Journal of Affective Disorders 318 (2022) 291–298

Contents lists available at ScienceDirect

Journal of Affective Disorders
journal homepage: www.elsevier.com/locate/jad

The effects of walking in nature on negative and positive affect in adultpsychiatric outpatients with major depressive disorder: A
randomized-controlled study
Kia Watkins-Martin a, Despina Bolanis a, Stéphane Richard-Devantoy b, c,Marie-Hélène Pennestri a, d, Catherine Malboeuf-Hurtubise e, Frederick Philippe f,
Julie Guindon b, Jean-Philippe Gouin g, Isabelle Ouellet-Morin h, i, Marie-Claude Geoffroy a, b, *a

Department of Educational and Counselling Psychology, McGill University, Montreal, QC, Canada
Department of Psychiatry, McGill University, Montreal, QC, CanadacDepartment of Psychiatry, Saint-Jérôme Hospital, Saint-Jérôme, QC, CanadadHôpital en santé mentale Rivière-des-Prairies (CIUSSS-NIM), Montreal, QC, CanadaeDepartment of Psychology, Bishop’s University, Sherbrooke, QC, CanadafDepartment of Psychology, Université du Québec à Montréal, Montreal, QC, CanadagDepartment of Psychology, Concordia University, Montreal, QC, CanadahSchool of Criminology, University of Montreal, Montreal, QC, CanadaiResearch Center of the Montreal Mental Health University Institute, Montreal, QC, Canadab

A R T I C L E I N F O

A B S T R A C T

Keywords:
Major depressive disorder (MDD)
Depression
NatureGreenspace
AffectRandomized-control trial
Physical activity

Background: While walking in nature has been shown to improve affect in adults from the community to a greater
extent than walking in urban settings, it is unknown whether such benefits apply to individuals suffering fromdepression. Using a parallel group design, this randomized controlled trial examined the effects of a single walkin nature versus urban settings on negative and positive affect in adult psychiatric outpatients diagnosed withmajor depressive disorder (MDD).
Method: Participants recruited from a psychiatric outpatient clinic for adults with MDD were randomly assigned
to a nature or urban walk condition. Thirty-seven adults (mean age = 49 years) completed a single 60-minutewalk. Negative and positive affect were assessed using The Positive and Negative Affect Schedule or PANAS
at 6 time points: before the walk, halfway during the walk, immediately post-walk, at home before bedtime, 24 hpost-walk, and 48 h post-walk.
Results: Controlling for baseline levels of affect before the walk, individuals who walked in nature experienced
overall lower levels of negative affect, F(1, 35.039) = 4.239, p = .047, compared to those who walked in urban
settings. Positive affect did not differ across walk conditions.
Limitations: The generalizability of results are limited by the small sample size and the presence of more female
than male participants.
Conclusions: Walking in nature might be a useful strategy to improve negative affect in adults with MDD. Future
research should investigate different ways to integrate the beneficial effects of nature exposure into existingtreatment plans for psychiatric outpatients with MDD.

1. Introduction
Depression is a leading cause of disability and one of the mostcommon mental disorders, affecting over 300 million people worldwide(Friedrich, 2017; Vos et al., 2015; World Health Organization, 2017).

While psychotherapy, pharmacotherapy, or a combination of both are
effective in reducing depressive symptoms (Cuijpers, 2014; Kamenov
et al., 2017), there remains a need for free, complementary strategies
that can be easily implemented by individuals without professional
assistance (Ravindran et al., 2016).

* Corresponding author at: Department of Educational and Counselling Psychology, McGill University, Montreal, Quebec H3A 1Y2, Canada.
E-mail address: marie-claude.geoffroy@mcgill.ca (M.-C. Geoffroy).
https://doi.org/10.1016/j.jad.2022.08.121
Received 23 November 2021; Received in revised form 5 August 2022; Accepted 28 August 2022
Available online 1 September 2022
0165-0327/© 2022 Elsevier B.V. All rights reserved.

K. Watkins-Martin et al.

Journal of Affective Disorders 318 (2022) 291–298

In recent years, there has been a growing interest in the benefits ofspending time in nature for mental health (Bowler et al., 2010; Bragg
and Atkins, 2016; Bratman et al., 2021; Britton et al., 2020; Frumkin
et al., 2017; Hartig and Kahn, 2016; Keniger et al., 2013; Kondo et al.,2018; White et al., 2017), including the alleviation of depression
symptoms (Bratman et al., 2019; Sarkar et al., 2018; White et al., 2021).
One practical way to spend time in nature is to walk, a free and highly
accessible form of physical activity that most people find enjoyable.
Within the general population, a growing number of studies have re­ported that walking in nature confers greater benefits for affect thanwalking in urban settings (Berman et al., 2008; Bratman et al., 2015;
Hartig et al., 2003; Janeczko et al., 2020; Koselka et al., 2019). To
illustrate, Bratman et al. (2015a) found that healthy young adults (meanage = 22.9 years) who walked in nature (n = 30) for 60 min reported agreater decrease in negative affect and increase in positive affect frombefore to immediately after the walk compared to those who walked inan urban environment (n = 30) for the same duration. To our knowl­edge, only one prior study has examined whether a walk in nature (vs. awalk in urban settings) can improve the affect (i.e., decrease negative
affect and increase positive affect) of adults diagnosed with depression.
Using a within-subjects randomized crossover design with 19 adults
diagnosed with depression, a study by Berman et al. (2012) found that
positive affect increased to a greater extent after a 50-min nature walkvs. an urban walk alongside a busy public road, whereas negative affectimproved (i.e. decreased) for all participants, regardless of walkcondition.
The present study aims to evaluate the effects of a single 60-min walkin nature (i.e., in a large, biodiverse park) versus urban settings (i.e.,alongside a busy public road) on levels of negative and positive affect inadult psychiatric outpatients with MDD, using a rigorous randomized
controlled protocol. Clarifying whether such findings can be replicatedin a population of psychiatric outpatients with MDD could inform thedevelopment of complementary strategies to alleviate depressive
symptoms. While virtually all prior studies on the effects of one nature
walk (vs. one urban walk) (Berman et al., 2008, 2012; Bratman et al.,2015; Janeczko et al., 2020) only measured affect immediately before
and after the walk, our study will further extend prior knowledge byusing repeated assessments of affect, including measures at mid-point
during the walk; immediately after the walk; and at several points
post-walk (the same day before going to bed; the next morning; and twodays later) to assess short-term effects.

if they had imminent suicidal risk (i.e., desire and intent, as well as thecapacity of carrying out intent within 48 h); a lifetime history of psy­
chotic disorders; or a heart or serious medical condition (e.g., major
surgery) that might impede their ability to walk for an hour. At the timeof the trial, all participants were receiving care from the psychiatrichospital’s medical team, which includes psychiatrists, nurses, psychol­ogists, and social workers.
Of the 47 recruited participants, 10 dropped out prior to completing
their scheduled walk and 37 completed the walk (see Fig. 1). Partici­
pants who completed the walk and were included in the analyses (n =37) were not different from those who dropped out prior to theirscheduled walk (n = 10) in terms of sex (p = .889), age (p = .729), andseverity of depressive symptoms at baseline (p = .856) assessed using the
Hamilton Depression Rating Scale (Hamilton, 1967). Among the 37
participants who completed their walk (including the first three as­
sessments: Pre-Walk, During the Walk, and Immediately Post-Walk), 32
participants completed the assessments at Time 4 (Before Bedtime) and5 (24 Hours Post-Walk) and 29 participants completed the assessments
at all 6 time points (including Time 6, 48 Hours Post-Walk). Of the 37
participants who completed the walk, 20 were randomized to the nature
walk condition and 17 to the urban walk condition.
2.3. Randomization
Participants were randomized to the condition groups (nature walkvs. urban walk) using a computerized randomization procedure (www.
keamk.com) with a 1:1 allocation ratio. This study is a single-blind RCT;
as such, only the participants were blind to the randomization condi­
tions. In the process of obtaining informed consent, participants weretold that the goal of the study was to examine the impact of different
outdoor walk routes on depressive symptoms. The research assistants
conducting the assessments and guiding the walks were not blind toparticipants’ assigned walk condition.
2.4. Walk conditions
Walks took place from May 20th to October 23rd in 2019 and from
June 21st to August 20th in 2021 in the morning, between 8 am and 12
pm (the study was interrupted in 2020 due to the COVID-19 pandemic).
Participants went on one scheduled walk, individually or in groups oftwo, while accompanied by two research assistants (psychology under­
graduate/graduate students). They walked for approximately 60 min ata pace of 3-5 km/h and were instructed to refrain from engaging inconversation to minimize social stimulation and maximize their focus on
the surrounding environment. The settings and duration of the natureand urban walk conditions described below were similar to those used inprior studies (Berman et al., 2008, 2012; Bratman et al., 2015) to in­crease inter-study comparability. In the case of heavy rain, walks were
rescheduled to the participants’ next availability. Information on theweather (sunny / partly sunny, cloudy/partly cloudy) was obtained via
Environment Canada (see Supplemental Table 1). Both the nature andurban walk conditions were similar in terms of weather conditions(recorded from Environment Canada) and perceived levels of physicalexertion, as reported by the BORG CR-10 scales (Borg, 1998) completed
by participants immediately after each walk (participants were asked toanswer the question “How was the walk?” by circling a number on ascale ranging from 0-No exertion at all to 10-Maximal exertion; see Sup­
plemental Table 1). All participants completed their walk in its entirety.
The nature walk took place in a 97-hectare biodiverse urban parknear the psychiatric hospital. The total distance of the nature walk was
4.41 km with a cumulative elevation of 13 m and lasted approximately
60 min. The distance between the psychiatric clinic building entrance tothe park entry was 0.92 km, 0.77 km of which was spent crossing theclinic parking lot. As such, participants walked for about 14 min before
reaching the park entrance. The walk included a stretch of 3.5 km within
the park far from urban sounds (e.g., automobile noise) and sights (e.g.,

2. Method
2.1. Ethics statement
The study was approved by the ethics board of the Douglas Mental
Health University Institute. Participants provided written informed
consent and were compensated up to $75 for their participation. Thisrandomized controlled trial (RCT) using parallel group design is regis­
tered at ClinicalTrials.gov (NCT03996785). Changes made to the study
protocol due to the COVID-19 pandemic are detailed in the supple­
mental material.
2.2. Participants
A total of 47 participants were recruited in 2019 and 2021 from atertiary psychiatric outpatient clinic for adults with refractory major
depressive disorder, most of the time accompanied by suicidal ideation,at the Douglas Mental Health University Institute (DMHUI) in theprovince of Quebec, Canada. Patients were eligible to participate in thisstudy if they were between the ages of 18 to 65 years old; had a primary
diagnosis of MDD (as per their medical chart according to the Structured
Clinical Interview for Axis I DSM-IV, SCID I; First, 1997); were able towalk for 1 h; had the ability to complete online follow-up question­
naires; and were fluent in English or French. Participants were excluded292

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Journal of Affective Disorders 318 (2022) 291–298

Fig. 1. CONSORT diagram of participants’ progress through the study.

buildings and parked automobiles). The park consists of a forest of withover 20,000 trees as well as a pond, and no automobiles are permitted
within the vicinity of the park.
The urban walk took place on the sidewalks of the busiest street near
the psychiatric hospital with 3–4 lanes of automobile traffic. Partici­
pants walked west on this street and completed a short loop at the
midpoint of the walk within the residential streets and then turned backaround, in order to match the distance of the nature walk (see Fig. 2).
The total distance of the urban walk was 4.46 km with a cumulative
elevation of 8 m. Participants walking on this route were exposed to asignificant amount of noise generated by automobiles.

2.5. Assessments
Following randomization, the assessments first took place at thehospital in the hour preceding the scheduled walk (Time 1, “Pre-Walk”);
during the walk at midpoint (Time 2, “During the Walk”); immediately
after the walk at the hospital (Time 3, “Immediately Post-Walk”); later inthe evening at home (Time 4, “Before Bedtime”); the morning after the
walk (Time 5, “24 Hours Post-Walk”); and 48 h after the walk (Time 6,“48 Hours Post-Walk”). Assessments at Times 1, 2, and 3 werecompleted on an iPad carried by the research assistant accompanying
participants on their walk. The iPad was handed to participants at theassigned times with the appropriate questionnaire already displayed on
the screen. Participants immediately returned the iPad to the research
assistant upon completion of the questionnaire and resumed their walk.
293

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Journal of Affective Disorders 318 (2022) 291–298

Fig. 2. GoogleMaps overview of the nature walk condition and the urban walk condition.
Note: The nature condition walk route is highlighted in green. The urban condition walk route is highlighted in red. (For interpretation of the references to colour inthis figure legend, the reader is referred to the web version of this article.)

Assessments at Times 4, 5, and 6 were completed by participants using
their own devices at home. Participants received individual e-mail re­minders with the specific online link for each questionnaire.

terms of baseline sociodemographic and clinical characteristics,
including the severity of depressive symptoms assessed by the HAM-D(Hamilton, 1967). Therefore, none of these variables were included in
the main analyses as covariates. However, differences in negative (butnot positive) affect between conditions were detected at all time points,
including at Time 1 (Pre-Walk; p = .022), with participants assigned to
the nature walk condition showing lower levels of negative affect atbaseline than those assigned to the urban walk (see Table 2). Thus, PreWalk affect (both positive and negative) was controlled for in all sta­tistical models.
We performed two repeated measure mixed model analyses to test
the effects of a single walk in nature vs. urban settings on negative andpositive affect while controlling for baseline affect at Time 1 (Pre-Walk).
For negative affect, results indicated that there was no significant
interaction between Condition and Time on negative affect, F(4,128.729) = 1.223, p = .304, and no main effect of Time, F(4, 128.736) =0.471, p = .757. However, there was a significant main effect of con­dition, F(1, 35.039) = 4.239, p = .047. As illustrated in Table 3 andFig. 3, after adjusting for Pre-Walk (Time 1) levels of negative affect,
participants who walked in nature reported overall lower levels ofnegative affect than those who walked in urban settings. For positive
affect, results indicated no statistically significant Condition x Timeinteraction, F(4, 127.131) = 0.752, p = .559, and no significant main
effect of Condition, F(1, 33.662) = 0.393, p = .535. However, there wasa significant main effect of time on positive affect, F(4, 127.556) =6.059, p < .001 (see Table 3 and Fig. 4) after adjusting for Pre-Walk(Time 1) levels of positive affect, indicating that positive affectdecreased over time – returning to baseline levels – across walk condi­
tions. In sensitivity analyses, we reran mixed models on both negativeand positive affect while removing the Before Bedtime (Time 4) time­
point, as participants went to bed at different times (range: 6:07 pm to
8:40 am; median: 9:11 pm). However, the pattern of results remained
similar (data not shown).

2.5.1. Primary and secondary outcomes
The study’s primary and secondary outcomes were negative andpositive affect, respectively, as measured by the Positive and Negative
Affect Schedule (PANAS; Watson et al., 1988). The PANAS is a widelyused 20-item self-rated questionnaire measuring positive (e.g.,“excited”) and negative (e.g., “upset”) affect (positive affect scale, α:0.88–0.93; negative affect scale, α: 0.89–0.93). Participants indicated towhat extent they feel each affect “right now—that is, at the present
moment” with response choices ranging from 1 (very slightly or not at all)to 5 (extremely). The PANAS was administered via iPad at all 6 time
points of the study: Pre-Walk (Time 1), During the Walk (Time 2),
Immediately Post-Walk (Time 3), Before Bedtime (Time 4), 24 Hours
Post-Walk (Time 5), and 48 Hours Post-Walk (Time 6).
2.6. Statistical analyses
First, we compared participants assigned to the nature vs. urban walkcondition on baseline sociodemographic and clinical characteristics
using 2-tailed t-tests for continuous measures and chi-square tests for
categorical measures. Second, we examined differences in both negativeand positive affect between walk conditions using 2-tailed t-tests. Third,
we evaluated the effects of walk condition on negative and positive
affect using two repeated measure mixed model analyses with Condition(i.e. walk condition; nature vs. urban) as the between-subject factor andTime as the within-subject factor. Mixed models are ideal for analyzing
repeated measures data and can accommodate for missing data via theFull Information Maximum Likelihood (FIML) method while using all
available observed measurements (Detry and Ma, 2016; Enders, 2001).
All analyses were conducted using SPSS, version 28, and the threshold ofsignificance was set at p < .05.

4. Discussion

3. Results

Using a robust RCT design, this study suggests that walking in nature(vs. in urban settings) can lower negative affect in adults with MDD

As shown in Table 1, participants in both conditions were similar in294

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Journal of Affective Disorders 318 (2022) 291–298

recruited from a psychiatric outpatient clinic for refractory depression.
Our results showed that after controlling for baseline differences inaffect, participants who walked in nature experienced less negative
affect overall (but no difference in positive affect) compared to those
who walked in an urban setting.
Overall, our findings indicating lower levels of negative affect inparticipants who walked in nature relative to those who walked along anurban route are in line with results from other experimental studies
conducted with non-depressed populations (Berman et al., 2008; Brat­
man et al., 2015; Janeczko et al., 2020; Koselka et al., 2019). To ourknowledge, the 2012 study by Berman and colleagues is the only otherstudy (using a within-subjects randomized crossover design, in ourcontrast to our parallel group design) that has examined the effect of awalk in nature vs. a walk in urban settings on both negative and positive
affect of young adults diagnosed with MDD (n = 19; 12 females; mean
age = 26 years; Berman et al., 2012). Unlike our findings indicating
lower levels of overall negative affect (with no difference in positive
affect) among participants who walked in nature, Berman and col­leagues’ results showed a greater improvement in positive affect among
participants who walked in nature (vs. in an urban setting), with nocondition difference in terms of negative affect. It is worth noting thatparticipants in Berman and colleagues’ study were primed to ruminate
about a negative autobiographical experience just prior to the walk,which may have interfered with anticipated benefit of nature exposure
on participants’ negative affect. Further, although Berman’s participants
were diagnosed with MDD, they were recruited from the community,
not a psychiatric hospital. It is plausible that our participants, all psy­
chiatric outpatients with a formal diagnosis of MDD, showed changes inTable 1Baseline sociodemographic and clinical characteristics of participants by walkcondition.
Participantcharacteristics
Sex, % (n)MaleFemaleAge in years, M (SD)
Civic status, % (n)In a relationshipSingleLiving situation, %
(n)
Alone
With others
Last education levelobtained, % (n)High school diploma
or less
Higher education(college; university)
Current occupation,% (n)aEmployed/studying
Not employed/
studying
Past psychiatrichospitalizations, %
(n)
Yes
No
Current psychiatric
medications, % (n)YesNo
Depressive symptoms
severity, M (SD)b
Nature relatedness,
M (SD)cWhole
sample (n= 37)Naturewalk (n =
20)

Urban
walk (n =17)32.4 (12)67.6 (25)49.27(10.95)35.0 (7)65.0 (13)48.20(11.21)29.4 (5)70.6 (12)50.53(10.85)35.1 (13)64.9 (24)40.0 (8)60.0 (12)29.4 (5)70.6 (12)27.0 (10)73.0 (27)30.0 (6)70.0 (14)23.5 (4)76.5 (13)37.8 (14)35.0 (7)41.2 (7)62.2 (23)65.0 (13)58.8 (10)P values forurban vs nature
walk condition
.717
.526
.501
.659

.699

.915
27.0 (10)67.6 (25)25.0 (5)65.0 (13)29.4 (5)70.6(12).769

37.8 (14)62.2 (23)40.0 (8)60.0 (12)35.3 (6)64.7 (11)91.9 (34)
8.1 (3)15.43(5.88)
3.82 (.82)

100 (20)–
15.25(5.37)
3.78 (.86)

82.4 (14)17.6 (3)15.65(6.60)
3.87 (.79).050Table 3
Repeated measures mixed model summary table examining the effects ofwalking in the nature condition and urban condition on negative and positive
affect over time, while adjusting for Pre-Walk (Time 1) levels of negative andpositive affect; n = 37.

.844
.741

FactorNote: We conducted an intake interview (conducted in person in 2019 and overthe phone in 2021 due to the ongoing COVID-19 pandemic) to assess socio­
demographic characteristics via a questionnaire and severity of depressive
symptoms in the last week.
a
2 participants answered “I don’t know”.
b
Assessed via the Hamilton Depression Rating Scale (Hamilton, 1967)
administered by a trained research assistant within 30 days prior to the walk.
c
Assessed via the Nature Relatedness Scale-Short Form (NR-6; e.g., “I takenotice of wildlife wherever I am”; (Nisbet and Zelenski, 2013) completed byparticipant at Time 1 or pre-walk.

Negative affectdfTimeCondition
Time ×condition

4,
128.736
1, 35.039
4,
128.729

Positive affect

F

p

df

F

p

.471

.757

4, 127.556

6.059

<.001

4.239
1.223

.047
.304

1, 33.662
4, 127.131

.393
.752

.535
.559

Note.
Covariate: time 1 (pre-walk).
Time: time 2 (during the walk); time 3 (immediately post-walk); time 4 (before
bedtime); time 5 (24 hours post-walk); and time 6 (48 hours post-walk).
Condition: nature walk; urban walk.

Table 2Means and standard deviations for positive and negative affect scores in the nature and urban condition at Pre-Walk (Time 1), During the Walk (Time 2), Immediately
Post-Walk (Time 3), Before Bedtime (Time 4), 24 Hours Post-Walk (Time 5) and, 48 Hours Post-Walk (Time 6).
Negative affectPositive affectTime

Nature condition M (SD)

Urban condition M (SD)P values

Nature condition M (SD)

Urban condition M (SD)P values

Pre-walka
During the walkb
Immediately post-walkc
Before bedtimed
24 hours post-walke
48 hours post-walkf

18.80 (6.80)
13.45 (3.61)
12.00 (2.69)
13.78 (5.22)
15.00 (5.37)
16.28 (6.94)

25.06 (9.07)
17.77 (7.63)
17.11 (6.96)
21.00 (8.65)
23.25 (7.66)
23.33 (9.12)

.022
.031
.005
.005
<.001
.017

22.95 (7.58)
25.80 (8.65)
24.45 (10.24)
21.72 (9.34)
20.44 (9.07)
20.67 (7.82)

23.06 (7.60)
28.59 (6.97)
27.18 (7.28)
22.41 (7.22)
22.06 (9.26)
21.13 (6.88)

.966
.294
.565
.809
.611
.858

Note. Based on maximum n available for each time point.
aNature Condition, n = 20; Urban Condition, n = 17.
bNature Condition, n = 20; Urban Condition, n = 17.
cNature Condition, n = 20; Urban Condition, n = 17.
dNature Condition, n = 18; Urban Condition, n = 17.
eNature Condition, n = 18; Urban Condition, n = 16.
f
Nature Condition, n = 18; Urban Condition, n = 15.
295

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Journal of Affective Disorders 318 (2022) 291–298

24

Adjusted Negative Affect Mean

22
20
18
16
14
12
10
During the Walk

Immediately PostWalk

Before Bedme

24 Hours Post-Walk 48 Hours Post-Walk

Time Points
NatureUrban

Fig. 3. Adjusted mean negative affect levels During the Walk (Time 2), Immediately Post-Walk (Time 3), Before Bedtime (Time 4), 24 Hours Post-Walk (Time 5), and48 Hours Post-Walk (Time 6), while controlling for Pre-Walk (Time 1); n = 37.
Note: Adjusting for negative affect prior to the walk, there was a significant overall main effect of walk condition on negative affect, F(1, 35.039) = 4.239, p = .047;
but no main effect of Time or Time x Condition interaction; see Table 3.

32
30

Adjusted Positive Affect Mean

28
26
24
22
20
18
16
During the Walk

Immediately PostWalk

Before Bedme

24 Hours Post-Walk

48 Hours Post-Walk

Time Points
NatureUrban

Fig. 4. Adjusted mean positive affect levels During the Walk (Time 2), Immediately Post-Walk (Time 3), Before Bedtime (Time 4), 24 Hours Post-Walk (Time 5), and48 Hours Post-Walk (Time 6), while controlling for Pre-Walk (Time 1); n = 37.
Note: Adjusting for positive affect prior to the walk, there was a significant time effect (F(4, 127.556) = 6.059, p < .001); but no significant overall main effect of walkcondition or Time x Condition interaction; see Table 3.

affect that are typical of individuals with more severe depression.
Indeed, prior studies have shown that individuals suffering fromdepression report lower levels of positive emotion compared to nondepressed people during exposure to positive stimuli (Berenbaum andOltmanns, 1992; Bylsma et al., 2008; Horner et al., 2014; Pizzagalli
et al., 2008; Rottenberg, 2005; Rottenberg et al., 2002; Sloan et al.,
1997; Vanderlind and Joormann, 2019) and the presence of greater
depressive symptoms is correlated with higher levels of positive emotion
dampening (i.e., active or passive attempts to downregulate positive

emotion after it has been elicited; Eisner et al., 2009; Feldman et al.,2008; Nelis et al., 2015).
4.1. Strengths and limitations
To the best of our knowledge, our study is the first to examine theeffects of a single walk in nature (vs. urban settings) on the affect of an
adult psychiatric outpatient population with MDD. Other strengths
include its’ single-blind RCT study design; the use of a standardized
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Journal of Affective Disorders 318 (2022) 291–298

measure of positive and negative affect; the prospective data collection
at six points in time; and the use of an urban park (i.e., a large, bio­diverse park found in an urban setting) to assess the impact of nature
exposure while walking, as urban parks are likely to be more accessible
to city residents than countryside settings. We nevertheless acknowl­edge the following limitations. Our preliminary analyses revealed
baseline differences in levels of negative affect between participants inthe nature vs. urban walk conditions (there was no observed baseline
difference in positive affect). In this single-blind RCT, participants wereblind to their assigned walk condition – indeed, while they were told in
the process of obtaining informed consent that the goal of the study was
to examine the impact of different outdoor walk routes on depression,
participants were not made aware of the explicit aim to compare theeffects of walking in nature vs. urban settings. While the research as­sistants administering assessments and guiding the walks were not blind
to participants’ assigned walk condition, the baseline assessment ofaffect was administered via iPad to participants within the first 15 min of
their arrival to the testing session, following very minimal interaction
with the research assistant. It is therefore unlikely that participants’interactions with research assistants who knew of their assigned walkcondition would have impacted observed baseline levels of negative
affect. Moreover, we controlled for these baseline differences in our
subsequent analyses. The presence of more female than male partici­
pants limited our ability to generalize our findings to male participants.
Like other studies examining the impact of walking in nature on affect,
our Pre-Walk (Time 1) measurements were assessed in a laboratory
setting instead of at participants’ homes which may have impacted theaccuracy of baseline measurements in reflecting true, day-to-day base­line affect. Participants in the nature walk condition had to walk througha parking lot and across a busy road for 14 min before reaching thenature setting. However, this may increase the generalizability of find­ings given that most city dwellers must travel by foot or vehicle in orderto reach a natural environment.

Humanities Research Council (SSHRC). Dr. Pennestri (Junior 2) and Dr.
Malboeuf-Hurtubise (Junior 1) hold salary award from the Fonds derecherche du Québec en santé (FRQS). Drs Gouin, Ouellet-Morin, andGeoffroy each hold a Canada Research Chair, Tier 2.

4.2. Clinical implications and conclusion

Acknowledgements

Altogether, our results suggest that walking in nature might be auseful complementary strategy to improve negative affect in the shortterm for individuals diagnosed with MDD. Prior evidence suggests thatwilderness therapy (e.g., Bettmann et al., 2016) and group walks innature can serve as complementary treatment options for adults withdepression (e.g., see Keenan et al., 2021; Sturm et al., 2012). To illus­
trate, a crossover trial with 20 participants having attempted suicide atleast once reported a reduction in depressive symptoms and hopeless­ness after a 9-week hiking intervention vs. a 9-week control phase(Sturm et al., 2012).
The precise mechanisms by which nature exposure might influence
human affect remain unclear, although several candidates – such as
reduced stress and rumination and increased sleep and exercise – havebeen documented (Markevych et al., 2017; Owens and Bunce, 2022).
Further investigation of these potential mediators, as well as the optimal
elements and doses of nature exposure, would enable clinicians to target
key processes and improve the efficacy of nature-based interventions(Owens and Bunce, 2022). A recent systematic review synthesizing theeffects of nature walks for depression and anxiety revealed that themethodological quality of the current body of research is inconsistentand sample sizes are small (Kotera et al., 2021). Thus, there is a need forwell-designed, large-scale studies on the causal relationship between
nature exposure and depressive symptoms and the different ways inwhich to integrate the beneficial effects of nature exposure into existingtreatment plans for adult psychiatric outpatients with major depressive
disorder.

The authors thank Alain Girard, MSc, for his contributions to thestatistical analyses as well as all the participants of the study.

Data availability statement
The data that support the findings of this study are available on
request from the corresponding author. The data are not publicly
available due to privacy or ethical restrictions.
Credit authorship contribution statement
Each author has sufficiently contributed to the manuscript to justify
authorship and responsibility for the content. Kia Watkins-Martin,
Stéphane Richard-Devantoy, Frederick Philippe, Isabelle Ouellet Morinand Marie-Claude Geoffroy conceived and designed the study. Kia
Watkins-Martin, Despina Bolanis, Stéphane Richard-Devantoy, Julie
Guindon, and Marie-Claude Geoffroy collected the data. Kia WatkinsMartin and Marie-Claude Geoffroy analyzed the data and all of the au­thors interpreted the data. Kia Watkins-Martin and Marie-Claude
Geoffroy wrote the manuscript and Despina Bolanis, Stéphane
Richard-Devantoy, Marie-Hélène Pennestri, Catherine MalboeufHurtubise, Frederick Philippe, Julie Guindon, Jean-Philippe Gouin,
and Isabelle Ouellet-Morin revised the paper for important intellectual
content. All of the authors read and gave their final approval of theversion to be published and agreed to be accountable for all aspects of
the work.
Conflict of interest
None.

Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.jad.2022.08.121.
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Funding
This project was financially supported by the Social Sciences and297

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