Smoking, Serum Lipids, Blood Pressure, and Sex Differences in Myocardial Infarction

BACKGROUND: Few epidemiological studies have investigated the relative importance of major coronary risk factors in the two sexes within the same study population. In particular, it is not clear whether smoking carries a similar risk of coronary heart disease in men and women. METHODS AND RESULTS: The associations between smoking, serum lipids, blood pressure, and myocardial infarction were examined in a population-based prospective study of 11,843 men and women aged 35 to 52 years at entry. During 12 years, 495 cases of first myocardial infarction among men and 103 cases among women were identified. Myocardial infarction incidence was 4.6 times higher among men. The incidence was increased sixfold in women and threefold in men who smoked at least 20 cigarettes per day compared with never-smokers, and the rate in female heavy smokers exceeded that of never-smoking men. Multivariate analysis identified current smoking as a stronger risk factor in women (relative risk, 3.3; 95% confidence interval CI, 2.1 to 5.1) than in men (relative risk, 1.9; 95% CI, 1.6 to 2.3). Among those under 45 years old at entry, the smoking-related sex difference was more pronounced (in women: relative risk, 7.1; 95% CI, 2.6 to 19.1) (in men: relative risk, 2.3; 95% CI, 1.6 to 3.2). Serum total cholesterol, HDL cholesterol, and systolic blood pressure were also highly significant predictors in both sexes. CONCLUSIONS: Smoking was a stronger risk factor for myocardial infarction in middle-aged women than in men. Relative risks associated with serum lipids and blood pressure were similar despite large sex differences in myocardial infarction incidence rates.