Traffic exposure and subclinical cardiovascular disease: is the association modified by socioeconomic characteristics of individuals and neighbourhoods? Results from a multilevel study in an urban region

Objectives: Traffic-related pollution is associated with cardiovascular disease in general, but previous studies suggested that low socioeconomic status (SES) groups might be more susceptible towards a negative impact. We examined whether the association between long-term exposure to high traffic and early signs of coronary artery disease is modified by SES. Methods: Individual-level medical and social data from a population-based study were linked with census information on neighbourhood socioeconomic characteristics. Residential exposure to traffic was defined as proximity to major roads using a geographical information system. We studied associations between high traffic and coronary artery calcification (CAC) within strata of SES to examine effect modification. Data stem from an epidemiological study in Germany including 2264 women and 2037 men (45-75 years). Results: High traffic and low SES were both associated with higher amounts of calcification (>= 75th age-specific percentile). More participants with low SES lived close to major roads while stratified analyses did not indicate higher susceptibility in low SES groups. Participants with low SES and simultaneous exposure to high traffic had highest levels of CAC. For example, the prevalence of high calcification was 23.9% in better-educated men with low traffic exposure but 37.7% in lower-educated men with high traffic exposure (women: 22.0% vs 28.1%). Conclusions: High traffic exposure was associated with coronary calcification in all social groups, but as low SES individuals had higher calcification in general and were also more often exposed to traffic, existing inequalities could be further shaped by traffic exposure.