The association of long-term exposure to particulate matter air pollution with brain MRI findings: The ARIC study

BACKGROUND: Increasing evidence links higher particulate matter (PM) air pollution exposure to late-life cognitive impairment. However, few studies have considered associations between direct estimates of long-term past exposures and brain MRI findings indicative of neurodegeneration or cerebrovascular disease. OBJECTIVE: Our objective was to quantify the association between brain MRI findings and PM exposures approximately 5 to 20 y prior to MRI in the Atherosclerosis Risk in Communities (ARIC) study. METHODS: ARIC is based in four U.S. sites: Washington County, Maryland; Minneapolis suburbs, Minnesota; Forsyth County, North Carolina; and Jackson, Mississippi. A subset of ARIC participants underwent 3T brain MRI in 2011–2013 (n = 1,753). We estimated mean exposures to PM with an aerodynamic diameter less than 10 or 2.5 μm (PM and PM) in 1990–1998, 1999–2007, and 1990–2007 at the residential addresses of eligible participants with MRI data. We estimated site-specific associations between PM and brain MRI findings and used random-effect, inverse variance– weighted meta-analysis to combine them. RESULTS: In pooled analyses, higher mean PM and PM exposure in all time periods were associated with smaller deep-gray brain volumes, but not other MRI markers. Higher PM exposures were consistently associated with smaller total and regional brain volumes in Minnesota, but not elsewhere. CONCLUSIONS: Long-term past PM exposure in was not associated with markers of cerebrovascular disease. Higher long-term past PM exposures were associated with smaller deep-gray volumes overall, and higher PM exposures were associated with smaller brain volumes in the Minnesota site. Further work is needed to understand the sources of heterogeneity across sites.