Associations of neighbourhood greenness with physical and mental health: do walking, social coherence and local social interaction explain the relationships?

Background: Studies have shown associations between health indices and access to "green'' environments but the underlying mechanisms of this association are not clear. Objectives: To examine associations of perceived neighbourhood "greenness'' with perceived physical and mental health and to investigate whether walking and social factors account for the relationships. Methods: A mailed survey collected the following data from adults ( n = 1895) in Adelaide, Australia: physical and mental health scores ( 12- item short-form health survey); perceived neighbourhood greenness; walking for recreation and for transport; social coherence; local social interaction and sociodemographic variables. Results: After adjusting for sociodemographic variables, those who perceived their neighbourhood as highly green had 1.37 and 1.60 times higher odds of better physical and mental health, respectively, compared with those who perceived the lowest greenness. Perceived greenness was also correlated with recreational walking and social factors. When walking for recreation and social factors were added to the regression models, recreational walking was a significant predictor of physical health; however, the association between greenness and physical health became non-significant. Recreational walking and social coherence were associated with mental health and the relationship between greenness and mental health remained significant. Conclusions: Perceived neighbourhood greenness was more strongly associated with mental health than it was with physical health. Recreational walking seemed to explain the link between greenness and physical health, whereas the relationship between greenness and mental health was only partly accounted for by recreational walking and social coherence. The restorative effects of natural environments may be involved in the residual association of this latter relationship.