Waist-to-Hip Ratio a Better Marker of Subclinical Atherosclerosis Than BMI and Waist Circumference

August 15, 2007 — The relationship of the waist to hip measurement is independently associated with prevalent atherosclerosis, as measured by coronary artery calcium (CAC) imaging, and is a better discriminator of subclinical disease than other common measures of obesity, such as body mass index (BMI) or waist circumference alone, a new study has shown.[1] Those with the largest waist-to-hip ratio (WHR) were almost twice as likely to have calcium deposits in the coronary arteries compared with those with the least calcification, report investigators.
"These data confirm what others have shown for clinical events, that is when you link this data to some of the large outcome studies, it really does establish a consistent message that these measures of body shape — waist and the waist-to-hip ratio — predict not just clinical events but also atherosclerotic burden," senior investigator Dr James de Lemos (University of Texas Southwestern Medical Center, Dallas, TX) told heartwire. "It also suggests that part of the mechanism in which central adiposity contributes to increased risk is through this increased atherosclerotic burden."
The results of the study are published in the August 14, 2007 issue of the Journal of the American College of Cardiology.
Data from the Dallas Heart Study
Speaking with heartwire, de Lemos said the large INTERHEART study, previously reported by heartwire, showed that the WHR and waist circumference were excellent predictors of cardiovascular events. With this in mind, the group sought to determine the underlying mechanism responsible for this increased cardiovascular risk. Some part of this risk is likely driven by atherosclerosis in the coronaries and the aorta, although high blood pressure, left ventricular hypertrophy, or inflammation and thrombosis have all been proposed as risk factors explaining the increased morbidity and mortality risk associated with obesity, explained de Lemos.
Additionally, de Lemos noted there is a complex relationship between BMI and cardiovascular risk, an almost J-shaped relationship, where those with a very-low BMI having greater atherosclerotic burden than those with a higher BMI. Also, BMI doesn't reflect obesity, but rather mass, and is not a measure of central adiposity and cardiovascular risk. The purpose of this study, he said, was to evaluate the association between different measures of obesity and atherosclerosis in addition to determining if obesity was associated with subclinical cardiovascular disease.
Investigators obtained data from the Dallas Heart Study, a large, multiethnic urban population of patients who successfully completed electron-beam computed tomography (EBCT) to detect coronary artery calcium and magnetic resonance imaging (MRI) to detect aortic plaque. They found that the likelihood of coronary calcification grew in direct proportion to increases in the WHR. In multivariate analysis, after adjusting for standard risk factors, prevalent coronary artery calcium was more frequent in the fifth versus first quintile of WHR. Those with the largest WHR were nearly twice as likely to have calcium deposits in their coronary arteries as those with the smallest WHR. There was no independent positive association observed for BMI or waist circumference.
"The finding that was most striking to me was the linear association with the waist-to-hip ratio," said de Lemos. "We don't have huge statistical power here so this will need to be confirmed in other studies, but it is interesting that this is a linear, step-wise association across the quintiles. From a public health perspective, this is not the sort of thing where we only look at the guy with the biggest beer belly and say this guy is the one to worry about. This thing may have broader implications in the sense that the average person, even though they are average by US standards, still appears to have more atherosclerosis than people with the lowest waist-to-hip ratio."
Among those who underwent MRI, the investigators also showed that the risk of atherosclerotic plaque in the aorta was three times as high in those with the largest WHR compared with those who had the smallest WHR.
The associations between obesity measurements and atherosclerosis in this study, said de Lemos, mirror those observed between obesity and cardiovascular mortality and suggest that obesity contributes to the risk via increased atherosclerotic burden. As to why WHR is a better measure of subclinical disease, de Lemos said it is an indexed value to lower body girth and provides a more precise assessment of relative central adiposity across the body sizes compared with waist circumference. Additionally, there is some evidence that fat accumulated in the hips might be cardioprotective.
"That appears to be the case in this study," said de Lemos. "Large hips seemed to be protective if you had a normal or smaller waist. On the other hand, it didn't appear protective if the waist was greater than the median value. Having big hips doesn't protect you if you let your belly get too big."
See R, Abdullah SM, McGuire DK et al. The association of differing measures of overweight and obesity with prevalent atherosclerosis. J Am Coll Cardiol 2007;50:752-759.