Examining the Benefits of Greenness on Reducing Suicide Mortality Rate: A Global Ecological Study

Abstract

Objective: This study applied an ecological-based analysis aimed to evaluate on a global scale the association between greenness exposure and suicide mortality.

Methods: Suicide mortality data provided by the Institute for Health Metrics and Evaluation and the Normalized Difference Vegetation Index (NDVI) were employed. The generalized additive mixed model was applied to evaluate with an adjustment of covariates the association between greenness and suicide mortality. Sensitivity tests and positive-negative controls also were used to examine less overt insights. Subgroup analyses were then conducted to investigate the effects of greenness on suicide mortality among various conditions.

Results: The main finding of this study indicates a negative association between greenness exposure and suicide mortality, as greenness significantly decreases the risk of suicide mortality per interquartile unit increment of NDVI (relative risk = 0.69, 95%CI: 0.59-0.81). Further, sensitivity analyses confirmed the robustness of the findings. Subgroup analyses also showed a significant negative association between greenness and suicide mortality for various stratified factors, such as sex, various income levels, urbanization levels, etc.

Conclusions: Greenness exposure may contribute to a reduction in suicide mortality. It is recommended that policymakers and communities increase environmental greenness in order to mitigate the global health burden of suicide.

Keywords: Normalized Difference Vegetation Index; ecological study; global analysis; greenness exposure; suicide mortality.

Figure 1

Spatial distribution of suicide rate mortality from 2000 to 2016.

Figure 2

Spatial distribution of greenness measurements (NDVI).

Figure 3

Subgroup analysis among different levels of (A) greenness, (B) sex, (C) burden of depressive disorders, (D) economic status, (E) urbanization level, (F) unemployment rate and divorce rate, (G) smoking rate and alcohol consumption in suicide changes per one interquartile unit increment of greenness (NDVI = 0.311). Adjusted variables, including population density, age, sex, burden of depressive disorders, healthcare expenditure rate, unemployment rate (U), divorce rate (D), economic status, educational rate, urbanization rate, smoking rate (S), alcohol consumption (A), population without religion, temperature, PM_2.5, and spatial-temporal autocorrelation. *p < 0.05, **p < 0.01, ***p < 0.001.