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

Research Article

Austin J Public Health Epidemiol. 2021; 8(2): 1097.

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

Woo KS1*, Timothy KCY1, Chook P1,2, Hu YJ3, Yin YH4, Lin CQ5, Lau KHA5, Lee PWA1 and Celermajer DS6

1Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Hong Kong SAR

2Institute of Chinese Medicine, The Chinese University of Hong Kong, Hong Kong SAR

3Nineth Peoples’ Hospital of Chongqing, China

4Second Hospital of Chongqing Medical University, China

5Department of Civil and Environment and Engineering, Hong Kong University of Science and Technology, Hong Kong SAR

6Faculty of Medical and Health Science, The University of Sydney, Sydney, Australia

*Corresponding author: KS Woo, Department of Medicine & Therapeutics, Tsang Shiu Tim Building, United College, The Chinese University of Hong Kong, Shatin NT, Hong Kong SAR

Received: April 24, 2021; Accepted: May 13, 2021; Published: May 20, 2021


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.

Keywords: Flow-mediated dilation; Carotid intima-media thickness; Air pollution (PM2.5); Metabolic Syndrome; Modernizing China


AP: Air Pollution; CVD: Cardiovascular Disease; CVS: Cardiovascular System; DBP: Diastolic Blood Pressure; FMD: Flow-Mediated Dilation; GTN: Glyceryltrinitrate Dilation; HDL-C: High Density Lipoprotein Cholesterol; IDF: International Diabetic Federation; IMT: Intima-Media Thickness; LDL-C: Low Density Lipoprotein Cholesterol; MS: Metabolic Syndrome; PM2.5: Particulate Matters <2.5 Microns in Diameter; SBP: Systolic Blood Pressure; TG: Triglycerides; WHO: World Health Organization


Cardiovascular Disease (CVD) is the leading cause of mortality and morbidity worldwide [1]. Each year over 400 million of new CVD cases are identified, accounting for 1.8 million deaths from CVD. Of the 7 million premature deaths each year linked to air pollution, 34% are related to ischemic heart disease, 21% to respiratory disease and 20% due to stroke [2,3]. A number of traditional risk factors have been implicated, including modifiable and non-modifiable factors. In addition, there is emerging evidence showing that small particulate matters (PM2.5) air pollution and Metabolic Syndrome (MS) are important novel risk factors, for the development of atherosclerosis [4-8].

It is now possible to assess early atherogenic process more objectively and noninvasively by ultrasonography. Both flowmediated dilation (FMD) and carotid Intima-media thickness (IMT) have been shown to be reliable and reproducible atherosclerotic surrogates, significantly correlated with endothelial physiology, severity and extent of coronary artery disease, and predictive of subsequent stroke and coronary events [9,10].

PM2.5 air pollution exposure has been associated with arterial endothelial dysfunction, intima-media thickening as well as computer tomography-derived coronary calcification [10-14]. MS is highly prevalent in the USA and most western countries (22-43.3%) [15,16]. The prevalence of MS in Chinese populations is comparatively lower (5.3-15%), but has been increasing in recent years, being higher in male versus female, and in urban versus rural areas [17,18]. We have previously reported a higher prevalence of MS among ex-farmers (43.2%), compared with farming residents in 3-Gorges Territories [19].

MS is associated will insulin resistance, diabetes mellitus, stroke and CVD [20]. In China, many rural Chinese are undergoing rapid economic transition and modernization, with increasing prevalence of atherosclerotic disease. We therefore proposed a study to evaluate the impact of PM2.5 air pollution and metabolic syndrome, as well as their interaction if any, on atherogenesis in modernizing China.

Subjects and Methods

In our Chinese Atherosclerotic Study in the Aged and Young (CATHAY Study), 1557 Han Chinese adults (aged 47.2±11.8 yrs, male 47%) in Hong Kong, Macau, Pan Yu, Yu County (Shanxi coal mine area), and 3-Gorges Territories of Yangtze River (Wu Shan, Da Cheong, Fuling and Kai County) were studied. The project protocol and previous findings have been outlined and published previously [21-24]. All subjects recruited were asymptomatic and apparently healthy. They were not known to have MS or more than 2 MS components, had no known major vascular, hepatic or renal diseases, and were not taking any regular medications or vitamin supplements.

After fasting for 14 hours and providing written informed consent, their CVD profiles (smoking status, body mass index, BMI, waist circumference and waist-hip ratio WHR, systolic and diastolic pressure SBP, DBP) were evaluated. Blood was taken for lipid profiles (high-density cholesterol HDL-C, low-density cholesterol LDL-C, and triglycerides TG) and fasting glucose. Ultrasonic scan of brachial and carotid arteries were performed. Bloods were assayed in batches at the Hospital Central Conde de Januarie, Macau, the Prince of Wales Hospital, Hong Kong and the Second Hospital of Chongqing Medical University, all currently accredited by the USA laboratory centers.

Metabolic Syndrome (MS) was diagnosed during screening (Figure 1A and 1B) according to International Diabetes Federation (IDF) criteria, with lower threshold of central obesity, HDL-C, TG and SBP, compared with other criteria [19,25,26].