Risk of incident myocardial infarction by gender: Interactions with serum lipids, blood pressure and smoking. The Tromsø Study 1979-2012

Background and aims: Overall, men have roughly twice the risk of myocardial infarction (MI) compared to women, but what causes this contrast is unclear. Identification of subgroups where the gender contrast in risk is particularly low or high, may provide new insight. In the search for such subgroups, we focus on gender-specific effects of established coronary heart disease (CHD) risk factors. Heterogeneity across age groups is also explored. Methods: Population-based prospective study from Tromsø, Norway, comprising 33,859 individuals (51% women); 2746 individuals (854 women) received a diagnosis of MI during follow-up at ages 35–94 years. Incidence rate ratios (IRR) were calculated as estimates of relative risk in Poisson regression analyses. Results: The association between total cholesterol and risk of MI was stronger for men than women, and IRR for men vs. women accordingly increased with increasing cholesterol, but the risk was higher for men in all subgroups (IRR in range 1.63–3.27), except among older people with low cholesterol levels. The adverse effect of increasing blood pressure (BP) was stronger for women, and IRR for gender diminished with increasing systolic (from 3.90 to 1.38) and diastolic BP (from 2.87 to 1.54). The gender contrast in risk was also substantially reduced in smokers ≥75 years. Associations with high-density lipoprotein cholesterol (HDL-C) did not differ between genders. Conclusions: Gender heterogeneity in associations with total cholesterol but not HDL-C indicates gender differences in associations with non-HDL-C. The stronger association with BP in women may relate to more severe hypertension-induced left ventricular hypertrophy.