Role of physical activity in the relationship between urban green space and health.

OBJECTIVES Local availability of green space has been associated with a wide range of health benefits. Possible causative mechanisms underpinning the green space and health relationship include the provision of physical activity opportunities, the stress-relieving effects of nature and the facilitation of social contacts. This study sought to investigate whether urban green space was related to individual-level health outcomes, and whether levels of physical activity were likely to be a mediating factor in any relationships found. STUDY DESIGN Cross-sectional analysis of anonymized individual health survey responses. METHODS Neighbourhood-level green space availability was linked to 8157 respondents to the New Zealand Health Survey 2006/07 on the basis of their place of residence. Adjusted multilevel models were constructed for four health outcomes which are plausibly related to green space via physical activity: cardiovascular disease; overweight; poor general health; and poor mental health (Short Form 36). RESULTS The greenest neighbourhoods had the lowest risks of poor mental health [odds ratio (OR) 0.81, 95% confidence interval (CI) 0.66-1.00]. Cardiovascular disease risk was reduced in all neighbourhoods with >15% green space availability (e.g. OR 0.80, 95% CI 0.64-0.99 for those with 33-70% green space), However, a dose-response relationship was not found. Green space availability was not related to overweight or poor general health. Overall, levels of physical activity were higher in greener neighbourhoods, but adjustment for this only slightly attenuated the green space and health relationships. CONCLUSIONS Neighbourhood green space was related to better cardiovascular and mental health in a New Zealand Health Survey, independent of individual risk factors. Although physical activity was higher in greener neighbourhoods, it did not fully explain the green space and health relationship.