Cigarette smoking and the age at onset of a first non-fatal myocardial infarction

Background: Smoking is a major risk factor for coronary heart disease. Discontinuance of smoking is associated with a reduction in the risk of coronary disease; this risk approaches the level among non-smokers after stopping smoking for periods ranging from 6 months to several years. We analyzed pertinent prospectively accumulated data from our multicenter postinfarction studies to gain further insight into the complex relationship between cigarette smoking and the premature occurrence of a first myocardial infarction. Methods: Retrospective analysis of the relationship between the number of cigarettes smoked and the age at onset of patients experiencing their first non-fatal myocardial infarction was investigated in 2445 patients. The intensity of smoking was quantitated in terms of the average number of packs per day smoked during adult years, subcategorized in increments of a half-pack per day up to more than two packs per day. Ex- smokers were identified if they had stopped smoking 1 month before their index infarction. Analysis of variance was used to adjust for the effects of relevant confounding risk factors. Results: The adjusted age for first non- fatal infarction progressively declined with increasing smoking exposure, with an average age reduction of 8.7 years (95% confidence interval; 7.2, 10.2) in those smoking more than two packs per day compared with non-smokers. The graded effect was somewhat more marked in women than in men. The number of cigarettes smoked before infarction had no effect on the severity of the acute infarction or on mortality from cardiac causes during more than 2-year post-hospital follow-up. Those who stopped smoking 1 month or longer before the infarction were significantly older at the time of first infarction than active smokers in all smoking categories. Conclusion: This study provides strong evidence that active smoking is associated with an earlier age at onset of first infarctions, with a striking inverse dose-response effect. Stopping smoking appears to reduce the premature occurrence of coronary events.