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1. Introduction
Concerns about mental health have been growing worldwide and mental health conditions are reported to depend on many factors, including not only demographic factors [1,2,3] such as socio-economic factors [4,5] and health behaviors, but also ecological environmental factors [6,7,8,9]. However, previous studies on the relationships between mental health and associated factors have usually focused on either objective demographic factors including socio-economic conditions, environmental factors, subgroup populations among inpatients, or on specific age groups such as younger generations [8] or the elderly [2,6,10].
Already, some studies have reported that perceptions of low social status in adults may be involved in the pathogenesis of depression [4] and an index of socio-economic status seems to predict depression symptomatology across European countries [5]. However, most studies related to mental health have focused on depression, and there are few studies related to stress or subjective mental health outcomes. In addition, the health behavior factors may be associated with mental health outcomes in both directions; for instance, physical activity or sufficient sleep may be beneficial while smoking or drinking is harmful.
Evidence for the relationship between availability or quality of green areas in neighborhood environments and mental health has been established through various studies. In several studies, living conditions with surrounding greenery were suggested to have benefits for improving mental health [9,11,12,13]. In addition, community based research on mental health has reported adverse health effects of increased levels of air pollution [8].
Seoul is a megacity in the Republic of Korea composed of 25 districts, with one-fifth of the total national population living there. Although the general health status of Seoul citizens may greatly depend on demographic factors, regional characteristics cannot be ignored. Regarding regional characteristics, environmental conditions such as levels of air pollution or greenness have been regulated by environmental policy. For instance, the Seoul government has promoted policies for decades to increase the number and quality of green spaces and to improve air quality. Although the Seoul government has been attempting to improve the environmental quality in Seoul, improvements in citizen’s living conditions in terms of common mental health outcomes may not be measurable as many studies focusing on mental health outcomes have relied on medical service utilization with doctors’ clinical diagnoses. In addition, accessibility and level...