Full length articleNatural outdoor environments and mental and physical health: Relationships and mechanisms
Introduction
Natural outdoor environments, especially green spaces, have been associated with better objective and subjective physical health including: self-perceived health (Maas et al., 2006, Mitchell and Popham, 2007, De Vries et al., 2013, De Vries et al., 2003, Wheeler et al., 2012, Maas et al., 2009, Mitchell et al., 2011), well-being (White et al., 2013a), longevity (Mitchell et al., 2011, Mitchell and Popham, 2008), cardiovascular diseases (Pereira et al., 2013, Tamosiunas et al., 2014), recovery from illness (Ulrich, 1984), symptoms experienced (De Vries et al., 2003), and birth outcomes (Donovan et al., 2011, Dadvand et al., 2014) among others.
Natural outdoor environments have also been associated with better mental health including: general mental health (De Vries et al., 2013, Strum and Cohen, 2014), psychological well-being (Kaplan, 2001); perceived mental health (De Vries et al., 2003, White et al., 2013a, Sugiyama et al., 2008, Richardson et al., 2013, Alcock et al., 2014), anxiety (Beyer et al., 2014, Chang and Chen, 2005), stress, depression, and/or anxiety symptoms (Beyer et al., 2014, Reklaitiene et al., 2014), anxiety or mood disorder treatment (Nutsford et al., 2013), and stress-related illnesses (Grahn and Stigsdotter, 2003). Most of the available studies on the impact of natural outdoor environments on mental health have focused on only one aspect of mental health (De Vries et al., 2003, De Vries et al., 2013, White et al., 2013a, Strum and Cohen, 2014, Sugiyama et al., 2008, Alcock et al., 2014, Chang and Chen, 2005, Reklaitiene et al., 2014, Nutsford et al., 2013, Grahn and Stigsdotter, 2003, Astell-Burt et al., 2014, Van den Berg et al., 2010, White et al., 2013b). These studies therefore lack the comprehensive view that would be provided by considering a full range of indicators.
There is some evidence suggesting that the associations between natural outdoor environments and health might be stronger for low socioeconomic statuses (SES) (Mitchell and Popham, 2007, De Vries et al., 2003, Mitchell and Popham, 2008, Dadvand et al., 2014), and might vary by gender (Tamosiunas et al., 2014, Reklaitiene et al., 2014, Astell-Burt et al., 2014, Richardson and Mitchell, 2010) and degree of urbanization (Mitchell and Popham, 2007, De Vries et al., 2003). But these differences are still not well-established. Moreover, various mechanisms (increasing physical activity (De Vries et al., 2013, Sugiyama et al., 2008, Richardson et al., 2013), increasing social contacts (De Vries et al., 2013, Maas et al., 2009, Sugiyama et al., 2008), increasing restoration/stress reduction (De Vries et al., 2013, Roe et al., 2013), and decreasing environmental hazard exposure (Dadvand et al., 2012a)) have been suggested to explain the associations between green space and health (De Vries et al., 2013), but there is not a clear understanding of them yet (Nieuwenhuijsen et al., 2014, Hartig et al., 2014). Furthermore, little research has been conducted regarding types or characteristics of green spaces that may improve people's health (De Vries et al., 2013, Nieuwenhuijsen et al., 2014, Adevi and Grahn, 2011). Most of the existing studies have been performed in the northwest of Europe and the US, and the applicability of their conclusions to other parts of the world is uncertain (Nieuwenhuijsen et al., 2014). Finally, most of available evidence on the health effects of natural outdoor environment has focused on green spaces and the available studies on potential health benefits of blue spaces (i.e. sea, lakes, urban water bodies, etc.) are still very scarce (Nieuwenhuijsen et al., 2014).
The overarching aim of this study was to evaluate the association between natural outdoor environments (separately for green and blue spaces) and health (general and mental). We also investigated whether this association was modified by the degree of urbanization, gender or socioeconomic status and mediated by physical activity or social support.
Section snippets
Study population
Our study used data from adults being interviewed at the first five campaigns (2010–2012) of the ESCA (Enquesta de Salut de Catalunya) (n = 8793) (Supplementary materials — page 8). The ESCA is a multistage stratified randomized population-based survey in Catalonia, Spain. Catalonia is located in the north-east of the Iberian Peninsula, with an area of 32,107 km2 and 7,478,968 inhabitants in 2013 (Generalitat de Catalunya, 2014). It has a Mediterranean climate characterized by hot and dry summers,
Study population
Of 18,525 adults who were approached, 9408 (50.79%) completed the survey, from whose 8793 (93.46%) were able to be geocoded. The characteristics of study participants, prevalence of outcomes, and description of indicators of natural outdoor environment are presented in Table 1. There were no notable differences in the characteristics of the sample between observed and imputed values (Supplementary material — Table 1).
Main analysis
The indicators of access to green spaces and of surrounding greenness within
Discussion
This study investigated the association between natural outdoor environments, separately for green and blue spaces, and health, including both general and mental health. We also evaluated the potential for modification of these associations by the degree of urbanization, gender, and SES and mediation of these associations by physical activity and social contacts. We found that higher residential surrounding greenness and living in vicinity of green spaces were associated with better health,
Conclusions
In conclusion, our study provides evidence that green spaces are associated with better self-perceived general and mental health across different degrees of urbanization, socioeconomic statuses, and genders, and that physical activity and social support were unlikely to be mediators as they did not show an association with green space indicators. Our observations for health benefits of blue spaces were not conclusive. Our findings for green spaces, together with evidence of previous studies,
Contributorship
MTM participated in the conception, design and planning of the study, performed literature revision, data analysis, interpretation of the results and manuscript writing. PD contributed in the conception, analysis and writing of the manuscript. MC contributed in the geocoding process, derived measures of natural outdoor environment exposure, degree of urbanization and household socioeconomic status, and contributed to manuscript writing. DM guided statistical analysis and contributed in
Funding
This study has received funding from the European Community's Seventh Framework Programme (FP/2007–2013) under grant agreement no: 282996 (ENV.2011.1.2.3-2). Margarita Triguero-Mas is funded by a pre-doctoral grant from the Catalan Government (AGAUR FI-DGR-2013). None of the funders had involvement in the design, analysis or interpretation of this study.
Competing interests
None.
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