Precision residential greenspace and dementia incidence in an urban Swedish cohort of older adults with 16 years follow-up and assessment of urban environment exposures and individual factors

Background: Increasing evidence suggests residential greenspace is beneficial for mental and cardiometabolic health. However, longitudinal studies on detailed residential greenspace and dementia incidence are yet limited, which this study examines, along with potential modifying effects of air pollution, road traffic noise, blue space, age, sex, and genetic risk profile in terms of carrying the APOE ε4 allele. Methods: Data were collected in the Swedish National Study of Aging and Care Kungsholmen and included 2993 dementia-free participants (mean age 73.1 years [±10.4 SD]) followed-up for 16 years, during which 477 (16%) developed clinically diagnosed dementia. Residential greenspace was assessed using satellite-derived Normalized Difference Vegetation Index (NDVI) within 100m, 250m, and 500m buffers. Hazard ratios (HR) and 95% confidence intervals (CI) of dementia incidence per interquartile range (IQR) increase in greenspace were estimated using Cox regression. Effect modifications of air pollution, blue space access, road traffic noise, age, sex and APOE-ε4 were tested through interaction terms (evaluated at p<0.1).Results: Per IQR (=0.18) increment in greenspace within a 100m buffer zone was associated with around 20% reduced hazard of dementia (HR 0.79 [CI 0.64, 0.96]). Associations were attenuated and statistically nonsignificant for larger buffers. The beneficial effect of greenspace on dementia incidence was stronger among female (HR 0.69 [CI 0.54, 0.89], p interaction=0.082) than male participants (HR 0.93 [CI 0.71, 1.24]). Other modifier interactions were statistically nonsignificant.Conclusions: Our findings suggest that greenspace in the close surrounding of the home may decrease the risk of developing dementia among older adults, especially women.