Impact of Tobacco Smoking and Smoking Cessation on Cardiovascular Risk and Disease

Christopher Bullen

Disclosures

Expert Rev Cardiovasc Ther. 2008;6(6):883-895. 

In This Article

Association Between Smoking & Cardiovascular disease

The association between smoking and cardiovascular disease was first elucidated in large epidemiological studies, in particular the British Doctors Study[5] and the Framingham Heart Study.[6] Although not given as much prominence as respiratory diseases at the time, smoking and its relationship to cardiovascular disease was one of the first topics addressed in the US Surgeon General's reports.[7] Subsequently, a large number of other epidemiological, clinical and laboratory studies in a range of settings among different population groups have provided consistent and compelling evidence of the leading role of tobacco smoking in the genesis of both acute cardiovascular events and atherosclerotic disease. In this section we review current epidemiological and pathophysiological evidence linking smoking with cardiovascular disease.

Epidemiology

Smoking has a greater impact on acute, typically thrombotic, events than on atherogenesis.[8] This is most marked in young and middle-aged adults, where smoking is responsible for approximately 50% of premature acute myocardial infarctions (AMIs).[8] The relative risk (RR) of cardiovascular events is much greater in younger than in older smokers[9] principally because such events are extremely rare in young nonsmokers. In the INTERHEART study, a multicenter, case–control study conducted in more than 50 countries, Teo et al. compared 12,133 cases of first AMI with 14,435 age- and sex-matched controls, and found that the effect of current smoking was significantly greater in younger (odds ratio [OR]: 3.53; 95% confidence interval [CI]: 3.23–3.86) than in older participants (OR: 2.55; 95% CI: 2.35–2.76) and was especially marked in younger subjects who smoked 20 cigarettes or more per day, in whom ORs were 5.6 (95% CI: 5.1–6.2).[9] However, the absolute excess mortality caused by smoking rises progressively with age.[10]

Among people with an AMI, smokers have better short-term survival, a phenomenon known as the ‘smoker's paradox' that exists presumably because these patients are younger, with few other risk factors and therefore with healthier coronary vessels than older nonsmokers.[11] While this unique combination of a greater propensity to acute thrombosis with less extensive atherosclerosis may confer a survival advantage over nonsmokers, smokers have worse outcomes than nonsmokers in other less acute coronary settings, such as after bypass surgery.

Tobacco smoking interacts in a multiplicative manner with the other major cardiovascular risk factors. When smoking is present with another risk factor, a higher risk generally results than would have resulted from simply adding together the independent risks.[11] For example, in a recent pooled analysis of 41 cohort studies involving over half a million participants (82% of whom were Asian), Nakamura and colleagues demonstrated that smoking significantly exacerbated the contribution of systolic blood pressure to the risk of hemorrhagic stroke. However, this was not found to be the case for ischemic stroke or coronary heart disease.[12]

In general, cardiovascular risks increase with the number of cigarettes smoked each day,[10,13] but the relationship is not straightforward. First, the measure of exposure widely used in studies – cigarettes per day – is of questionable validity. Smokers may smoke fewer cigarettes yet, in order to maintain their plasma nicotine level, may inhale more deeply, thereby increasing their exposure to harmful tobacco smoke toxins. Second, the type of tobacco product may misrepresent exposure. For example, ‘low tar' and ‘low nicotine' cigarettes are smoked differently from regular cigarettes[14] and, while cigar smoke contains the same toxins found in cigarette smoke, cigar smokers tend not to inhale.[15,16] Third, the association of smoking with cardiovascular risk is nonlinear. Smoking at very low levels of exposure (as low as 1–4 cigarettes per day) confers an almost threefold higher risk of dying from coronary heart disease compared with not smoking.[13,17,18] From five or more cigarettes per day the gradient of the exposure–risk curve is far less steep.[19]

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