Streetview greenspace types and dementia risk in older adults: The Multi-Ethnic Study of Atherosclerosis.

BACKGROUND: Greenspace has been associated with lower dementia risk but most studies have used satellite-derived measures that cannot distinguish vegetation types. We used Street View-based metrics of greenspace from an on-the-ground perspective to examine greenspace types that may be relevant for dementia risk. METHODS: We followed 6761 participants from the Multi-Ethnic Study of Atherosclerosis, 2000-2018. Using deep learning algorithms applied to streetview images, we measured %trees, %grass, %other green (plants/flowers/fields) in the 500 m area around participants' residences. We examined the controlled direct effect of greenspace with dementia accounting for death as a censoring event, using a weighted Kaplan-Meier survival estimator, with the product of exposure weights and inverse-probability-of-censoring by death. We ran models separately per greenspace type. RESULTS: Mean baseline age was 62 (SD 10). Participants exposed to lowest levels of %Trees were more likely to have a household income < $24 999. We observed 585 (8·7%) dementia cases and 1437 (21·3%) deaths over follow-up. We observed a direct effect of high exposure to %grass on 19-year dementia risk had death been prevented of -4·57 (95% confidence interval:-8·15,-0·40) percentage points. No associations were observed for %trees (-0·07; 95%CI:-2·29,2·11) and %other green (-0·03, 95%CI:-1·59,1·48). CONCLUSION: Higher percentage of grass may reduce dementia risk.