Independent Effects of Metabolic Syndrome and Air Pollution (PM2.5) on Atherosclerosis in Modernizing China

Background: Air Pollution (AP) and metabolic syndrome (MS) are important global health hazards of the 21st century, in mainland China in particular, and AP has been associated with increased prevalence of cardiovascular diseases, and stroke. Methods: To evaluate the impact of metabolic syndrome on AP-related atherogenesis, 1557 Han Chinese adults (mean age 47.2±11.8 years, male 47%) in Hong Kong, Macau, Pun Yu, Yu County (Shanxi coalmine) and 3-Gorges (Yangtze River) were studied. Cardiovascular risk profiles and metabolic syndrome (IDF criteria) were evaluated. PM2.5 (satellite sensor modeling), and atherosclerotic surrogates, brachial reactivity (FMD) and carotid Intima-media thickness (IMT) (ultrasound), were measured. Results: The yearly PM2.5 concentration ranged from 34.0μg/m³ in Hong Kong to 93.8μg/m³ in 3-Gorges Territories. MS was diagnosed in 340 subjects (21.8%). Smoking status, gender and PM2.5 were similar in the MS cohort versus those without MS. Blood pressures (SBP and DBP), waist circumference, triglycerides and glucose were higher, but high-density lipidcholesterol was lower in the MS cohort, compared to the other subjects. Brachial FMD was significantly lower and carotid IMT significantly higher (0.70±0.13 mm, 95% CI 0.68-0.71 mm vs. 0.63mm±0.14mm, 95% CI 0.62-0.64 mm) in the MS cohort than those without (P<0.0001). On multivariate regression, PM2.5 was not related to MS development, but was significantly related to carotid IMT in both no MS (beta=0.234, P<0.0001) and MS cohorts (beta=0.245, p<0.0001), independent of age, SBP, and waist circumference. There was no direct interaction between PM2.5 and MS. Conclusions: Both AP and MS have independent impacts on atherogenic processes in China, with significant implications for atherosclerosis prevention.