Long-term exposure to outdoor air pollution and risk factors for cardiovascular disease within a cohort of older men in Perth

Abstract

While there is clear evidence that high levels of pollution are associated with increased all-cause mortality and cardiovascular mortality and morbidity, the biological mechanisms that would explain this association are less understood. We examined the association between long-term exposure to air pollutants and risk factors associated with cardiovascular disease. Air pollutant concentrations were estimated at place of residence for cohort members in the Western Australian Centre for Health and Ageing Health in Men Study. Blood samples and blood pressure measures were taken for a cohort of 4249 men aged 70 years and above between 2001 and 2004. We examined the association between 1-year average pollutant concentrations with blood pressure, cholesterol, triglycerides, C-reactive protein, and total homocysteine. Linear regression analyses were carried out, with adjustment for confounding, as well as an assessment of potential effect modification. The four pollutants examined were fine particulate matter, black carbon (BC), nitrogen dioxide, and nitrogen oxides. We found that a 2.25 μg/m3 higher exposure to fine particulate matter was associated with a 1.1 percent lower high-density cholesterol (95% confidence interval: -2.4 to 0.1) and 4.0 percent higher serum triglycerides (95% confidence interval: 1.5 to 6.6). Effect modification of these associations by diabetes history was apparent. We found no evidence of an association between any of the remaining risk factors or biomarkers with measures of outdoor air pollution. These findings indicate that long-term PM2.5 exposure is associated with elevated serum triglycerides and decreased HDL cholesterol. This requires further investigation to determine the reasons for this association.

Fig 1. Location of HIMAQs air monitoring sites, Perth, Western Australia, 2012.

Fig 2. Spatial distribution of modelled PM_2.5 for HIMS participants (wave II) across metropolitan Perth.

Fig 3. Effect sizes of the association between long-term exposure to air pollution and risk factors for cardiovascular disease, per IQR_w increase in air pollutant exposure under the main model.

Fig 4

Smoothed association between fine particulate matter (PM₂₅) and HDL cholesterol (top panel) and triglycerides (bottom panel) adjusted for the main confounders. Grey shade indicate the 95% confidence interval. Smoothed association estimated using a generalized additive model which included the same covariates as for the main model. Association is illustrated as the linear predictor of outcome for a typical cohort member and presented on the original scale of the outcome. That is, expected mean response for an individual with mean age, BMI, SEIFA, and lifestyle scores; never smoker, attended high school, and with no history of cvd or taking treatments to lower blood pressure or cholesterol; Note that the estimated association has the shape (only scaled up/down) for individuals with differing covariate values as the main model does not include interaction terms.

Fig 5. Effect modification of the association between long-term exposure to air pollution and risk factors for cardiovascular disease, per IQR_w increase in PM_2.5 exposure under the main model.