Although obesity is linked to cardiovascular disease, it is unclear which measure of obesity is most predictive of disease or how different measures perform in various population groups. Small studies have indicated that the waist-to-hip ratio is more strongly related to the risk of myocardial infarction than the commonly used body mass index (BMI). Yusuf and colleagues used data from a large international study of myocardial infarction to study whether BMI or waist-to-hip ratio better predicted myocardial infarction.

The study of more than 27,000 participants in 52 countries investigated factors related to first myocardial infarction. All patients presented within 24 hours of symptom onset. Patients in cardiogenic shock and those with a history of chronic disease were excluded from the study. Each patient was matched with at least one age- and sex-matched control patient. Extensive data were gathered on demographic, socioeconomic, and lifestyle variables, as well as personal, family, and other risk factors for cardiovascular disease. Data from physical examination included standardized measurements of height, weight, waist and hip circumferences, and calculation of the BMI and waist-to-hip ratio.

Patients with myocardial infarction and control patients did not differ significantly in height. Marked differences in BMI and the prevalence of obesity were found between participant groups in Asia, Europe, Africa, South America, and North America. The waist-to-hip ratio also varied considerably by region, but the variations differed from those of the BMI. Overall, BMI was only slightly higher in patients with myocardial infarction compared with controls, and no differences were noted in the Middle East and Southern Asia participant groups. Conversely, the waist-to-hip ratio was greater in patients with myocardial infarction than in the control group in all regions of the world.

The risk of myocardial infarction increased with increasing BMI. Participants in the highest quintiles (BMI of more than 28.2 kg per m² in women or more than 28.6 kg per m² in men) had a higher (1.44-fold) increase in myocardial infarction compared with the lowest quintiles (BMI lower than 22.7 kg per m² in women or lower than 22.5 kg per m² in men). This relationship diminished substantially when adjusted for waist-to-hip ratio and disappeared completely after adjustment for other risk factors. Waist circumference alone was strongly related to risk of myocardial infarction, and this association remained significant after adjustment for other risk factors. Similarly, increasing hip circumference was significantly associated with lower risk for myocardial infarction after adjustment for BMI and height. The strongest relationship with myocardial infarction risk was with the waist-to-hip ratio. The relationship persisted after adjustment for other variables and was consistent in men and women. The odds of myocardial infarction increased with successive quintiles and had no threshold effect. Participants in the highest quintiles of waist-to-hip ratio had a 2.52-fold increase in risk compared with those in the lowest quintiles.

The authors conclude that waist-to-hip ratio has a graded and highly significant association with risk of myocardial infarction in all population groups studied. They recommend that waist-to-hip ratio replace BMI as an index of obesity in estimating risk of myocardial infarction.