Smoking cessation and carotid atherosclerosis : the Guangzhou Biobank Cohort Study d CVD

Introduction Smoking has been shown to be associated with carotid atherosclerosis in cross-sectional and prospective studies in Western populations. However, few studies have examined the reversal of risk resulting from quitting smoking, and the results are conflicting. Methods 959 men aged 50e85 years were randomly selected from phase III (2006e2007) of the Guangzhou Biobank Cohort Study into this cross-sectional study. Common carotid artery intima-media thickness (CCAIMT) was measured by B-mode ultrasonography, and carotid artery plaques were identified. Major cardiovascular risk factors, including fasting triglyceride, low-density and high-density lipoprotein (LDL and HDL) cholesterol and glucose, and systolic and diastolic blood pressure, were assessed. Results CCA-IMT and the number of carotid plaque increased from never to former to current smokers (both p#0.001). Among former smokers compared to current smokers, after adjustment for cigarette pack-years and other potential confounders, the adjusted ORs (95% CI) for quitting for 1e9, 10e19 and 20+ years were 0.77 (0.47 to 1.26), 0.45 (0.26 to 0.79) and 0.37 (0.17 to 0.77) for the presence of CCA atherosclerosis, and 0.69 (0.43 to 1.12), 0.47 (0.27 to 0.82) and 0.45 (0.23 to 0.96) for the presence of carotid plaques, respectively. Longer duration of quitting smoking was also significantly associated with decreasing risk of the severity of CCA atherosclerosis and carotid plaques (all p#0.001). Conclusion Smoking cessation was beneficial in attenuating the risk of carotid atherosclerosis associated with cigarette smoking. The short duration of cessation in earlier studies is a likely explanation for the inconsistent results. INTRODUCTION China is the world’s largest tobacco producer and consumer. Data from the 1996 National Prevalence Survey showed that about 30% of the world’s cigarettes were consumed by China’s 350 million smokers. In 2002, the prevalence of current smoking was 66% inmen and 3.1% inwomen aged 15 years or older. Data from phase I (2003e2004) of the Guangzhou Biobank Cohort Study (GBCS) showed that the prevalence of ever smokers in older Chinese people aged 50 years or abovewas 57.7% and 5.3% in men and women, respectively. Likewise, China has more attributable tobacco-related deaths than any other country. There remains comparatively low awareness of the smoking-related risk of cardiovascular disease among healthcare professionals and the public. Studies of the health effects, including the beneficial effects associated with quitting, within Chinese populations remain limited, yet such specific data should be of great importance in increasing awareness and changing population smoking habits. Carotid artery plaques and intima-media thickness (IMT), as measured by B-mode ultrasonography, are non-invasive quantitative measures of the presence and severity of carotid atherosclerosis. Carotid IMT has been associated with cardiovascular risk factors as well as cardiovascular events in cumulative studies, and has been wellaccepted as a marker of subclinical atherosclerosis. However, the results are not very robust as most of these studies were in hospitalized patients and the effect of underlying diseases on IMT finding was not examined. Methodological differences in the details of ultrasound examinations, such as the use of maximal or mean IMT or the measurement of near or far wall IMT, could affect the results. Furthermore, some studies have small sample size, which resulted in imprecise estimates of the risk. Cross-sectionally, carotid atherosclerosis (thicker IMT or plaques) is associated with major cardiovascular risk factors such as total cholesterol, lowdensity lipoprotein (LDL) cholesterol, fasting plasma glucose, systolic and diastolic blood pressure, and inversely with high-density lipoprotein (HDL) cholesterol. Prospectively, these surrogate markers predict increased risk of cardiovascular disease, such as myocardial infarction, coronary heart disease and stroke. Smoking has been shown to be associated with carotid atherosclerosis in cross-sectional 15 16 and prospective studies 18 in Western populations. However, few studies have examined the reversal of risk resulting from quitting smoking, and the results are conflicting. 19 20 Similarly, only two cross-sectional studies describing Chinese subjects can be found in the literature. A study from Taiwan found that age, systolic blood pressure and fasting blood glucose were independent risk factors for carotid IMT and plaques, but smoking was not. Thomas et al included Chinese from Hong Kong, Macau, San Francisco and China, and found that smoking was associated with adverse levels of the vascular disease surrogate markers, IMT and endothelial function. Neither of the above-mentioned studies examined risk reversal from quitting. Interventional studies showed that smoking cessation, as one lifestyle modification, can slow the progression of coronary atherosclerosis. However, whether lifestyle intervention such as smoking cessation can reverse the progression of carotid atherosclerosis is still controversial. 27 We present here the first report in a Chinese population exploring thedoseeresponse relationships Molecular Epidemiology Research Centre, Guangzhou Number 12 Hospital, Guangzhou, China Department of Community Medicine, School of Public Health, University of Hong Kong, Hong Kong SAR, China Department of Public Health and Epidemiology, University of Birmingham, Birmingham, UK Correspondence to Professor Tai Hing Lam, Department of Community Medicine, School of Public Health, The University of Hong Kong, Hong Kong, China; hrmrlth@hkucc.hku. hk Accepted 23 September 2009 Published Online First 12 October 2009 1004 J Epidemiol Community Health 2010;64:1004e1009. doi:10.1136/jech.2009. 092718 Research report