Review

Walking on sunshine: scoping review of the evidence

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for walking and mental health
Paul Kelly,1 Chloë Williamson,1 Ailsa G Niven,1 Ruth Hunter,2 Nanette Mutrie,1
Justin Richards3

►► Additional material is Abstract walking, whilst evident, have been surprisingly

published online only. To view Background/objectives  Walking has well-established little studied’.7 Addressing this gap in knowledge
please visit the journal online
(http://d​ x.​doi.o​ rg/​10.​1136/​ positive relationships with, and effects on, physical is important as walking is an accessible behaviour
bjsports-​2017-​098827). health. In contrast, while poor mental health contributes conducted by all ages and sexes, and as such one
substantially to global health burden, an overview of the with great public health potential.8
1
Physical Activity for Health benefits from walking has not previously been published. Consequently, the aims of this review are to
Research Centre, Institute for i. provide an overview of what has been learnt in
We aimed to scope the literature and present what is
Sport, Physical Education and
Health Sciences, University of known, and highlight what is not known, about walking the intervening 20 years in regard to preventing
Edinburgh, Edinburgh, UK and mental health. mental ill-being, promoting mental well-being
2
Queen’s University Belfast, Methods  Design: Scoping review.  Data sources: and intervention effects;
Belfast, UK Ovid (Medline), ProQuest, Web of Science.  Screening ii. Highlight current evidence gaps and research
3
Charles Perkins Centre &
School of Public Health, and reporting: 13 014 records were identified and priorities.
University of Sydney, Sydney, screened by a team of researchers. Included full texts
New South Wales, Australia were analysed and reported according to mental health Methods
outcome. We adopted the established five-stage scoping
Correspondence to Results  For the 8 mental health outcomes (identified review process proposed by Arksey and O’Malley.9
Dr Paul Kelly, Physical Activity a priori), there were a total of 5 systematic reviews and
for Health Research Centre,
50 individual papers included. Depression had the most
Institute for Sport, Physical Stage 1.1: identify the research question
Education and Health Sciences, evidence and existing systematic reviews were reported.
We formulated the following research question:
University of Edinburgh, Evidence for anxiety, psychological stress, psychological
Edinburgh EH8 9YL, UK; ‘What is known about the associations and effects
well-being, subjective well-being and social isolation
​p.​kelly@​ed.​ac.​uk of walking when considering various specified
and loneliness varied in volume and effectiveness, but
mental health outcomes?’
Received 16 November 2017 no harmful effects were identified. There were no studies
For the purposes of this review, we adopted the
Revised 11 March 2018 for walking and resilience. The setting and context of
following definition of walking which we have used
Accepted 13 March 2018 walking seems to be important variables.
previously: walking was taken to mean all forms
Conclusion  The evidence base that suggests walking
of purposeful or incidental bipedal locomotion
benefits mental health is growing, but remains
within reasonable speed ranges (ie, not running or
fragmented and incomplete for some important
jogging).1
outcomes. Policy and national guidelines should promote
the known mental health benefits of increased walking
and future research should directly address the gaps we Stage 1.2: identify the relevant outcomes
have identified. The review team discussed each mental health
outcome identified in the 2008 Physical Activity
Guidelines Advisory Committee Report for rele-
vance, appropriateness and feasibility for this study.4
Introduction Two authors were chartered psychologists registered
Regular walking is known to confer many physical with the British Psychological Society and provided
health benefits including better physical fitness, expert opinion in this process (NM, AN). Depres-
reduction in disease risk and reduced risk of disease sion (outcome 1 (O1)), anxiety (O2) and self-es-
specific and all-cause mortality.1 2 In addition to teem (O3) were retained. Psychological distress was
physical health, mental health also contributes classified under psychological stress (O4). Well-
substantially to global health burden3 and there is being was split into psychological well-being (PWB)
well-established evidence for the link between phys- (O5) and subjective well-being (SWB) (O6) due to
ical activity and several mental health outcomes.4 established evidence for the differences between
This includes variable levels of evidence for depres- these eudemonic and hedonic constructs.10 11 Resil-
sion, anxiety, psychological distress, well-being, ience (O7) and social isolation and loneliness (08)
cognitive function, dementia, sleep, self-esteem, were added as areas of particular mental health and
chronic fatigue and psychological events.4 public health interest. The outcomes were given
While the link between physical activity and operational definitions as shown in table 1.
mental health is well established,5 6 substantially From the original list, dementia was classified
less is known about the role of walking in this under cognitive dysfunction (including Alzheimer’s
To cite: Kelly P, respect.1 Morris and Hardman identified this and Parkinson’s). These were considered neuro-
Williamson C, Niven AG, gap in their seminal ‘Walking to Health’ paper in logical health rather than mental health3 and were
et al. Br J Sports Med 1997 and stated that ‘The pleasurable and thera- not deemed within the scope of this review. Sleep,
2018;52:800–806. peutic, psychological and social dimensions of chronic fatigue and psychological events were

Kelly P, et al. Br J Sports Med 2018;52:800–806. doi:10.1136/bjsports-2017-098827    1 of 9

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Table 1  Mental health outcomes included in this review

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Outcome Description
Depression Depression is a mood disorder categorised by prolonged periods of low mood, or lack of interest and/or pleasure in normal activities most of
the time. Depression includes dysthymia and major depressive disorder.88
Anxiety Anxiety is characterised by uncomfortable or upsetting thoughts, and is usually accompanied by agitation, feelings of tension and activation of
the autonomic nervous system. It is important to note the distinction between transient anxiety symptoms (state anxiety), persistent symptoms
(trait anxiety) and anxiety disorders: a collection of disabling conditions characterised by excessive, chronic anxiety. Examples of anxiety
disorders are specific phobias, social phobia, generalised anxiety disorder, panic disorder, obsessive-compulsive disorder and post-traumatic
stress disorder.4
Self-esteem Self-esteem is the feelings of value and worth that a person has for oneself. It contributes to overall self-concept as a construct of mental
health.89
Psychological stress Psychological stress or distress can be defined as the unique discomforting, emotional state experienced by an individual in response to a
specific stressor or demand that results in harm, either temporary or permanent, to that person.90
Psychological well-being Psychological well-being links with autonomy, environmental mastery, personal growth, positive relations with others, purpose in life and self-
acceptance. This is often referred to as eudemonic well-being.10
Subjective well-being Subjective well-being is defined as a person’s cognitive and affective evaluations of his or her life. Often referred to as hedonic well-being (and
closely aligned with the construct of happiness).11
Resilience Resilience refers to a steady trajectory of healthy functioning after a highly adverse event or a conscious effort to continue in an insightful and
integrated positive manner as a result of lessons learnt from an adverse experience.91
Social isolation and loneliness Social isolation is described as lack of a social network while loneliness is described as an unfulfilled social need.92

considered important but outside the scope and feasibility of this Search strategy and databases
review. Health-related quality of life (HRQoL) was discussed The strategy was designed to be as comprehensive as possible,
extensively, but ultimately excluded as it contains physical, within the constraints of time and resource.9 We used the
social and mental components. Mood was also not included as outcomes in table 1 to define search terms that were adapted for
it is considered a comparatively transient state that cumulatively each relevant electronic database and combined with common
contributes more broadly to what we have captured in subjective walking terms. Search terms and databases are shown in online
and psychological well-being .12 supplementary table S1. Searches were conducted in October
2017.
Stage 2: identifying relevant studies
Studies were included if they met the following inclusion criteria:
►► research articles in any geographical location or setting
Stage 3: study selection
►► published in English in peer-reviewed academic journals
All identified records were uploaded to the online Covidence
►► specify quantitative effects of walking on the predetermined
software (https://www.​ covidence.​org). Duplicates were auto-
mental health outcomes matically removed. Titles and abstracts were reviewed by two
–– preventive effects (negative outcomes)
researchers (PK, CW) with 20% cross-checked early in the
–– health promotion effects (positive outcomes)
process to assess agreement. Full texts were reviewed inde-
–– intervention effects (all outcomes)
pendently by two researchers (PK, section lead) with conflicts
►► designs including primary research studies (cross-sectional
resolved by a third author.
or longitudinal designs, interventions or natural experiments Scoping reviews are known to be iterative in nature as the
with pre–post measures and a non-walking comparison), researchers become more familiar with the data.9 In this review,
reviews, systematic reviews, scoping reviews and meta-anal- it became apparent that O1: depression had a more mature
yses of suitable primary research studies evidence base, characterised by many studies and a number of
►► include any age groups or sex.
systematic reviews. We therefore changed our methods and
Studies were excluded based on the following exclusion criteria to include only existing reviews for this outcome.
criteria:
►► focus only on clinical groups with a specific physical or Stage 4: charting the data
mental illness or condition that is not the illness or condition For each outcome, key information from the relevant included
being treated with walking, that is, secondary mental health texts was extracted into a standard data form (modified for the
(eg, effects on depression in patients with stroke) depression systematic reviews). Information included author,
►► evidence types including guidelines, unpublished and year, location, design, sample size and characteristics, exposure
ongoing trials, annual reports, dissertations and conference or intervention characteristics, comparator or control character-
proceedings istics, outcome measures and key findings.
►► qualitative and ethnographic designs
►► editorials, opinion pieces, magazine and newspaper articles,
case reports, papers with no primary data. Stage 5: collating, summarising and reporting the results
In studies of participants aged <18 years, pedometers were The analytic framework for collating the data was the eight
not considered measures of walking exposure due to the likely mental health outcomes (see table 1). The aim was to report rele-
large proportion of counts from other common forms of phys- vant information on the volume, nature, distribution and charac-
ical activity (eg, unstructured and structured play, and sporadic teristics of published studies. We used the ‘descriptive-analytical’
movement), but we did retain this as a measurement method method from the narrative tradition, which involves applying
in adults for whom pedometer counts are more likely to reflect a common analytical framework to all the primary research
walking. reports and collecting standard information on each study.9

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Figure 1  Simplified study flow chart (full Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) charts available from
authors on request).

Narrative summaries for each outcome as well as key concepts design was not limited to RCTs. A further recent systematic
and related research gaps were reported. review and meta-analysis looked at the effects of physical activity
on postnatal depression (PND) and weight loss.16 Four of the
Results nine included studies were walking or pram walking (with a
In total, we identified 13 014 records from database searches. fifth including walking) but effects on PND were no better than
For depression we included five systematic reviews, while for comparison groups.
resilience there were no included studies. Across the six other A 2013 systematic review examined modes and settings in
outcomes, there were 50 included papers (see figure 1) though effective physical activity interventions to treat depression,
some studies appeared in more than one outcome. The findings identifying five eligible RCTs.17 The authors concluded that
for each outcome are reported below, with further descriptive indoor or outdoor walking was a beneficial aerobic exercise
information in online supplementary table S2. to treat depression. They recommended at least some supervi-
sion, performed three to four times weekly at a moderate or
Outcome 1: depression self-selected intensity for 30–40 min over a period of at least
Of the outcomes in this review, depression has the most devel- 9 weeks.
oped evidence base. Specifically, we report five systematic
reviews.13–17 There were no reviews of walking and prevention Outcome 2: anxiety
of depression, but a 2013 systematic review of physical activity We identified 14 studies focusing on associations between walking
and the prevention of depression included three prospective and anxiety.22–35 After depression this was the second biggest
studies of walking and all found a protective effect.18–20 Further evidence base. Of five cross-sectional studies, four showed an
studies that distinguish whether there are differential effects for association between walking and lower anxiety scores22–25 while
demographics such as age and gender/sex are needed. one did not.27 Heesch et al. also found dose–response associa-
Considering treatment, Robertson et al concluded from eight tions in prospective models.25
eligible randomised controlled trials (RCTs) that walking was an Four studies investigated the acute effects of walking on
effective intervention for clinical depression with an effect size anxiety and found mixed effects.30–32 35 Five studies compared
of −0.86.14 This can be considered a large effect and is at least walking interventions to a comparison condition over time
comparable to effect sizes found in systematic reviews of exercise (6–12 weeks) and found favourable treatment effects.26 28 29 33 34
interventions for depression.21 This finding strongly supports Overall, walking appears to be beneficial for anxiety. Despite
the use of walking as a treatment for depression, and yet more our attempts to operationalise the meaning of ‘anxiety’ a priori
needs to be known since eight studies in this review remain a this remains a broad construct, which made it difficult to draw
relatively small evidence base when considering representation overall conclusions. Given the magnitude of the global burden of
of all ages, genders and other relevant demographics. anxiety, this may be sufficient rationale for more focused study
A systematic review focused on walking group interventions of walking and anxiety. There is a clear need to develop more
concluded they were effective for reducing depression scores.15 prospective epidemiology that could assess both walking and
However, these findings should be interpreted cautiously as persistent symptoms of anxiety and or clinically defined anxiety
it was not clear if depression was clinically defined and study disorders.

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Outcome 3: self-esteem Outcome 6: subjective well-being

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We identified 11 studies that examined the association between We identified 12 studies focusing on associations between
walking and global self-esteem (GSE).31 36–45 There were two walking and SWB.27 31 35 60–68 There was diversity in how SWB
cross-sectional studies that examined the relationship between was described and measured in the identified papers including
walking and GSE.37 38 Both reported no association. We found life satisfaction, happiness, emotional well-being and affective
no prospective analyses. Two acute studies reported benefit on response. From four cross-sectional studies, three found signif-
GSE following a single bout of walking.31 39 icant associations between higher levels of walking and better
There were seven intervention studies that compared walking SWB.27 60 61 64 Two prospective cohort studies found weak but
condition(s) with another condition over time (8–12 weeks) statistically significant relationships between walking and subse-
with both favourable and null effect findings.36 40–45 Walking quent SWB.63 65
programmes varied in length from 8 weeks to 12 months, and Five studies found positive acute effects for a single bout
in frequency, duration, intensity and progression of dose. Two of walking on indicators of SWB.31 35 66–68 One intervention
studies suggested significant improvement in GSE following compared walking to stretching and toning over 6 months and
walking compared with comparator groups. Three of the studies found equivalent improvements in ‘happiness’ and ‘life satisfac-
suggested significant improvement in GSE following walking, tion’ in both groups.62
but this was no greater than the comparator, and two studies In summary, cross-sectional, prospective cohort and acute
showed no change in GSE. studies indicate an association between walking and SWB. The
Overall, the evidence suggests that walking interventions only long-term intervention study was inconclusive and further
have a positive effect on self-esteem, but observational findings studies are clearly required.
were limited. While not a focus of this review, several of the
included studies also incorporated other measures of self-per- Outcome 7: resilience
ception (eg, physical self-worth) that contemporary theoretical The relationship between physical activity and resilience is
perspectives of ‘self ’ would suggest are more susceptible to emerging,69 with associations shown in undergraduate students69
change following walking than GSE, and particularly in acute and healthy adults.70 However, we identified no published
studies.46 journal articles addressing the association specifically between
walking and resilience.

Outcome 4: psychological stress

Outcome 8: social isolation and loneliness
We identified six studies that examined the relationship between
The topic of ‘social health’ is broad, and for the purposes of
walking and psychological stress.27 32 47–50 One cross-sectional
this scoping review we have restricted the focus to social isola-
study showed a large significant association27 and another
tion and loneliness given their direct impact on mental health.71
showed a small non-significant association.27 Threes studies
We identified five studies.62 72–75 A cross-sectional study found
assessed the acute effects of walking on psychological stress32 49 50
significant positive associations for frequency of contacts with
and findings were contradictory. One 4-week-long intervention
neighbours, neighbours’ social support, neighbourhood involve-
showed promising effects at intervention completion but had no
ment and participation, and walking behaviour.72 However, four
effect at 12-week follow-up.48
intervention studies showed mixed evidence.62 73–75
In summary, there is emerging but limited evidence that
As noted previously,71 76 the social environment is complex and
walking is associated with lower psychological stress in obser-
lacks consensus regarding definitions of core constructs, which
vational studies, and that can be used as a potentially promising
we believe has limited this scoping review. In line with the call to
intervention to decrease psychological stress. It is however clear
action by Hunter et al in this special edition,71 further research
that available evidence is not yet sufficient for firm conclusions.
in this area is required to (1) create a taxonomy providing a
consensus of definitions for core concepts of the social environ-
ment; (2) synthesise this complex evidence base to better guide
Outcome 5: psychological well-being
the development of theory and conceptual models for walking
We identified 11 studies that examined the association between
behaviour and mental health; and (3) develop interventions that
walking and PWB.27 29 51–59 There were three cross-sectional
use walking to promote social interactions to enrich existing
studies that examined the association between walking and
social networks or help create new social networks.
PWB. The findings generally supported a positive association
between PWB and walking.27 55 57 One large-scale longitudinal
study showed positive findings for walking for transport.58 Summary of key findings for mental health outcomes
There were no acute studies. Table 2 summarises the state of the evidence for walking and
Seven RCT studies compared the effects of walking inter- the eight mental health outcomes included in this study. Depres-
ventions on PWB with another condition (typically minimal sion and anxiety are the two outcomes with consistent evidence
intervention) over 10–15 weeks. The findings were mixed with for beneficial effects. Self-esteem, PWB, SWB and psychological
instances of no improvements, no between-group effects and stress have either limited or mixed findings for prevention and
some positive effects for walking.29 51–54 56 59 A targeted review treatment. We found no studies investigating resilience. Social
to understand the differential effects of intervention design and/ isolation and loneliness remains a particularly complex area
or study quality may be required. requiring further conceptual mapping. The volume and distribu-
To conclude, the evidence is limited but promising with tion of study type suggests that there is a particular evidence gap
cross-sectional studies and the one longitudinal study identifying for prospective designs (see figure 2).
positive relationships between walking and PWB. The findings
from the intervention studies are more mixed with only two of Discussion
seven studies demonstrating positive effects on PWB compared We aimed to scope and understand what is known about the
with control groups. associations and effects of walking when considering various

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Context of walking
Table 2  Summary of key findings for mental health outcomes

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A considerable proportion of studies compared the effect of
Outcome Key findings setting or type of walking. Additional papers that did not meet
Depression Systematic review-level evidence for prevention and the inclusion criteria included studies on types of outdoor envi-
treatment ronment,77 green environments compared with urban,78–80
Anxiety Multiple studies showing preventive and treatment forest settings,81 parks compared with woodlands82 and green
effects exercise that included walking.83 They suggested a multitude of
Self-esteem No evidence for preventive effects; mixed evidence for positive effects on a range of mental health outcomes for green,
treatment effects outdoor and natural environments, with variations by types of
Psychological stress Limited but emerging evidence for preventive and green settings.
treatment effects
A 2011 systematic review of indoor versus outdoor exer-
Psychological well-being Limited but emerging evidence for preventive effects;
cise identified 11 studies, 7 of which were walking.84 Outdoor
mixed evidence for treatment effects
walking showed positive effects across a range of mental health
Subjective well-being Emerging evidence for preventive effects and emerging
outcomes compared with indoor walking, as well as increased
but limited evidence for treatment effects
intention for future walking. However, the authors concluded
Resilience No evidence found
that there was still a paucity of high-quality evidence. A 2010
Social isolation and Minimal evidence found, but some promising findings;
loneliness area needs mapping conceptually
systematic review of mental health effects of walking in natural
versus synthetic environments had similar findings.85 Conversely,
the social context, whether walking alone, with friends, partners
or in a group, has not been extensively studied.
specified mental health outcomes. To our knowledge, this is the There was insufficient evidence to draw conclusions on
first review of the evidence of multiple mental health outcomes purpose of walking. This issue may be more critical than physi-
and walking. We have shown areas where the evidence base is ological dose for both effect and public health messaging. Very
well developed, and also areas where it is limited and findings few studies we identified compared, for example, commuter
are mixed. walking to leisure walking or dog walking. Furthermore, the
difference between walking by choice, or necessity, is not well
understood. More needs to be known about the role of context
Key concepts and research gaps in the walking and mental of walking, and this is a clear research priority.
health literature
Having addressed the nature and sources of evidence for
walking and mental health, we then mapped the key concepts Dose of walking
in the included studies and highlighted research gaps and Differential ‘dose–response’ effects by frequency, duration,
priorities.9 These are displayed in figure 3, organised in five intensity and length of intervention or exposure time are not
overall themes: (1) context of walking, (2) dose of walking, yet well understood. More needs to be known about the optimal
(3) study design, (4) demographic effects and (5) conceptual dose of walking to benefit different mental health outcomes and
framework. the relative importance of this factor. Intensity of walking is a

Figure 2  Distribution of studies by outcome.

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Figure 3  Key concepts and research gaps in the walking and mental health literature.

particular area of interest. The differences between a brisk walk, appropriate conceptual framework. The different outcomes, the
a slow shuffle and the differential effects as fitness declines with complexity of the outcomes, the development of ecologically
age and relative intensity of walking increases need to be better valid interventions and understanding the mechanisms could
understood for effective public health messaging and interven- benefit from an agreed framework.
tion. Increasing evidence suggests physiological health effects for There is comparatively less research on mental well-being (eg,
walking differ by intensity;86 it is important to understand if the SWB, self-esteem) as opposed to mental ill-being (eg, depres-
same is true for mental health. sion, anxiety) particularly for interventions. It is important to
Understanding these dose-related factors will be intrinsically note that these are independent mental health constructs rather
linked to how walking is measured. When considering intensity, than descriptors that sit at opposite ends of the same spectrum.
self-report measures can explore perceived intensity, within the While the absence of depression or anxiety is clearly desirable, it
limitations of recall bias, while objective measures like pedom- does not necessarily equate to high levels of SWB or self-esteem.
eters may be able to assess cadence. Measures of pace/speed This mirrors the overall definition of health—not merely the
and associated measurement of aerobic fitness or response may absence of disease, but the presence of well-being—and serves
be required. Our scoping review found that measurement of as a reminder of the holistic nature of public health in practice.
walking varies considerably, and much learning is required in It may also be an important factor to consider when developing
this area. public health messaging that is targeted at behaviour change.
Specifically, positive messages about improving well-being
Study design through walking may resonate more with segments of the popu-
In terms of study design, there are evidence gaps around the lation than the disease-aversion messages that have historically
nature and content of comparison conditions, sample sizes with pervaded the health promotion sector. Further investigation of
many small studies and insufficiently powered analyses of mental the relative contribution of walking to well-being and ill-being
health outcomes as secondary or tertiary outcomes. Selection outcomes is indicated and should also take into the account the
and application of appropriate mental health measures is also a most effective methods to influence physical activity behaviour.
key concept in the literature. The complexity of the mental health domain was a key theme.
To quote one of the included studies, ‘Mental health is a vast and
Demographic effects complex domain, which reaches far beyond symptoms, disorders
The effects of walking by sex, age, socioeconomic status and and diagnoses.’27 Whether studies looking at single outcomes
other important demographics remain a research priority. We could address this domain adequately is for discussion. The
are not able to say if existing evidence is generalisable across reductionist nature of examining these outcomes in isolation
demographics. The potential interaction of demographics with may not be appropriate when considering the interwoven nature
dose and context of walking is another important research gap. of psychological constructs and the high prevalence of comorbid
mental illnesses, while studies with multiple outcomes may be
Conceptual framework for walking and mental health accused of cherry-picking favourable findings. Furthermore,
This review highlights areas where the theory of walking and despite efforts to define different mental health outcomes in the
mental health could be expanded through development of an literature, there appears to be ongoing confusion and conjecture

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in the language to describe these constructs. This was particu- possible we missed some important literature and a broader

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larly challenging when attempting to categorise studies that used search strategy would have identified additional relevant studies.
varying outcome definitions.
To have population-level effects, there is a need to transfer Conclusions
promising laboratory and treadmill findings to ecologically Walking is known to benefit physical health. We have shown
valid, free-living settings. This will require the development of how the evidence base for specific mental health outcomes and
robust programme theory to understand and evaluate delivery benefits has grown since Morris and Hardman’s ‘Walking to
and impact. Similarly, the need to establish and understand Health’ review in 1997.7 In 1997, they stated that ‘the pleasur-
mechanisms of effect is an important priority for future research. able and therapeutic, psychological and social dimensions of
For example, is it the physiological dose of walking that provides walking, whilst evident, have been surprisingly little studied’.
the effect or is walking a vector for increased social contact and Despite the growth in the evidence base, given the importance
support? Or is it a combination of pathways?87 Furthermore, the of mental health, and the evidence gaps identified, we think this
interaction and relative importance of the contextual setting (eg, statement still holds true. We anticipate that this scoping review
forest trail vs urban street) of walking and its underlying purpose will stimulate more research in this area. 
(eg, leisure vs commute) remains unclear.
What are the new findings?
Implications and future research
Our findings suggest that while the gap identified by Morris and ►► Over the last 20 years the evidence base for the beneficial
Hardman has seen a growth in research and evidence, it is not effects of walking for mental health has grown, but remains
as developed as other areas (eg, physiological responses, cardio- fragmented and incomplete for some important outcomes.
vascular disease or all cause-mortality). Nor is it as developed ►► For depression and anxiety, there may be sufficient evidence
as we expected when we began this review. Specifically, once to promote walking to prevent and treat these conditions.
mental health was categorised into individual outcomes, in many ►► There has been more research on the negative disease-based
cases the number of studies found was not high. There remains outcomes (such as depression and anxiety) than for the
a vast number of questions and evidence gaps as summarised in positive well-being outcomes (such as happiness or subjective
figure 3. well-being).
The implications for future research clearly include addressing ►► The evidence base seems to indicate that across the mental
the limited volume and quality of prospective and intervention health outcomes there are additional benefits from walking
studies for each mental health outcome. In terms of policy and outdoors in natural environments compared with indoor,
practice, discussion and expert consensus is required on whether treadmill-based walking.
the current evidence base is sufficient to make recommendations
for walking and mental health. For example, to what extent Acknowledgements  The authors thank Marshall Dozier, Evy Horton and Olivia
could the mental health benefits of walking be included in the Alliott for their help and support.
upcoming update of physical activity guidelines by the UK Chief Contributors  PK conceived the study. PK, NM, AGN, JR and CW designed the
Medical Officers? search strategy. CW conducted searching of databases. PK and CW screened records.
All authors contributed to screening full texts. All authors led analysis and writing for
at least one mental health outcome. PK and CW drafted the full manuscript, and all
Strengths and limitations authors reviewed and approved final submission.
The present study has a number of strengths. It is the first review Funding  This research received no specific grant from any funding agency in the
of such a broad range of mental health outcomes specific to public, commercial or not-for-profit sectors.
walking. It considers both prevention and intervention effects, Competing interests  None declared.
and it identifies the volume and distribution of the evidence Patient consent  Not required.
base. This has shown where we have good evidence for walking,
Provenance and peer review  Commissioned; externally peer reviewed.
and where more research is warranted. We have also mapped the
key concepts and research priorities within the literature. © Article author(s) (or their employer(s) unless otherwise stated in the text of the
article) 2018. All rights reserved. No commercial use is permitted unless otherwise
There are a number of limitations to consider. We only expressly granted.
included quantitative studies. This decision was made as qual-
itative designs address different questions outwith our research
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