Smoking and Other Major Coronary Risk Factors and Acute Myocardial Infarction before 41 Years of Age: Two Danish Case-control Studies

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Abstract
Objective - The aim of two case-control studies of adults younger than 41 years of age was to assess how the major coronary risk factors, family history of acute myocardial infarction (AMI), obesity, hypertension and hypercholesterolemia add to the risk of AMI from self-reported current smoking (smoking). Design - An evaluation study included 35 patients and 70 individually matched controls. Results - The risk from smoking increased less than linearly and the risk from serum cholesterol concentration (cholesterol) increased linearly. In multiple conditional logistic regression analyses, smoking as a discrete variable and cholesterol as a continuous variable were significant coronary risk factors. In a final logistic regression model, the odds ratio was 6.4 (95% confidence interval (CI) 1.7-24.1) for smoking and 1.6 (CI 1.1-2.3) for each mmol/L cholesterol. A risk score summarizing the combined risk of the major coronary risk factors did not add to the final logistic regression model (p = 0.56). A validation study included 79 patients and 64 matching control patients. Conclusion - The major coronary risk factors were similar for the cases/patients and the two control groups in the two studies. Therefore, the final logistic regression model may reflect a general pattern in Denmark. Primary prevention in individuals less than 41 years of age should focus on smoking and cholesterol instead of the summarizing risk score.