Abstract
OBJECTIVESCigarette smoking is an established, strong, and modifiable risk factor for coronary heart disease (CHD). However, little research has investigated CHD risk in former smokers who continue to be exposed to others’ cigarette smoke (former & secondhand smokers).METHODSIn the Tehran Lipid and Glucose Study, a prospective population-based cohort (n=20,069) was followed up for a median period of 14.6 years. A subset of 8,050 participants of 30 years of age and older was analyzed, with first CHD events as the study outcome. Participants were categorized as never, former, current, secondhand, and former & secondhand smokers. Data on smoking intensity (cigarette/d) were also collected. A Cox proportional hazards regression model was applied to estimate the risk of CHD, taking into account the main potential confounders.RESULTSThe mean age of participants was 46.10 ±11.38 years, and they experienced 1,118 first CHD events (with most CHD cases in former smokers) during the follow-up period. The risk of CHD was highest in current smokers, followed in order by former & secondhand, former, and secondhand smokers (hazard ratio [HR], 1.99; 95% confidence interval [CI], 1.65 to 2.39; HR, 1.55; 95% CI, 1.15 to 2.08; HR, 1.39; 95% CI, 1.12 to 1.72; HR, 1.27; 95% CI, 1.07 to 1.51, respectively), compared to never smokers. The risk of CHD increased with smoking intensity, which has been proposed as a preferable measure of smoking, indicating a dose-response pattern.CONCLUSIONSThe elevated risk of CHD in former & secondhand smokers was a noteworthy finding, with possible implications for health policy; however, further research is needed.
Highlights
Despite remarkable advances in the treatment of cardiovascular disease (CVD)—and in particular, coronary heart disease (CHD)— CVD and its clinical sequelae continue to be the leading cause of morbidity and mortality worldwide [1,2,3]
Fewer than 15% of the study population had a history of type 2 diabetes mellitus (T2DM) and both sexes were, on average, overweight
One-quarter of the participants reported a history of cigarette smoking (25.4%), of which 3.4% were females
Summary
Despite remarkable advances in the treatment of cardiovascular disease (CVD)—and in particular, coronary heart disease (CHD)— CVD and its clinical sequelae continue to be the leading cause of morbidity and mortality worldwide [1,2,3]. The prevalence of current smokers has decreased over time in several countries, the global absolute number of smokers has increased owing to population growth [8]. Several observational studies have focused on the associations between cigarette smoking and CVD, myocardial infarction (MI), CHD, and stroke [12,13,14,15]. Based on the Framingham cohort study findings, former heavy smokers have significantly elevated CVD risk extending beyond 5 years after cessation compared to never smokers [18]. A recently published systematic review and meta-analysis indicated that smoking only about 1 cigarette/d resulted in an additional risk of developing CHD and stroke that was much greater than expected [9]
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