IJE Advance Access originally published online on September 14, 2005
International Journal of Epidemiology 2005 34(5):1045-1046; doi:10.1093/ije/dyi165
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Commentary |
Commentary: Smoking and atherosclerotic diseases in Asia—the implication in global atherosclerosis prevention
Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Hong Kong SAR, People's Republic of China
* Corresponding author. Professor of Medicine and Therapeutics and Consultant Cardiologist, Prince of Wales Hospital, Shatin, Hong Kong SAR, People's Republic of China. E-mail: kamsangwoo{at}cuhk.edu.hk
Atherosclerotic disease including stroke and coronary artery disease (CAD) is the most important health issue of modern society. Cigarette smoking has been associated with this disease in Western countries.1 In comparison, the impact of smoking on cardiovascular health has been less well documented in Asia, and, in particular, its impact in China where the population at risk currently comes up to one-quarter of the global population is unclear. Interest in the impact of smoking in China is inspired by the fact that although 70% of Chinese males smoke (compared with current prevalence in the range 20–30% for men in most Western populations), the prevalence of CAD in Chinese men is one-quarter of that for Western men.2 Furthermore, there is evidence that young Chinese adults have less arterial endothelial dysfunction (a novel surrogate atherosclerosis marker predictive of cardiovascular outcome) than white adults with similar direct or indirect exposure to cigarette smoke.3 A second cross-sectional study, similarly using a surrogate marker of cardiovascular disease [carotid intima-media thickness (IMT)], found that Chinese adults who had Western lifestyles had thicker IMT than native rural Chinese, and that the detrimental effect of cigarette smoking on IMT was greater in Westernized Chinese living in Hong Kong and Sydney than it was in native rural Chinese.4 These differences suggest a relative protection of Chinese from the effect of cigarette smoking, possibly due to certain gene differences, which may be modified by Westernization, and subscribe to a gene–environment interaction process, or to an interaction between smoking, changes in lifestyles, and other risk factors in the process of Westernization. While evaluation of the underlying lifestyles, dietary habits, and subsequently physiological and biochemical changes related to such Westernization process are awaited with much interest, these early results call for further studies that examine and compare smoking-related effects in acculturated migrant Chinese population with those in village natives in mainland China.5
To illuminate this important health issue, the paper from the Asian Pacific Cohort Studies Collaboration in this issue of the journal6 addressed the problem from an epidemiological perspective. With the strength of large numbers of subjects (n = 562 338) and, therefore, more precise estimates, they confirmed that smoking is a risk factor for both coronary heart disease (CHD) and stroke, independent of the effects of BMI, blood pressure, and cholesterol, with the amelioration of the effects after quitting. Of much interest and importance, Asians and Caucasians (in Australia and New Zealand) had similar increased proportional cardiovascular risk (relative risk) from smoking cigarettes, and similar relative risk reduction from quitting. Moreover young people and women had greater relative risk of cardiovascular disease from smoking, but the effect declined with age. This report also appropriately documented relative and attributable risks for CHD and strokes in different groups. While there were no differences in their relative risk, the attributable risk for CHD from smoking reflected the prevalence of smoking in different groups and, hence, was higher in Chinese men (30%) compared with Australian (13%) and New Zealand men (7%) but was lower in Chinese women (3%) compared with the other two groups (11% for Australia and 6% for New Zealand). However, it should be noted that the overall absolute risk of CAD (fatal and non-fatal) in Australia and New Zealand (2.6%) is still higher than that in Asia (0.35%), possibly reflecting the effects of different genes and gene–environment interactions in the two regions. Time will tell whether these differences in absolute risk will converge and abolish, with the changing trend of smoking and modernization in the two regions.
The greater smoke-related impact on cardiovascular health of young women is of much public health concern, given that the tobacco epidemic is still spreading among women (estimated 530 million by 2025) and that, although prevalence rates are low in Asian women, the high rates in men mean that they are exposed to high levels of passive smoking. Tobacco control policies should, therefore, always include messages specifically targeted at women.
The strength of this paper is its large sample size. However, it is important to note that the present study is a retrospective overview 'meta-analysis' of 40 observational studies spreading over 37 years from 1961 to 1998, using non-uniform study protocols and data entries for smoking status and smoking (inhalation) habits. The types of cigarette smoked, changes in inhalation habits overtime and years of follow-up were not uniformly available. In addition, information on many important confounding factors, including body mass index, blood pressure, and cholesterol levels were missing in some of these cohorts, and the cholesterol assay understandably were carried out in different laboratories, using different methods and standardization, over a long period of 37 years. It may be quite difficult to interpret the validity of the statistical adjustment for these confounders in the Cox model assessment. Lastly, cigarette consumption and quitters were self-reported with no objective assessment (such as cotinine levels) of this self-report.
Nevertheless, the message from this large Asia-Pacific database is loud and clear. As one-third of all cigarettes are smoked in China alone, this paper underlines the observations made by previous authors that, if smoking goes unchecked, the impact of smoking upon health in Asia, and particularly in China, will be huge.
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1 Tunstall-Pedoe H. (ed.) MONICA Monograph and Multimedia Sourcebook. Geneva: WHO, 2003.
2 Wu Z, Yao C, Zhao D et al. Sino-MONICA project: a collaborative study on trends and determinants in cardiovascular diseases in China, Part I: morbidity and mortality monitoring. Circulation 2001; 103:462–68.
3 Woo KS, Robinson JTC, Chook P et al. The different effect of cigarette smoking on endothelial function in Chinese and Caucasian adults. Ann Intern Med 1997;127:372–75.
4 Woo KS, Chook P, Raitakari OT, McQuillan B, Celermajer DS. Westernization of Chinese adults and increased subclinical atherosclerosis. Arterioscler Thromb Vasc Biol 1999;19:2487–93.
5 Commentary. Smoke resistance in Asian arteries. Science 1999; 227:769.[CrossRef]
6 Asia Pacific Cohort Studies Collaboration: Smoking, quitting and the risk of cardiovascular disease amongst women and men in the Asia-Pacific region. Int J Epidemiol 2005;34:1036–45.
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