Night noise exposure and risk of death by suicide in adults living in metropolitan areas

Background: Noise is defined as sound that is unwanted, unpleasant, or harmful to health. It may induce negative emotions and mental health problems and even may leads to increased suicide risk. Little attention has been paid so far to a potential link between noise and suicide. We investigated the association between nighttime environmental noise and suicide death in adults in the Republic of Korea. Methods: We analyzed the data from the National Health Insurance Service-National Sample Cohort, with a 4-year baseline (2002-2005) and an 8-year follow-up (2006-2013) assessment. A total of 155,492 adults constituted the study sample: younger adults (20-54 years, n = 124,994), or older adults (>= 55 years, n = 30,498), and adults with mood and anxiety disorders (n = 34,615). Suicide death was defined as per International Classification of Diseases-10 code X60-X84. Data on nighttime noise were obtained from the National Noise Information System. Results: During the study period, 315 (0.2%) died of suicide. The incidence of suicide per 100,000 person-years was 25.71. With interquartile range increases in nighttime noise, the adjusted hazard ratio (HR) for suicide death was significantly increased: 1.32 (95% confidence interval [CI]: 1.02-1.70) for younger adults, 1.43 (95% CI: 1.01-2.02) for older adults, and 1.55 (95% CI: 1.10-2.19) for adults with mental illness. In the penalized regression spline models, the HRs for suicide death were gradually increased with environmental noise levels, and the risk was the highest for adults with mental illness. Conclusions: We found a significant association between exposure to nighttime noise and the risk of suicide death in adults in the Republic of Korea.