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 (PM₁₀ and PM_2.5) 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_2.5 and PM₁₀ exposure in all time periods were associated with smaller deep-gray brain volumes, but not other MRI markers. Higher PM_2.5 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_2.5 exposures were associated with smaller brain volumes in the Minnesota site. Further work is needed to understand the sources of heterogeneity across sites.