Long-term exposure to air pollution and atherosclerosis in the carotid arteries in the Malmö diet and cancer cohort

Abstract

Background: Long-term exposure to air pollution increases the risk of cardiovascular morbidity and mortality, but the mechanisms are not fully known. Current evidence suggests that air pollution exposure contributes to the development of atherosclerosis. There are few studies investigating associations between air pollution and carotid plaques, a well-known precursor of cardiovascular disease.

Methods: A Swedish population-based cohort (aged 45-64 years at recruitment) was randomly selected from the Malmö Diet and Cancer study between 1991 and 1994, of which 6103 participants underwent ultrasound examination of the right carotid artery to determine carotid plaque presence and carotid intima media thickness (CIMT). Participants were assigned individual residential air pollution exposure (source-specific PM_2.5, PM₁₀, NO_x, BC) at recruitment from Gaussian dispersion models. Logistic and linear regression models, adjusted for potential confounders and cardiovascular risk factors, were used to investigate associations between air pollutants and prevalence of carotid plaques, and CIMT, respectively.

Results: The prevalence of carotid plaques was 35%. The mean levels of PM_2.5 and PM₁₀ at recruitment were 11 and 14 μg/m³, most of which was due to long range transport. The exposure contrast within the cohort was relatively low. PM_2.5 exposure was associated with carotid plaques in a model including age and sex only (OR 1.10 (95% CI 1.01-1.20) per 1 μg/m³), but after adjustment for cardiovascular risk factors and socioeconomic status (SES) the association was weak and not significant (OR 1.05 (95% CI 0.96-1.16) per 1 μg/m³). The pattern was similar for PM₁₀ and NO_x exposure. Associations between air pollutants and plaques were slightly stronger for long-term residents and in younger participants with hypertension. There was no clear linear trend between air pollution exposure and plaque prevalence. Non-significant slightly positive associations were seen between air pollution exposures and CIMT.

Conclusions: In this large, well-controlled cross-sectional study at low exposure levels we found no significant associations between air pollution exposures and subclinical atherosclerosis in the carotid arteries, after adjusting for cardiovascular risk factors and SES. Further epidemiological studies of air pollution and intermediate outcomes are needed to explain the link between air pollution and cardiovascular events.