Smoking, high lipid concentrations, and stress are the main risk factors for coronary artery disease (the major cause of heart attack) across all world regions. A secondary analysis by the same authors highlights how stress is responsible for around a fifth of heart attacks worldwide.

Cardiovascular disease is estimated to be the largest cause of death and disability worldwide; 80% of death and disability occurs in low-income and middle-income countries, although the knowledge base of the importance of risk factors is largely derived from developed countries. This means that the effect of such factors on the risk of coronary heart disease in most regions of the world is unknown.

Salim Yusuf (McMaster University, Canada) and colleagues did a case-control study of acute myocardial infarction (heart attack) patients in 52 countries, representing every inhabited continent. Around 15,000 cases and 15,000 controls matched for age, sex, and location were enrolled. The relation of smoking, history of hypertension or diabetes, waist to hip ratio, dietary patterns, physical activity, consumption of alcohol, blood lipids, and psychosocial factors to heart attack were analysed and their risk values for heart attack calculated.

The two main risk factors identified from the study were smoking (risk value of 2.9, ie, a nearly threefold increased risk of heart attack for smokers compared with never smokers) and raised lipid concentrations (risk value 3.25).

Other important risk factors for heart attack were psychosocial factors such as stress (2.7), diabetes (2.4), family history of high blood pressure (1.9), and abdominal obesity (1.1). Three risk factors were protective against heart attack: the daily consumption of fruit and vegetables (0.7), regular physical exercise (0.86), and moderate alcohol consumption (defined as moderate alcohol intake three times a week; [0.91]). These associations were found in men and women, old and young, and in all regions of the world.

Professor Yusuf comments: “Our study has shown that nine easily measured risk factors are associated with more than 90% of the risk of an acute myocardial infarction in this large global case-control study.

These results are consistent across all geographic regions and ethnic groups of the world, men and women, and young and old. Although priorities can differ between geographic regions because of variations in prevalence of risk factors and disease and economic circumstances, our results suggest that approaches to prevention of coronary artery disease can be based on similar principles throughout the world. Therefore, modification of currently known risk factors has the potential to prevent most premature cases of myocardial infarction worldwide.”

The same investigators did a more detailed analysis of the psychosocial factors associated with increased heart-attack risk. Around 11,000 of the 15,000 cases from the main study and 13,600 controls were assessed. Psychosocial stress was assessed by four simple questions about stress at work and at home, financial stress, and major life events in the past year. Cases reported higher prevalence of all four stress factors: of those cases still working, 23% experienced several periods of work stress compared with 18% of controls; 10% experienced permanent work stress during the previous year compared with 5% of controls. Around 12% of cases had several periods of stress at home compared with around 9% of controls; financial problems were a major contributor to stress at home.

Overall, the relationship between stress and increased risk of heart attack was consistent across all world regions and ethnic groups studied, contributing to over a fifth (22%) of all heart attacks worldwide.

In an accompanying commentary, Majid Ezzati (Harvard School of Public Health, USA) states that INTERHEART provides further confirmation that for many common cardiovascular risk factors, differences in total risk across populations are more a result of variations in exposure and background levels of disease than an outcome of different causal processes. For these risks, Ezzati says: “In parallel to advancing our basic understanding of causative mechanisms, we can safely begin to pay attention to design of effective interventions, and more importantly to programmes for delivery of available interventions to those at need.”