Linkage between green space structures and mental disorder in Taiwan

A blooming body of researches indicate the green space confers numerous health benefits including alleviation of mental distress. Several recent reviews have summarized and evaluated the growing evidence base. However, most of the previous studies used the vegetation index, and tree cover density as the overall green space exposure indices. In fact, there are still more green space factors affecting human health, including the area, edge, distribution, shape, and proximity; however, very few studies had investigated it; especially, the incidence of the mental disorder. The study aims to investigate the relationship between green space structures and mental disorder in Taiwan. There were two green space indexes were used to be the greenness exposure including quantification green space structures and overall greenness index. First of all, the database of Land Use Investigation of Taiwan was used to select the green space like recreational, forest, and overall green space. After preparation, green space structures indices were calculated accordingly, including Patch Area, Shape Index, Fractal Dimension Index, and Proximity Index by using FRAGSRATS 4 (Computer Softeare Program, University of Massachusetts, Amherst, MA, USA). The overall greenness index including Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) were obtained from the global MODIS NDVI database. In addition, the National Health Insurance Research Database was used to define the study population who were first diagnosed the mental disorders according to ICD-9 codes from 290 to 319. Furthermore, the covariates databases were collected in this study, like air pollution, metrological, socioeconomic status databases. The spearman correlation analysis was used to select the variables through considering the collinearity. Cox proportional hazards models were applied to assess the relationship between green space exposure and mental diseases incidence after adjustments were made for the potential confounders. A negative association was found from most of the green space structures indices in whole Taiwan island. Our findings suggest more surrounding greenness, larger green space, more fragmentation, and more proximity may reduce the risk of mental disorder.