Residential Proximity to Major Roadways, Fine Particulate Matter, and Hepatic Steatosis: The Framingham Heart Study

Abstract

We examined associations between ambient air pollution and hepatic steatosis among 2,513 participants from the Framingham (Massachusetts) Offspring Study and Third Generation Cohort who underwent a computed tomography scan (2002-2005), after excluding men who reported >21 drinks/week and women who reported >14 drinks/week. We calculated each participant's residential-based distance to a major roadway and used a spatiotemporal model to estimate the annual mean concentrations of fine particulate matter. Liver attenuation was measured by computed tomography, and liver-to-phantom ratio (LPR) was calculated. Lower values of LPR represent more liver fat. We estimated differences in continuous LPR using linear regression models and prevalence ratios for presence of hepatic steatosis (LPR ≤ 0.33) using generalized linear models, adjusting for demographics, individual and area-level measures of socioeconomic position, and clinical and lifestyle factors. Participants who lived 58 m (25th percentile) from major roadways had lower LPR (β = -0.003, 95% confidence interval: -0.006, -0.001) and higher prevalence of hepatic steatosis (prevalence ratio = 1.16, 95% confidence interval: 1.05, 1.28) than those who lived 416 m (75th percentile) away. The 2003 annual average fine particulate matter concentration was not associated with liver-fat measurements. Our findings suggest that living closer to major roadways was associated with more liver fat.

Keywords: air pollution; computed tomography; fine particulate matter; hepatic steatosis; liver fat.

Figure 1.

Histograms of 2003 annual average PM_2.5 concentrations (A), distance to major roadways (B), and liver-to-phantom ratio (C) in participants from the Multi-Detector Computed Tomography Study, Boston, Massachusetts, 2002–2005.

Figure 2.

Associations between distance to the nearest major roadway and the 25th, 50th, and 75th percentiles of the distribution of liver-to-phantom ratio in participants from the Multi-Detector Computed Tomography Study, Boston, Massachusetts, 2002–2005. Models adjusted for age at MDCT scan and (age at MDCT scan)², sex, cigarette-smoking status (current, former, or never), pack-years of smoking, alcohol intake, educational level, usual occupation, physical activity, antihypertensive medication use, statin use, quartile of median household income in the participant's census tract in 2000, median value of owner-occupied housing units in the census tract, population density (population/km²) in the census tract, cardiovascular disease, diabetes, and an exam identifier. Results were scaled to approximate comparing participants who lived 58 m from the nearest major roadway with those who lived 416 m from the nearest major roadway. Bars: 95% confidence intervals.