Risk of myocardial infarction by subgroups. All hazard ratio and 95% confidence intervals (HR, 95% CI) presented above are adjusted for age, residential area, income status, body mass index, fasting serum glucose, total cholesterol, blood pressure, alcohol consumption, physical activity, and the Charlson Comorbidity Index, and family history of myocardial infarction (where *P < 0.05, **P < 0.01, ***P < 0.001). Sustained smokers are the reference group for all HRs.