Association of road traffic noise exposure with dementia or cognitive impairment - A systematic review of longitudinal cohort studies.

Road traffic noise is a major public health concern associated with cardiometabolic outcomes, sleep disturbances, noise annoyance, and cognitive effects. Dementia poses a significant health and socioeconomic burden. While previous reviews have examined environmental noise broadly, few have synthesised longitudinal evidence on road traffic noise and dementia or cognitive impairment. This review evaluates this association using clearly defined inclusion criteria focused on cohort study designs. MEDLINE, EMBASE, CINAHL Plus and GreenFile were searched for studies on road traffic noise exposure and the risk of dementia or cognitive impairment among adults from inception to July 2025 without restrictions on setting or geographical location. Longitudinal cohort studies were identified using strict inclusion and exclusion criteria. Two independent reviewers conducted screening, data extraction, and quality assessment. A narrative synthesis was conducted. 3296 studies were retrieved from the searches, of which 3264 were excluded and 32 underwent full text screening. 8 studies were narratively synthesised. Risk of bias assessment using the ROBINS-E tool indicated that most studies were judged to have 'some concerns', with one study assessed as high risk and one as low risk of bias. The findings suggest that adults exposed to high levels of road traffic noise, particularly >50 dB, compared to those exposed to lower levels, are at higher risk of developing dementia or cognitive impairment. Current evidence from longitudinal cohort studies suggests a modest, directionally consistent association between road traffic noise and dementia or cognitive impairment, though effect sizes were generally small and often not statistically significant. While heterogeneity in methods precluded meta-analysis, convergence of findings across large cohorts supports further investigation using robust longitudinal designs. From a public health perspective, mitigating night-time traffic noise may offer co-benefits for cognitive health, sleep, and cardiovascular outcomes, and should be considered in urban planning and noise regulation.