Urban living and dementia risk: associations with perceived green space qualities and traffic noise annoyance

Dementia is a major public health concern, and ambient air pollution is increasingly recognized as a plausible risk factor. Green space and traffic noise have also been proposed as environmental determinants of dementia but have received less attention. We examined whether novel, perception-based measures of urban green space and traffic noise annoyance were associated with dementia risk. We included around 30,250 participants from the Malmö Diet and Cancer cohort, followed from 1991 to 2014. Neighborhood-level perceptions of serenity, wilderness, and species richness (Perceived Sensory Dimensions [PSDs]), as well as road and train noise annoyance, were derived from regional surveys and linked to participants' annual residential addresses. We also constructed a combined PSD index as the sum of z-scores. Time-varying Cox models were used to estimate associations with clinically validated all-cause dementia (ACD), Alzheimer's disease (AD), and vascular dementia (VaD), adjusting for demographic, lifestyle, and health factors. In sensitivity analyses, we additionally adjusted for air pollution. Higher neighborhood PSDs were associated with lower risks of ACD and AD (ACD: hazard ratio [HR] per interquartile range [IQR] increase in the PSD index, 0.94; 95% CI, 0.88–0.99). Road traffic noise annoyance was associated with a higher risk of ACD (HR, 1.07; 95% CI, 1.00–1.14), whereas train noise annoyance showed no clear association. Patterns for VaD were similar but less precise. Neighborhoods perceived as more serene, wild, and species-rich were associated with lower dementia risk, while greater road traffic noise annoyance was associated with higher risk. These findings support the relevance of the residential environment for dementia risk and highlight the value of perception-based exposure measures in environmental epidemiology.