Academic journal article Environmental Health Perspectives

Long-Term Exposure to Black Carbon and Carotid Intima-Media Thickness: The Normative Aging Study

Academic journal article Environmental Health Perspectives

Long-Term Exposure to Black Carbon and Carotid Intima-Media Thickness: The Normative Aging Study

Article excerpt

Introduction

Exposure to particulate air pollution has been associated with cardiovascular morbidity and mortality in numerous epidemiologic studies (Brook 2004; Brook et al. 2010; Dockery et al. 1993; Pope and Dockery 2006). Evidence suggests that local traffic is a major source of within-city heterogeneity in air pollution exposures (Brugge et al. 2007; Clougherty et al. 2008) and that mobile sources of pollution may be an important contributor to adverse health effects (Kunzli et al. 2000; Laden 2000; Peters et al. 2004). Several studies focusing specifically on the traffic-related constituents of pollution have reported short-term associations with indicators of cardiovascular health (Delfino et al. 2010a, 2010b; Madrigano et al. 2010; Mordukhovich et al. 2009). Evidence for long-term effects of chronic exposure to traffic-related air pollution has come largely from animal studies, which have demonstrated proatherosclerotic effects of diesel exhaust particles and concentrated ambient urban particles (Chen and Nadziejko 2005; Quan et al. 2010; Sun 2005). Recently, a growing number of epidemiologic studies have also observed associations between subclinical atherosclerosis and estimated fine particulate matter (particulate matter [less than or equal to] 2.5 um in aerodynamic diameter; [PM.sub.2.5]) or distance to major roadway (Bauer et al. 2010; Diez Roux et al. 2008; Hoffmann et al. 2007; Kunzli et al. 2005).

Black carbon is a correlate of traffic-related combustion products, and a common surrogate for traffic particles in general, weighted toward diesel particles. We have developed a nonlinear land use regression model to estimate black carbon exposures and have applied it within the greater Boston, Massachusetts, metropolitan area (Gryparis et al. 2007). In the present study making use of up to three repeated carotid intima-media thickness (CIMT) measures in a cohort of elderly men, we hypothesized that the estimated annual average concentration of black carbon at participants' homes in the year before the first study visit would be associated with CIMT, a reliable measure of subclinical atherosclerosis (Kanters et al. 1997; O'Leary and Bots 2010) that predicts cardiovascular outcomes (Nambi et al. 2012; O'Leary et al. 1999). In secondary descriptive analyses, we also estimated associations with residential proximity to a major roadway [defined as U.S. Census feature Class Code A1 (Primary Highway with Limited Access) or A2 (Primary Highway Without Limited Access)] and with average daily traffic within 100 m of residence.

Methods

Study population. The Normative Aging Study is a cohort of community-dwelling men from the greater Boston area recruited in the early 1960s. CIMT was measured in a subsample of participants beginning in 2004, after participants had been followed for four decades. Participants in the CIMT substudy were followed for up to three time points scheduled 1.5 years apart. Our analysis included 380 participants with complete information regarding black carbon concentrations and all covariates at baseline (i.e., the time of the first CIMT measurement). Baseline visits occurred between 2004 and 2008, and there were a total of 980 examinations between 2004 and 2010. All participants gave written informed consent prior to initiation of the study, and the study was approved by the institutional review boards of all participating institutions. A map of the region of participants' locations of residences is provided in Figure 1.

Physical parameters and medical history. Study center visits were subsquent to an overnight fast and abstention from smoking. Physical examinations included height and weight measurements, and body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared. We used questionnaires to evaluate smoking habits and medication use, with responses confirmed by an on-site physician. Alcohol intake (servings per day) was determined using the Cornell Medical Index (Brodman et al. …

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