Neighborhood environments and transition to cognitive states: Sydney Memory and Ageing Study.

Introduction: Features of the neighborhood environment and ambient air pollution have been associated with onset and progression of neurocognitive disorders, but data from longitudinal population-based studies are limited.

Methods: One thousand thirty-six participants (78.3 ± 4.8 years) of the Sydney Memory and Ageing Study were followed for up to 13.7 years with biennial cognitive assessments. Neighborhood environmental features were assessed around the participants' homes. Associations between environmental features and transitions to cognitive states were estimated.

Results: Population density, street connectivity, access to commercial services, public transport, water bodies, and tree canopy were associated with a lower likelihood of worsening cognitive state. The opposite was observed for annual average concentrations of PM. Access to parkland, blue spaces, and public transport were associated with a higher likelihood of reversal from mild cognitive impairment to normal cognition.

Discussion: Healthy neighborhood environments may delay cognitive decline and the onset of dementia in older individuals.

Highlights: This is the first published study on neighborhood built and natural environmental correlates of transition to dementia. This study was conducted in socially advantaged areas with relatively low ambient air pollution. Walkable neighborhoods are associated with a lower likelihood of worsening cognitive state. Neighborhood tree canopy is consistently predictive of better cognitive outcomes. Access to public transport, and blue and green spaces is associated with higher probability of improved cognitive state.