BACKGROUND

There is growing research and policy interest in the potential for using the natural environment to enhance human health and well-being. This resource may be underused as a health promotion tool to address the increasing burden of common health problems such as increased chronic diseases and mental health concerns. Outdoor environmental enhancement and conservation activities (EECA) (for instance unpaid litter picking, tree planting or path maintenance) offer opportunities for physical activity alongside greater connectedness with local environments, enhanced social connections within communities and improved self-esteem through activities that improve the locality which may, in turn, further improve well-being.

OBJECTIVES

To assess the health and well-being impacts on adults following participation in environmental enhancement and conservation activities.

SEARCH METHODS

We contacted or searched the websites of more than 250 EECA organisations to identify grey literature. Resource limitations meant the majority of the websites were from UK, USA, Canada and Australia. We searched the following databases (initially in October 2012, updated October 2014, except CAB Direct, OpenGrey, SPORTDiscus, and TRIP Database), using a search strategy developed with our project advisory groups (predominantly leaders of EECA-type activities and methodological experts): ASSIA; BIOSIS; British Education Index; British Nursing Index; CAB Abstracts; Campbell Collaboration; Cochrane Public Health Specialized Register; DOPHER; EMBASE; ERIC; Global Health; GreenFILE; HMIC; MEDLINE-in-Process; MEDLINE; OpenGrey; PsychINFO; Social Policy and Practice; SPORTDiscus; TRoPHI; Social Services Abstracts; Sociological Abstracts; The Cochrane Library; TRIP database; and Web of Science. Citation and related article chasing was used. Searches were limited to studies in English published after 1990.

SELECTION CRITERIA

Two review authors independently screened studies. Included studies examined the impact of EECA on adult health and well-being. Eligible interventions needed to include each of the following: intended to improve the outdoor natural or built environment at either a local or wider level; took place in urban or rural locations in any country; involved active participation; and were NOT experienced through paid employment.We included quantitative and qualitative research. Includable quantitative study designs were: randomised controlled trials (RCTs), cluster RCTs, quasi-RCTs, cluster quasi-RCTs, controlled before-and-after studies, interrupted-time-series, cohort studies (prospective or retrospective), case-control studies and uncontrolled before-and-after studies (uBA). We included qualitative research if it used recognised qualitative methods of data collection and analysis.

DATA COLLECTION AND ANALYSIS

One reviewer extracted data, and another reviewer checked the data. Two review authors independently appraised study quality using the Effective Public Health Practice Project tool (for quantitative studies) or Wallace criteria (for qualitative studies). Heterogeneity of outcome measures and poor reporting of intervention specifics prevented meta-analysis so we synthesised the results narratively. We synthesised qualitative research findings using thematic analysis.

MAIN RESULTS

Database searches identified 21,420 records, with 21,304 excluded at title/abstract. Grey literature searches identified 211 records. We screened 327 full-text articles from which we included 21 studies (reported in 28 publications): two case-studies (which were not included in the synthesis due to inadequate robustness), one case-control, one retrospective cohort, five uBA, three mixed-method (uBA, qualitative), and nine qualitative studies. The 19 studies included in the synthesis detailed the impacts to a total of 3,603 participants: 647 from quantitative intervention studies and 2630 from a retrospective cohort study; and 326 from qualitative studies (one not reporting sample size).Included studies shared the key elements of EECA defined above, but the range of activities varied considerably. Quantitative evaluation methods were heterogeneous. The designs or reporting of quantitative studies, or both, were rated as 'weak' quality with high risk of bias due to one or more of the following: inadequate study design, intervention detail, participant selection, outcome reporting and blinding.Participants' characteristics were poorly reported; eight studies did not report gender or age and none reported socio-economic status. Three quantitative studies reported that participants were referred through health or social services, or due to mental ill health (five quantitative studies), however participants' engagement routes were often not clear.Whilst the majority of quantitative studies (n = 8) reported no effect on one or more outcomes, positive effects were reported in six quantitative studies relating to short-term physiological, mental/emotional health, and quality-of-life outcomes. Negative effects were reported in two quantitative studies; one study reported higher levels of anxiety amongst participants, another reported increased mental health stress.The design or reporting, or both, of the qualitative studies was rated as good in three studies or poor in nine; mainly due to missing detail about participants, methods and interventions. Included qualitative evidence provided rich data about the experience of participation. Thematic analysis identified eight themes supported by at least one good quality study, regarding participants' positive experiences and related to personal/social identity, physical activity, developing knowledge, spirituality, benefits of place, personal achievement, psychological benefits and social contact. There was one report of negative experiences.

AUTHORS' CONCLUSIONS: There is little quantitative evidence of positive or negative health and well-being benefits from participating in EECA. However, the qualitative research showed high levels of perceived benefit among participants. Quantitative evidence resulted from study designs with high risk of bias, qualitative evidence lacked reporting detail. The majority of included studies were programme evaluations, conducted internally or funded by the provider.The conceptual framework illustrates the range of interlinked mechanisms through which people believe they potentially achieve health and well-being benefits, such as opportunities for social contact. It also considers potential moderators and mediators of effect.One main finding of the review is the inherent difficulty associated with generating robust evidence of effectiveness for complex interventions. We developed the conceptual framework to illustrate how people believed they benefited. Investigating such mechanisms in a subsequent theory-led review might be one way of examining evidence of effect for these activities.The conceptual framework needs further refinement through linked reviews and more reliable evidence. Future research should use more robust study designs and report key intervention and participant detail.