Sex differences in risk factors for myocardial infarction: cohort study of UK Biobank participants

Abstract

Objectives: To investigate sex differences in risk factors for incident myocardial infarction (MI) and whether they vary with age.

Design: Prospective population based study.

Setting: UK Biobank.

Participants: 471 998 participants (56% women; mean age 56.2) with no history of cardiovascular disease.

Main outcome measure: Incident (fatal and non-fatal) MI.

Results: 5081 participants (1463 (28.8%) of whom were women) had MI over seven years' mean follow-up, resulting in an incidence per 10 000 person years of 7.76 (95% confidence interval 7.37 to 8.16) for women and 24.35 (23.57 to 25.16) for men. Higher blood pressure indices, smoking intensity, body mass index, and the presence of diabetes were associated with an increased risk of MI in men and women, but associations were attenuated with age. In women, systolic blood pressure and hypertension, smoking status and intensity, and diabetes were associated with higher hazard ratios for MI compared with men: ratio of hazard ratios 1.09 (95% confidence interval 1.02 to 1.16) for systolic blood pressure, 1.55 (1.32 to 1.83) for current smoking, 2.91 (1.56 to 5.45) for type 1 diabetes, and 1.47 (1.16 to 1.87) for type 2 diabetes. There was no evidence that any of these ratios of hazard ratios decreased with age (P>0.2). With the exception of type 1 diabetes, the incidence of MI was higher in men than in women for all risk factors.

Conclusions: Although the incidence of MI was higher in men than in women, several risk factors were more strongly associated with MI in women compared with men. Sex specific associations between risk factors and MI declined with age, but, where it occurred, the higher relative risk in women remained. As the population ages and the prevalence of lifestyle associated risk factors increase, the incidence of MI in women will likely become more similar to that in men.

Fig 1

Adjusted hazard ratios for association between risk factors and incident myocardial infarction by sex. Horizontal lines indicate corresponding 95% confidence intervals around hazard ratios. All models were adjusted for age. Additionally, systolic blood pressure, diabetes, and socioeconomic status were adjusted for each other as well as smoking status, body mass index, lipid lowering drugs, and antihypertensive drugs. Atrial fibrillation was similarly adjusted for these eight variables. Diastolic blood pressure and American Heart Association hypertension stages were adjusted for the same variables as systolic blood pressure. Models for smoking variables included socioeconomic status, and models for body mass index contained smoking status and socioeconomic status

Fig 2

Adjusted women-to-men ratios of hazard ratios for association between risk factors and incident myocardial infarction. Horizontal lines indicate corresponding 95% confidence intervals around ratio of hazard ratios. All models were adjusted for age. Additionally, systolic blood pressure, diabetes, and socioeconomic status were adjusted for each other as well as smoking status, body mass index, lipid lowering drugs, and antihypertensive drugs. Atrial fibrillation was similarly adjusted for these eight variables. Diastolic blood pressure and American Heart Association hypertension stages were adjusted for the same variables as systolic blood pressure. Models for smoking variables included socioeconomic status, and models for body mass index contained smoking status and socioeconomic status

Fig 3

Adjusted hazard ratios for association between risk factors and incident myocardial infarction by age group and sex. Horizontal lines indicate corresponding 95% confidence intervals around hazard ratios. Systolic blood pressure is given per 20 mm Hg and diastolic blood pressure per 10 mm Hg. Participants with stage 2 hypertension were compared with participants with normal blood pressure; current smokers were compared with never smokers; participants with diabetes were compared with those without diabetes; obesity was compared with body mass index less than 25 kg/m²; and for socioeconomic status the lowest third was compared with the highest third. Models for systolic blood pressure, diabetes and socioeconomic status were adjusted for each other as well as smoking status, body mass index, lipid lowering drugs, and antihypertensive drugs. Diastolic blood pressure and American Heart Association hypertension stages were adjusted for the same variables as systolic blood pressure. Models for smoking variables included socioeconomic status, and models for body mass index contained smoking status and socioeconomic status

Fig 4

Adjusted women-to-men ratios of hazard ratios for association between risk factors and incident myocardial infarction by age group. Horizontal lines indicate corresponding 95% confidence intervals around ratio of hazard ratios. Systolic blood pressure is given per 20 mm Hg and diastolic blood pressure per 10 mm Hg. Participants with stage 2 hypertension were compared with participants with normal blood pressure; current smokers were compared with never smokers; participants with diabetes were compared with those without diabetes; obesity was compared with body mass index less than 25 kg/m²; and for socioeconomic status the lowest third was compared with the highest third. Models for systolic blood pressure, diabetes, and socioeconomic status were adjusted for each other as well as smoking status, body mass index, lipid lowering drugs, and antihypertensive drugs. Diastolic blood pressure and American Heart Association hypertension stages were adjusted for the same variables as systolic blood pressure. Models for smoking variables included socioeconomic status, and models for body mass index contained smoking status and socioeconomic status