Residential road traffic noise and incidence of depression in Denmark: a nationwide cohort study

Background Evidence linking transportation noise to depression is limited. We investigated associations between road traffic noise at the most (LdenMax) and least (LdenMin) exposed façades and depression risk in Denmark. Methods We established a nationwide cohort of 2,941,456 adults aged 25–65 years and for sensitivity analyses a nested questionnaire-based cohort, the Danish National Health Survey (DNHS, n=138,987). During follow-up from 2000 to 2017, 413,818 persons developed depression, defined as first hospital contact or ≥2 redeemed antidepressant prescriptions within one year. Road traffic noise (LdenMax and LdenMin) was estimated at all addresses and aggregated as 5-year means. Hazard ratios (HRs) were estimated using Cox models adjusted for individual and area-level socioeconomic factors, air pollution (PM 2.5 , NO 2 ), and green space. DNHS analyses were additionally adjusted for important lifestyle factors. Findings In fully adjusted models, HRs per interquartile range were 1.04 (95% confidence intervals 1.04, 1.05) for LdenMax and 1.07 (1.06, 1.07) for LdenMin. Splines indicated that regardless of LdenMax level, having ≥10 dB difference between LdenMax and LdenMin (reflecting the presence of a quieter side of the dwelling) was associated with lower risk. HRs were similar in DNHS with slight attenuations after lifestyle adjustment. Associations were higher among low socioeconomic groups, defined by low education, low income, and blue-collar work. Interpretation Long-term exposure to road traffic noise was associated with increased depression risk. Having a quiet façade mitigated this association, pointing to the importance of strategies prioritizing silent facades. Funding European Union and the Swiss State Secretariat for Education, Research and Innovation.