Traffic‐related air pollution, lipoproteins, and cardiovascular disease risk in the VITamin D and OmegA‐3 TriaL (VITAL)

This project will leverage an existing randomized control trial of older individuals in the United States to examine the associations of exposure to traffic-related air pollution and incident cardiovascular disease events and biomarkers of cardiovascular health. The investigators will also explore the potential for vitamin D and omega-fatty acid supplementation to modify the associations.

Background and objectives: Multiple pathways have linked air pollution with cardiovascular disease (CVD), the leading cause of death in the U.S. and globally. We are examining both cross-sectional and longitudinal associations of traffic related air pollution (TRAP) with incident CVD (including coronary heart disease [CHD] and stroke) events and exploring potential mediating lipid pathways of risk in the study population of the VITamin D and OmegA-3 TriaL (VITAL), a double-blind, placebo-controlled clinical trial of vitamin D and marine omega-3 fatty acid supplements in the primary prevention of cancer and CVD.

Methods and approach: We use satellite-based small-scale (≤1 km) exposure models to estimate daily residence-specific ambient nitrogen dioxide (NO₂), particulate matter <2.5 µm (PM_2.5), and 11 tailpipe and non-tailpipe source PM_2.5 components. Cox proportional hazards models, stratified by sex, age, and randomization year, are fitted to estimate associations of long-term exposure with CVD outcomes. Results are presented as hazard ratios (HR) per interquartile (IQR) increase in exposure, adjusted for BMI and smoking.

Results and findings: During follow-up (5 years of intervention plus 6 years post-intervention, ongoing), a total of 2,314 CVD events occurred (1,111 CHD and 523 strokes) among 25,747 study participants with residence in the contiguous U.S. (50.6 % women, 69.7 % White, 19.8 % Black, mean baseline age 67.1 yrs). Average annual exposure before randomization was 19.6 ppb NO² and 9.0 µg/m3 PM_2.5.
NO² and total PM_2.5 mass were not associated with CVD or CHD. By contrast, PM_2.5 components calcium (Ca), potassium (K), and silicon (Si) were associated with increased risk of CHD (Ca: HR=1.08 [1.03-1.14]; K: HR=1.10 [1.03-1.17]; Si: HR=1.07 [1.02-1.14]). Associations with total CVD had a similar pattern but were weaker.

Conclusions and interpretations: Exposure to several markers for local non-tailpipe traffic was associated with increased long-term risk of CHD and CVD in the VITAL study population.