Original ResearchAn ecological study investigating the association between access to urban green space and mental health
Introduction
As many cities experience poor air quality, water pollution, heat island effects and crowding,1 it is un-surprising that the physical and increasingly, the mental health of urban residents has become of major focus in recent decades. One area of investigation is the relationship between access to urban green space and both physical and mental health benefits.2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 An ‘integrated area comprising natural, semi natural, or artificial green land’,13,p174 urban green space provides an aesthetic place for social and recreational opportunities, which encourages physical activity, enhances social ties and promotes mental and physical recuperation.13, 15
The majority of green space studies evaluate its influence on physical health or general health as the health outcome. Many include a mental health component, but present conflicting findings.5, 8, 12, 16 Importantly, studies in New Zealand found no association between green space and a number of health outcomes, including physical health and cause-specific mortality.8, 12 This suggests that green space and any associations with health outcomes may vary between environments and social contexts,8 for example the role of green space is likely to be more influential within urban environments in contrast to rural areas. Green space research concluded that New Zealand's relative prevalence of natural, green environments and a culture of ‘outdoor holidaying’ in comparison to other regions may reduce the ability to detect associations with health outcomes.8 However, this claim has not been evaluated in relation to mental health. A review of health associations with urban green space concluded that many claims are supported by weak evidence and studies were limited by poor design and failure to exclude confounding factors and bias.1
Much less established is the investigation of the effects of access to and visualization of green space on mental health. General consensus in existing literature finds green space to be negatively associated with poor mental health,5, 11 however it is met with some contention and the causal pathways remain relatively unexplored.1, 2 Mental health is important as it is often a precursor for other chronic conditions and physical health outcomes.17 In New Zealand, approximately 20% of the population suffered from a mental disorder in a 12-month period,18 while anxiety and mood disorders affect 5.7% of Auckland's population.17 Given the contribution of mental illness to the disease burden in New Zealand, it is important to evaluate potentially amenable aspects of neighbourhood environments which might reduce this burden. Three primary theoretical pathways have been identified through which green space may influence mental health.13, 15 First, recreational physical activity, common in green space, promotes positive moods and reduces stress levels.19 Second, both planned and coincidental social interaction often take place in public green spaces and have been shown to improve mental well-being.13 Third, green spaces are seen as places for relaxation and recuperation from stressful activities, which influences stress hormone levels.11
Due to the difficulty in obtaining population-level mental health data, most studies rely on self-reported mental health scoring,20, 21, 22, 23 which often under-estimates mental illness.24 Although some studies have reported no direct relationship between green space and mental health outcomes,2 others have found that active participation in green space,19 the proportion of5, 10, 19, 20 and distance to green space,14 and perceived greenness21 were significantly, positively associated with mental health indicators. For example, a Danish study found that individuals living more than 1 km from green space were 1.42 times more likely to experience stress than individuals living <300 m from green space.14 In addition, some studies have evaluated the green space qualities such as size, naturalness, and popularity which may have mental health benefits,22, 25, 26 yet there are no conclusive findings.
Given this background, the authors aimed to understand the relationship between anxiety/mood disorder treatment and access to green space in an urban setting in New Zealand. To our knowledge, this is the first study to evaluate this relationship in New Zealand. Using a data compiled by Richardson et al. (2010), the authors classified green space as either total or useable, to untangle the potential role of active involvement vs observation of green space. The study did not rely on self-reported mental health data, an improvement over many studies in this field. Instead, data from a linked database of all national administrative databases was used.
Section snippets
Data and methodology
Geographical Information System (GIS) techniques were used to investigate the spatial relationships between green space access and mental health treatment at the meshblock (MB) level, New Zealand's finest aggregation unit. The authors included 3149 of 3247 MBs in Auckland City (excluded Islands). Auckland City was chosen for a number of reasons. Firstly, it is the largest and fastest growing city within New Zealand. Secondly, meshblock are typically homogenous in size (on average 0.04 km2),
Results
The average proportion of green space within buffers of PWCs was 16% for 3 km buffers and 13% for 300 m. Just over 40% of the MBs had <5% of green space within 300 m of the PWC while 20% had less than 1%. Useable green space features made up 12% and 15% of the buffers respectively. The average distance from PWCs was 210 m to useable green space and 198 m to total green space. Table 1 summarizes descriptive statistics by quartiles for each green space access measurement. Although considerable
Discussion
It is hypothesized that green space has positive effects on mental health both through active participation and as a salutogenic environment. This study attempted to quantify these two causal pathways by identifying green spaces as useable or non-useable and total. The study found that better access to green space was associated with a decrease in anxiety/mood disorder treatment counts. Specifically, higher proportions of surrounding green space in the broader neighbourhood and decreased
Acknowledgements
The authors thank the Ministry for the Environment, Land Information New Zealand and the Department of Conservation for access to their land use datasets. Anxiety/mood disorder counts were provided courtesy of the Ministry of Health.
Ethical approval
Not required.
Funding
This research was carried out as part of the GeoHealth Laboratory work programme at the University of Canterbury, funded by the New Zealand Ministry of Health.
Competing interests
None declared.
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