Mixtures of key components of the external exposome in association with MRI biomarkers of brain structure: Multi‐Ethnic Study of Atherosclerosis

INTRODUCTION: There is a critical need to identify risk factors of Alzheimer's disease and related dementias (ADRD). METHODS: We included 1227 participants (mean age [standard deviation]: 74.1 [7.9] years) from the Multi-Ethnic Study of Atherosclerosis with brain MRI scans. We investigated joint associations of 13 natural, social, and built-environment exposures with gray matter volume (GMV) (n = 1219), white matter fractional anisotropy (WM FA) (n = 1102), and white matter hyperintensity volume (n = 1210) using weighted quantile sum regression. RESULTS: A one-decile increase in all harmful exposures was associated with lower GMV and WM FA; however, associations were null when adjusting for study site. DISCUSSION: Examining the impact of many environmental factors simultaneously may provide insight into important modifiable risk factors for ADRD, capturing concomitant exposures as they are experienced.