved, and none were eligible). Addi-
tionally, manual reference searches in published reviews [
43
,
44
] identified two articles [
40
].
Of a total of 385 articles, 44 were duplicates and therefore were removed. Three hundred
and forty-one articles were screened for title and abstract, and 45 articles were reviewed in
full text, which identified 12 articles that met all eligibility criteria (Figure 1). The co-author
Y.K. completed the literature search, which was then reviewed by the co-author K.C.V.
Sustainability 2021, 13, x FOR PEER REVIEW 3 of 20
survivors [32], university students [33]) and conducted in any season of the year [31,34].
We focused on nature walks as an example of a nature-based therapy because they are
simple and low-risk to undertake and potentially accessible to many people [35,36]. As
these practical aspects are crucial in the delivery of treatment, the mental health effect of
nature walks was chosen to be evaluated in this review.
2. Materials and Methods
This systematic review followed the preferred reporting items for systematic review
and meta-analysis guidelines (PRISMA [36]) to review the literature in an organized man-
ner and assess the quality of evidence for the psychological effects of nature walks. Klas-
sen, Jadad, and Moher’s framework [37] was used to help maintain the validity of our
findings, considering question, criteria, missing articles, quality of the studies, assessment,
and results. The extended version of the PICO (population, intervention, control, and out-
comes) format [38] was created to establish a researchable question by focusing on four
key components [39]. The primary research questions for this systematic review are (i)
“How effective are nature walks for depression and anxiety?” and (ii) “What quantity and
quality of evidence has been reported?”
2.1. Literature Search
Following a consultation with a subject librarian [40,41], four research databases—
ProQuest, PsycINFO, Science Direct, and Google Scholar—were accessed via EBSCO to
conduct a comprehensive literature search, focusing on where, when, who, how, what,
and why [42,43]. Articles published before 31 October 2020 were considered in this sys-
tematic review. Three hundred and eighty-three articles were retrieved with search terms
“nature” AND “walk” AND “psychology*” (n = 333) as well as “forest” AND “walk”
AND “psychology*” (n = 50) in the title and abstract (other words such as “grassland”,
“coastal”, “greenspace”, and “woodland” were searched combined with “walk” AND
“psychology*”; however, only a small number of articles were retrieved, and none were
eligible). Additionally, manual reference searches in published reviews [43,44] identified
two articles [40]. Of a total of 385 articles, 44 were duplicates and therefore were removed.
Three hundred and forty-one articles were screened for title and abstract, and 45 articles
were reviewed in full text, which identified 12 articles that met all eligibility criteria (Fig-
ure 1). The co-author Y.K. completed the literature search, which was then reviewed by
the co-author K.C.V.
Figure 1. PRISMA flow diagram of the article selection process.
Figure 1. PRISMA flow diagram of the article selection process.
Sustainability 2021,13, 4015 4 of 17
2.2. Selection of Studies and Outcomes
In order to be further analyzed, articles needed to (a) include a nature walk only,
(b) measure depression and/or anxiety, (c) report an empirical intervention study (i.e.,
pre- and post-intervention scores of depression/anxiety), and (d) be published in a peer-
reviewed academic journal written in the English language. Articles were excluded if they
(a) included other nature-based interventions (e.g., shinrin-yoku), (b) did not measure
either depression or anxiety, (c) used a single-participant design (i.e., case studies), and
(d) did not examine an intervention (e.g., articles that only introduced and/or discussed
concepts or research protocols) (see Table 1).
Table 1. Extended PICO for this review.
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
Population Any population
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
2.3. Data Extraction and Synthesis
The co-author Y.K. conducted all the searches and reviewed all the search results. If
the title and abstract of the article suggested a match with the eligibility criteria, the articles
were shortlisted for further analysis (n= 45). The co-author K.C.V. reviewed the selection
process to minimize any potential bias. After K.C.V.’s review, full texts of the shortlisted
articles were appraised by both co-authors independently, who then discussed and agreed
which articles met the eligibility criteria. No additional eligible articles were identified in
forward and backward reference searches.
Using a data extraction table, developed by Sturt et al. [
45
], key information of in-
cluded studies was presented: publication details (authors, year, and country), study
design and setting, participant characteristics, details of demographic data, intervention
details, outcome measures, and study findings (see Table 2).
2.4. Quality Scoring: Assessing the Risk of Bias
The Newcastle–Ottawa Scale (NOS) was used to appraise the methodological quality
and risk of bias [
46
]. Star marks (0–9) were used to indicate the quality scoring for each
study (high risk: 0–3, medium risk: 4–6, low risk: 7–9) regarding: (a) representativeness
of study group selection (four stars maximum), (b) comparability of groups (two stars
maximum), and (c) ascertainment of either the exposure or outcome of interest (three
stars maximum). Because the NOS was originally designed for medical research, some
adjustments were made in this review focusing on nature walk: (a) the word “exposure”
was changed to “intervention” (e.g., “Ascertainment of intervention”), (b) “Demonstration
that outcome of interest was not present at start of study” to “Demonstration that the
measured outcome was assessed before the intervention”; and (c) a star was given if the
outcome was measured using a validated psychometric scale, instead of medical records,
in the first item of “Outcome” (i.e., “Assessment of Outcome”).
Sustainability 2021,13, 4015 5 of 17
Table 2.
Study details of selected articles exploring the effects of nature walk on depression and anxiety (to be used in Results) (for details on “Nature/Urban exposure” and “Season”, see
Appendix A).
No. Year Author(s) Country Sample and Setting Intervention Details Nature/Urban Exposure Season Measures Findings
1 2020 Lesser et al. [32] 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. [
47
]
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. [48] 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;
forest. Not recorded.
State-Trait Anxiety
Inventory (STAI)
Nature walk reduced
state anxiety.
4 2019 Song et al. [31] 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. [33] 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;
bamboo forest.
One day. Season
not specified. STAI Nature walk reduced
state anxiety.
Sustainability 2021,13, 4015 6 of 17
Table 2. Cont.
No. Year Author(s) Country Sample and Setting Intervention Details Nature/Urban
Exposure Season Measures Findings
6 2018 Song et al. [49] 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.
[50]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;
urban woodland.
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.
[51]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. [52] 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.
Sustainability 2021,13, 4015 7 of 17
Table 2. Cont.
No. Year Author(s) Country Sample and Setting Intervention Details Nature/Urban
Exposure Season Measures Findings
10 2015 Song et al. [53] 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.
[54]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. [55] 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;
city area.
One day.
Late autumn
(November).
POMS and STAI
Nature walk
reduced anxiety
(both POMS and
STAI) but not
depression.
Sustainability 2021,13, 4015 8 of 17
3. Results
3.1. Characteristics of the Studies
Of the 12 included studies, nine were pre-post within-subject studies [
31
–
33
,
48
–
50
,
52
,
53
,
55
], two were quasi-experimental studies [
34
,
54
], and one was an experimental between-
subjects study [
51
]. Study location varied considerably (see Table 2), six studies were
conducted in Asia (China and Japan), three were in North America (USA and Canada) and
in Europe (England, Finland, and Poland). Nine of the studies compared a nature walk
with an urban walk, one compared a nature walk with no walk, and one study included
the assessment of the outcomes in a typical day that did not involve walking in any of
the settings.
Regarding the psychological outcomes, eight of the included studies assessed anxiety
through either the Generalized Anxiety Disorder-7 or the State-Trait Anxiety Inventory;
two studies assessed depression using either the Beck Depression Inventory-II or the Major
Depressive Inventory, and six assessed mood using the Profile of Mood States. Sample sizes
were generally small (<100) for all but the Song et al. [49] and Marselle et al. studies [54].
Overall, the studies demonstrated that nature walks were successful in reducing state
anxiety [
31
–
33
,
48
,
51
,
55
], but the effects on generalized, trait anxiety were mixed [
32
,
49
].
In six studies, a significant reduction in depression was also observed [
31
,
34
,
49
,
50
,
52
,
53
].
However, Janeczko et al. [
47
] reported a reduction in depression regardless of the type of
walking (nature or urban). In fact, the impact of nature walking on depression appears to
be less consistent and was not observed by Song et al. [55].
Regarding the environments where nature walks were undertaken, eight studies were
in a forest or woodland [
31
–
34
,
48
,
49
,
52
,
55
], three studies included more than one type of
nature [
50
,
53
,
54
], and one study was in a predominantly grassland environment [
51
]. There
were water features present near the route in three studies [
48
,
50
,
53
]. Forest types varied
considerably between studies, including a bamboo forest [
33
], deciduous trees [
34
,
55
],
and coniferous forest [
47
], and four studies did not provide enough detail to determine
the type [
32
,
48
–
50
]. Three studies were undertaken in autumn [
34
,
53
,
55
], three were in
spring/summer [
31
,
49
,
50
], one study spanned four seasons but indicated little seasonal
variation in the region [51], one likely varied but was not specified [54], and three did not
specify, although images and descriptions implied trees were in leaf [32,33,48,52].
3.2. Risk of Bias
The risk of bias of the 12 included studies was deemed to be medium to high (see
Table 3). Five studies were deemed medium-risk [
34
,
48
,
50
,
51
,
54
], especially due to a
lack of a control group and for assessing the follow-up immediately after the interven-
tion. In only three of these studies was the representativeness of the sample adequately
addressed [
34
,
48
,
54
]. Bratman et al.’s [
51
] scored particularly well in comparability.
Marselle et al. [
54
] had the largest sample amongst all selected studies (n>1000), but
the experimental group was twice as large as the control group, and the researchers did
not measure the outcome before the intervention.
Finally, seven studies were deemed to have a high risk of bias [
31
–
33
,
49
,
51
,
52
,
55
]. Two
studies conducted a within-subject design with small samples [
33
,
55
]. None of the studies
assessed the outcome before the intervention and only tested the effect immediately after
the intervention, not considering long-term effects.
Sustainability 2021,13, 4015 9 of 17
Table 3. Assessment of risk of bias for intervention studies.
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) [32] * * * 3
Janeczko et al. (2020) [
47
]
* * * * * 5
Koselka et al. (2019) [48] * * * * 4
Song et al. (2019) [31] * * 2
Hassan et al. (2018) [33] * * 2
Song et al. (2018) [49] * * 2
Korpela et al. (2016) [50] * * * * * 5
Bratman et al. (2015) [
51
]
* * * ** * 6
Song et al. (2015) [52] * * 2
Song et al. (2015) [53] * * 2
Marselle et al. (2014) [
54
]
* * * * * 5
Song et al. (2013) [55] * * 2
* (star mark) indicates that the study addressed the assessment item.
4. Discussion
This systematic review examined the quality and extent of evidence in studies in-
vestigating the effects of nature walks on depression and anxiety. Only 12 studies were
identified focusing specifically on an empirical evaluation of this intervention and reported
in English language peer-reviewed journals. Nature walks were found to reduce state
anxiety consistently but not generalized anxiety. There were no clear effects of nature walks
on depression in these studies. The small sample size and large variation in approach to
the studies mean it is not possible to draw conclusions about the type of nature walk that
would be most beneficial or who would benefit most from these.
The health benefits of spending time in nature [
56
–
58
] and of walking [
59
,
60
] are
well established. This review has found there are very few studies focusing specifically
on walking in nature for two specific mental health outcomes: anxiety and depression.
Consistent with studies focused just on walking, the effects on anxiety and depression
reported in studies included in this review were positive or neutral [
61
,
62
]. As reported
in a meta-analysis on forest bathing [
63
], anxiety was the one mental health condition
for which nature walks were consistently reported to be beneficial. More specifically,
the current review identified that nature walks were effective for state anxiety but not
for generalized anxiety. This may be explained by the soothing effects of phytoncides,
Sustainability 2021,13, 4015 10 of 17
antimicrobial organic compounds released from plants [
64
], which are known to reduce
stress and anxiety [
64
]. Indeed, phytoncides were also related to reduced depression
on a self-report measure [
65
]; however, more robust biological evidence supports a link
between phytoncides and anxiety [
66
]. Further research is needed to examine these specific
pathways through which nature walks provide mental health benefits.
A number of reviews looking at the physical and mental health benefits of walking
have identified a lack of consistency in study design and could therefore not draw strong
conclusions about the benefits and most effective interventions [
67
–
69
]. This challenge
is reflected in our review, where studies varied substantially in the participant group
composition and the intervention details. Participant groups included people with pre-
existing physical health conditions (cancer [
32
]), pre-existing mental health conditions
(depression [
50
]), any participant (but health controlled for [
54
]), or primarily healthy
subjects. Variation in participant groups made drawing any conclusions particularly
difficult in relation to depression outcomes, which were examined in only three studies.
Marselle et al. [
54
] found group walks in nature to be a strong predictor of lower depression
symptoms, while two studies focused on individuals found opposite effects of nature
walks on depression symptoms [
34
,
55
]. It is possible that walking in a group was the
important aspect of Marselle et al.’s study [
54
], although Janeczko et al. [
47
] also found
lowered depression symptoms on individual walks, and previous work has similarly
found inconclusive results of the benefits of group over individual activity [
61
]. A previous
systematic review has found walking to reduce depression symptoms [
61
] and that exercise
more generally is important in reducing depression symptoms [
70
,
71
], and it may be that
the act of walking rather than the environment the walk is in is what is important for
depression. There is insufficient evidence from the studies included in this review to draw
a robust conclusion.
The details of the intervention varied between studies. Lesser et al. [
32
] involved
walks up notable slopes, while two studies noted the route was flat [
33
,
51
]. Walk duration
varied from 2.5 h a week over multiple weeks [
32
] through to a single, 15-min route [
33
,
55
].
Janeczko et al. [
47
] found walking duration to have an important effect on all outcomes,
indicating these interventions are not comparable. The appropriate time “dose” of walking
is not well understood [
62
], and our review suggests the methodological approach needs
to be strengthened in future studies. This information is available for exercise more
generally [
70
], and methodological approaches could be extrapolated to the nature walk
context. None of the studies in this review compared walking to other treatment approaches
(pharmacological treatments or psychological therapies) although previous work has
suggested that treatment of depression with exercise may be most effective when combined
with a pharmacological approach [
68
]. Another aspect of the studies related to time is
the duration of effect. None of these studies assessed long-term effects of any of the
interventions, although one did indicate the study was a pilot, and the intention was to
follow up with a longitudinal study [48], which would be a welcome addition.
A key benefit identified for nature-based therapies is that they are free and publicly
accessible, in principle. Nature is not equally accessible to everyone, however [
72
], and
even where some form of nature is available it is not always of the same “quality” [
73
]. In
working toward recommendations for nature-based health interventions, it is important
to understand what nature is most beneficial to address both equity of provision and
to consider health outcomes in the context of other functions and benefits provided by
both greenspace [
74
] and blue space [
75
]. It was not possible in this study to look for
effects of particular types of natural environment as the environment varied considerably
between studies, from the broad vegetation type (e.g., forest vs. grassland), the inclusion
of additional features (e.g., water), and the season of study (autumn vs. spring/summer)
(Appendix A). There is a growing body of literature suggesting that people’s response to
nature varies depending on very specific measures of the environment, including vegetation
structure [
76
,
77
], leaf color and shape [
78
], season [
79
], perceived biodiversity [
80
,
81
], and
infrastructure on and management of the site [
82
]. Within the included studies, only
Sustainability 2021,13, 4015 11 of 17
one directly controlled for different aspects of the environment in their site selection [
47
],
and only a subset measured additional features of the environment [
33
,
34
,
55
]. In most
of the reviewed studies, it is not possible to separate out the influence of the different
aspects of the environmental conditions in the walking environments that may have
been providing any benefit. For example, two studies compared a nature walk with a
walk by a busy road [
51
,
55
]. These two environments differ on a wide range of metrics
including temperature, humidity (measured in Song et al. [
55
], Hassan et al. [
33
], and
Janeczko et al. [
47
]), light levels (measured in Song et al. [
55
]), noise pollution (measured
in Janeczko et al. [
47
]), air pollution, physical disturbances (e.g., passing cars), colors,
and shapes of the visual landscape. To parse out the relative importance of these features,
studies testing the different elements of the environment would be beneficial. Future studies
addressing the types of vegetation, vegetation context (including associated infrastructure),
the season, and the levels of biodiversity most beneficial for achieving health benefits from
nature walks would be important contributions to the literature [74,80,83].
As outlined above, the studies included in this review were not sufficiently comparable
in study design, participant selection, or intervention approach to draw robust conclusions
about the benefits of nature walks as an intervention for anxiety or depression. The
consistently positive effect of nature walks on state anxiety measures combined with the
medium to high risk of bias in the majority of studies included in this review suggest a
need for more targeted research in order to develop recommendations for health practice.
Despite the small number of studies, three continents were included (Asia, North America,
and Europe). Variation in effect between continents, country, and climatic region is an area
where future research would be beneficial. Consistent patterns across regions could be
sought by focusing on the environmental conditions and specific measures of the natural
environment (as above). None of the studies were randomized controlled trials. One study
did blind the participants to the purpose of the study. The mental health benefit of walking
in nature is a growing area of research and is reflected in the publication dates of the studies
included in this review, six of which were published in the last four years and all published
within the last nine years. There is a great deal of scope for undertaking more controlled
studies on this intervention for this area to continue to develop.
This review had four primary limitations. The first is that only studies published
in English-language academic journals were included. The number of studies missed
because of this is not known. The second is focusing on articles that are studying walks
exclusively. This strengthens the conclusions as the results can be confirmed to focus
on walks, but studies that report outcomes of nature walks in conjunction or addition
to other interventions may have been missed (e.g., studies that combined walking and
viewing [
84
]). The third limitation is in the specific aims of the included studies. While
the broad goal of all studies was to look at the effects of a nature or forest walk, the
variation in how these were measured reflects differences in the specific aims. Nine of
the studies focused on comparing the relative effects of a nature walk in contrast to an
urban walk [
31
,
34
,
45
,
47
–
49
,
52
,
53
,
55
], two studies compared measures before and after a
walk [
32
,
50
] and one study compared walking to not walking [
54
]. As the literature on
this topic grows, teasing apart these different comparisons would be worthwhile. Lastly,
this study did not focus on “park walks”, as the richness of nature can be significantly
limited in some parks: indeed, some of the included nature walk studies in this review were
conducted in the park; however, the richness of nature was reported. Close examination of
park walk literature can offer additional insights.
5. Conclusions
The 12 studies identified through this review focused specifically on the effects of
nature walks on anxiety and depression and suggest that state anxiety can be reduced
through nature walks. The effect of nature walks on generalized anxiety was mixed. The
evidence for effects of nature walks on depression symptoms was inconclusive. The low
number of studies with high variability in the subjects and the type of nature subjects were
Sustainability 2021,13, 4015 12 of 17
exposed to in these studies suggest more work is required. Given the global challenges to
healthcare systems of anxiety and depression and the relatively cost-effective treatment
intervention of a walk in nature, the establishment of a more robust research base on this
topic is warranted.
Author Contributions:
Conceptualization, Y.K.; methodology, Y.K.; validation, Y.K., M.L., K.C.V.,
and B.N.; formal analysis, K.C.V.; investigation, K.C.V. and B.N.; data curation, K.C.V. and B.N.;
writing—original draft preparation, Y.K., M.L., K.C.V., and B.N.; writing—review and editing, Y.K.,
M.L., K.C.V., and B.N. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not Applicable.
Informed Consent Statement: Not Applicable.
Data Availability Statement:
No new data were created or analyzed in this study. Data sharing is
not applicable to this article.
Conflicts of Interest: The authors declare no conflict of interest.
Appendix A
Table A1.
Selected articles exploring the effects of nature walk on depression and anxiety with study details. Full study
details are in Table 2of the main text. Here, “Location” is added, and “Nature/Urban exposure” and “Season” are expanded
to include more detail from the papers.
No. Year Author(s) Country Location Nature/Urban Exposure Season
1 2020 Lesser et al. [32] Canada
Participants from
Fraser Valley, British
Columbia, Canada
“Lush green old growth forest”.
Sloped.
Not recorded. Description
suggests trees are in leaf.
2 2020 Janeczko et al.
[47]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.
One day.
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.
Sustainability 2021,13, 4015 13 of 17
Table A1. Cont.
No. Year Author(s) Country Location Nature/Urban Exposure Season
3 2019 Koselka et al. [48] 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. [31] 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
(ginkgo))
Summer (5 August to
6 September). Variable
conditions. Also recorded:
weather, temperature,
humidity, and illuminance.
5 2018 Hassan et al. [33] China Chengdu
Urban area “that included many
traditional buildings”.
“Well-managed” bamboo forest
Sample photos included.
Flat.
One day.
Season not specified.
Temperature: 22 ◦C in the
bamboo forest; 27 ◦C in the
urban site.
Humidity also recorded.
6 2018 Song et al. [49] 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. [50]
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 19200s sight-seeing tower”.
Both within three km of the city center.
Recruitment in spring.
8 2015 Bratman et al.
[51]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.
Not raining.
Sustainability 2021,13, 4015 14 of 17
Table A1. Cont.
No. Year Author(s) Country Location Nature/Urban Exposure Season
9 2015 Song et al. [52] 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. [53] 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.
[54]
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. [55] Japan Chiba
Urban park. Kashiwanoha Park. Treed.
City area.
Images provided.
One day.
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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