Background: Although myocardial infarction (MI) is strongly related to smoking, few have studied why some smokers are more vulnerable than others. This study explored how the risk of MI in current and former smokers is modified by other cardiovascular risk factors.
Methods: Incidence of MI (fatal and nonfatal) amongst 10619 women, 48.3 +/- 8.2 years old, were studied in relation to smoking, hypertension, hypercholesterolaemia, diabetes, marital status and occupational level over a mean follow-up of 14 years.
Results: Of the 3738 smokers, one-third had at least one major biological risk factor besides smoking; 228 women had MI during follow-up. Smoking and hypertension showed a synergistic effect on incidence of MI. The adjusted relative risks (RR) were 12.2 (95% CI: 7.5-19.8) for smokers with hypertension, 5.3 (CI:3.3-8.1) for smokers with normal blood pressure and 2.4 (CI:1.4-4.3) for never-smokers with hypertension (reference: normotensive never-smokers). The corresponding RRs for diabetic smokers and diabetic never-smokers were 19.0 (CI: 10.2-35.4) and 8.8 (CI: 4.4-17.4), respectively (reference: nondiabetic never-smokers). In terms of attributable risks, hypertension, hypercholesterolaemia and diabetes accounted for 12.9, 11.5 and 7.2%, respectively, of MI in female smokers. Low socio-economic level and being unmarried accounted for 19.6 and 1.6%, respectively.
Conclusions: Although smoking is a major risk factor for MI, the risk varies widely between women with similar tobacco consumption. The results illustrate the need of a global risk factor assessment in female smokers and suggest that female smokers should be targets both for intensified risk factor management and programmes to stop smoking.