High blood pressure, smoking and diabetes increase the risk of heart attack in both sexes but they have more impact in women than they do in men, shows a study by researchers at The George Institute for Global Health, University of Oxford, Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, The George Institute for Global Health, University of New South Wales, Australia and the department of epidemiology, Johns Hopkins University. Overall, men are at greater risk of heart attack than women, but several studies have suggested that certain risk factors have more of an impact on the risk in women than in men.
To look more closely at this association, researchers looked at data on almost half a million people enrolled in the UK Biobank – a database of biological information from British adults. The 471,998 people had no history of cardiovascular disease, were aged 40 to 69 years and 56% of them were women.
Over an average of seven years, 5,081 people (29% of whom were women) had their first heart attack, meaning that the incidence of heart attack was 7.76 per 10,000-person years in women compared with 24.35 per 10,000-person years in men.
High blood pressure, diabetes and smoking increased the risk of a heart attack in both sexes but their impact was far greater in women. Smoking increased a woman’s risk of a heart attack by 55% more than it increased the risk in a man, while high blood pressure increased a woman’s risk of heart attack by an extra 83% relative to its effect in a man.
Type II diabetes, which is usually associated with poor diet and other lifestyle factors, had a 47% greater impact on the heart attack risk of a woman relative to a man, while type I diabetes had an almost three times greater impact in a woman.
The authors believe that theirs is the first study to analyse both absolute and relative differences in heart attack risk between the sexes across a range of risk factors in a general population, but they emphasise that it is an observational study, so no firm conclusions can be drawn about cause and effect.
“The presence of hypertension, smoking, and diabetes were associated with an increased risk of myocardial infarction in both women and men, but with an excess relative risk among women,” the authors say.
“Women should, at least, receive the same access to guideline-based treatments for diabetes and hypertension, and to resources to help lose weight and stop smoking as do men.”
In the UK, women with diabetes are 15% less likely than men with diabetes to receive all recommended care processes, and may be less likely to achieve target values when treated for cardiovascular risk factors.
While the overall impact of smoking, high blood pressure and diabetes on heart attack risk decreased in both sexes with age, the greater risk these factors had on the risk of heart attack in women relative to their impact in men persisted.
“Rising prevalence of lifestyle-associated risk factors, coupled with the ageing population, is likely to result in women having a more similar overall rate of myocardial infarction to men than is the case at present, with a subsequent significant additional burden on society and health resources,” the authors warn.
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.
Elizabeth RC Millett, Sanne AE Peters, Mark Woodward