Leukocyte Traits and Exposure to Ambient Particulate Matter Air Pollution in the Women’s Health Initiative and Atherosclerosis Risk in Communities Study

BACKGROUND: Inflammatory effects of ambient particulate matter (PM) air pollution exposures may underlie PM-related increases in cardiovascular disease risk and mortality, although evidence of PM-associated leukocytosis is inconsistent and largely based on small, cross-sectional, and/or unrepresentative study populations. OBJECTIVES: Our objective was to estimate PM–leukocyte associations among U.S. women and men in the Women’s Health Initiative and Atherosclerosis Risk in Communities study ([Formula: see text]). METHODS: We based the PM–leukocyte estimations on up to four study visits per participant, at which peripheral blood leukocytes and geocoded address-specific concentrations of [Formula: see text] , [Formula: see text] , and [Formula: see text] in diameter ([Formula: see text] , [Formula: see text] , and [Formula: see text] , respectively) were available. We multiply imputed missing data using chained equations and estimated PM–leukocyte count associations over daily to yearly PM exposure averaging periods using center-specific, linear, mixed, longitudinal models weighted for attrition and adjusted for sociodemographic, behavioral, meteorological, and geographic covariates. In a subset of participants with available data ([Formula: see text]), we also estimated PM–leukocyte proportion associations in compositional data analyses. RESULTS: We found a [Formula: see text] (95% confidence interval: [Formula: see text] , 33) higher leukocyte count, a 1.2% (0.6%, 1.8%) higher granulocyte proportion, and a [Formula: see text] ([Formula: see text] , [Formula: see text]) lower [Formula: see text] T-cell proportion per [Formula: see text] increase in 1-month mean [Formula: see text]. However, shorter-duration [Formula: see text] exposures were inversely and only modestly associated with leukocyte count. DISCUSSION: The [Formula: see text] –leukocyte estimates, albeit imprecise, suggest that among racially, ethnically, and environmentally diverse U.S. populations, sustained, ambient exposure to fine PM may induce subclinical, but epidemiologically important, inflammatory effects. https://doi.org/10.1289/EHP5360