Long-term exposure to air pollution and the risk of suicide death: A population-based cohort study.

Suicide is a major public health problem. Previous studies have reported a significant association between acute exposure to air pollution and suicide; little attention has been paid to the long-term effects of air pollution on risk of suicide. We investigated whether long-term exposure to particulate matter of ≤10μm in diameter (PM), nitrogen dioxide (NO), and sulfur dioxide (SO) would be associated with a greater risk of death by suicide. The study sample comprised 265,749 adults enrolled in the National Health Insurance Service-National Sample Cohort (2002-2013) in South Korea. Suicide death was defined as per ICD-10 code. Data on air pollution exposure used nationwide monitoring data, and individual exposure levels were assigned using geographic information systems. Air pollution exposure was categorized as the interquartile range (IQR) and quartiles. Hazards ratios (HRs) were calculated for the occurrence of suicide death after adjusting for potential covariates. During the study period, 564 (0.2%) subjects died from suicide. Increases in IQR pollutants (7.5μg/m for PM, 11.8ppb for NO, and 0.8ppb for SO) significantly increased HR for suicide death [PM: HR=3.09 (95% CI: 2.63-3.63); NO: HR=1.33 (95% CI: 1.09-1.64); and SO: HR=1.15 (95% CI: 1.07-1.24)]. Compared with the lowest level of air pollutants (Quartile 1), the risk of suicide significantly increased in the highest quartile level (Quartile 4) for PM (HR=4.03; 95% CI: 2.97-5.47) and SO (HR=1.65; 95% CI: 1.29-2.11) and in the third quartile for NO (HR=1.52; 95% CI: 1.17-1.96). HRs for subjects with a physical or mental disorder were higher than that those for subjects without the disorder. Subjects living in metropolitan areas were more vulnerable to long-term PM exposure than those living in non-metropolitan areas. Long-term exposure to air pollution was associated with a significantly increased risk of suicide death. People having underlying diseases or living in metropolitan areas may be more susceptible to high air pollution exposure.