Association between greenness exposure and depression rate among Bangkok residents: An ecological longitudinal study

This ecological study aimed to examine the relationship between greenness exposure and depression among Bangkok residents, using the district as a unit of analysis. This study utilized data on depression (ICD-10 F32, F33), environmental parameters, and demographic and health infrastructure variables in 50 districts in Bangkok recorded from 2018 to 2020. The Excellence Center for Depressive Disorder provided information on the number of new depression cases, including only those who had registered permanent residence in Bangkok. Greenness was measured using the normalized difference vegetation index (NDVI), which was extracted from a Terra-MODIS sensor. Then, the association between greenness exposure and depression was evaluated using descriptive statistics, bivariate analysis, and generalized additive mixed models with adjustment for covariates. From 2018 to 2020, a mean of 4.57 ± 6.45 cases was recorded per 100,000 population annually, and the mean NDVI was 0.33 ± 0.09. Adjusted for all covariates, as well as considering the smooth terms basis, an increase in one unit of NDVI value would contribute to depression rate reduction by up to 77.7 % (risk ratio = 0.223, 95 % CI = 0.200 – 0.248). PM_2.5 exhibited an insignificant positive association with depression incidence rate. Additionally, temperature and humidity were associated with depression rate in the final model (p < 0.05). Living in greener areas would contribute to a lower depression incidence rate in Bangkok. However, the study is subject to limitations, including the impact of the COVID-19 pandemic, which may have influenced both depression rates and access to green spaces during the study period. Policies that can increase environmental greenness should be promoted to enhance social interactions and physical activities.