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 (n=165,675). 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 PM <= 10, <= 2.5, and 2.5-10 mu m in diameter (PM10, PM2.5, and PM2.5-10, 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 (n=8,457), we also estimated PM-leukocyte proportion associations in compositional data analyses. RESULTS: We found a 12 cells/mu L (95% confidence interval: -9,33) higher leukocyte count, a 1.2% (0.6%, 1.8%) higher granulocyte proportion, and a -1.1% (-1.9%, -0.3%) lower CD8(+) T-cell proportion per 10-mu g/m(3) increase in 1-month mean PM2.5. However, shorter-duration PM10 exposures were inversely and only modestly associated with leukocyte count. DISCUSSION: The PM2.5-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.