Cigarette smoking in relation to the risk of myocardial infarction in young women. Modifying influence of age and predisposing factors.

We evaluated the relation between myocardial infarction (MI) and cigarette smoking in women 30 to 49 years of age. Among 318 women who had survived recent first infarctions and 1272 age-matched controls, the proportions of cigarette smokers were 83% and 54%, respectively (p < 0.001). The estimated relative risk rose progressively with amount smoked: compared with women who had never smoked, the estimate was 1.8 for smokers of less than 15 cigarettes per day and 6.9 for smokers of 35 or more cigarettes per day. At each level of smoking, the relative increase in risk was greater at younger ages and among those not apparently predisposed from other factors. Although MI is a rare disease in young women, our data indicate that the risks faced by those who smoke heavily are appreciable.