Do associations of neighbourhood attributes with cognitive function vary by socio-economic status? A 12-year follow-up study of older Australians.

Socio-economic status (SES), neighbourhood environments and their interactions can influence cognitive health in late life. Studies on this topic have examined a limited number of SES and environmental indicators and are mostly cross-sectional. We analysed data from 1160 individuals aged 60-64 years at baseline, with four assessments of cognitive functions across 12 years. SES indicators included education, homeownership, financial problems and area-level SES. Neighbourhood environmental attributes were determined using Geographic Information Systems (GIS) data on population and street intersection densities, commercial land, parkland, tree canopy cover, non-commercial land use mix, transit points, blue space and annual average PM and NO concentrations. Most GIS indicators were measured at two time points. We estimated the independent associations of SES indicators with multiple cognitive health outcomes and the moderating effects of SES indicators on environment-cognition associations. All SES indicators were related to cognitive health in the expected direction. Many environment-cognition associations were moderated by SES indicators. In general, more walkable neighbourhoods, characterised by better access to services, higher levels of street connectivity and a greater percentage of tree canopy cover were associated with better cognitive outcomes (levels or/and trajectories) in respondents with fewer years of education and/or reporting financial problems. Negative associations of population density and PM concentrations with cognitive outcomes were found in non-homeowners, while access to services appeared to be more beneficial to residents of high- than low-SES neighbourhoods. Walkable, treed, unpolluted neighbourhoods with good-quality affordable housing may contribute to a substantial reduction in SES inequalities in older adults' cognitive health.