Waist To Hip Ratio -Best Predictor For Cardiac Problems

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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."

  1. 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.

The complete contents of Heartwire, a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.

Learning Objectives for This Educational Activity

Upon completion of this activity, participants will be able to:
  1. Describe the correlation between waist circumference and body mass index and measures of coronary atherosclerosis.
  2. Describe the correlation between waist-to-hip-circumference and measures of coronary atherosclerosis compared with waist circumference and body mass index.

Clinical Context

Obesity affects one third of US adults and predisposes to cardiovascular risk factors including insulin resistance, hypertension, and dyslipidemia, but it is unclear whether all the risks can be explained by an increased burden of atherosclerosis or if other mechanisms mediate the risk. In addition, BMI has been used as the primary standard for outcomes of obesity in studies, alternative measures including WC and WHR have demonstrated better correlations with cardiovascular risk than BMI.

This is a multiethnic, population-based study conducted in 1 US city on subjects who had 3 visits for 5 to 6 months to examine the correlation between 3 measures of obesity (BMI, WC, and WHR) and measures of atherosclerosis: CAC and MRI-detected aortic plaque.

Study Highlights

  • A population-based cohort of 6101 adults aged 18 to 65 years were visited at home for an interview, and 3398 participants aged 30 to 65 years returned for a second visit for blood and urine tests.
  • A third visit occurred for 2971 participants who received a detailed clinical examination, anthropometric measurements, abdominal MRI for aortic plaque, and 2 EBCT measurements of CAC.
  • EBCT scans were performed twice with 40 slices spanning the entire heart and CAC results averaged and expressed in Agatston units.
  • A threshold of 10 Agatston units was used for diagnosis of atherosclerosis.
  • Abdominal MRI was performed with 6 total slices of the infrarenal abdominal aorta, and increased signal intensity, luminal protrusion, and focal wall thickening were identified as atherosclerotic plaque.
  • BMI, WC, hip circumference, and WHR were calculated.
  • Hypertension was defined as systolic blood pressure of 140 mm Hg or higher, diastolic blood pressure of 90 mm Hg or higher, or use of antihypertensive medication.
  • Diabetes was defined by self-report, use of medications, or fasting glucose levels.
  • Hypercholesterolemia was defined by use of lipid-lowering medication or lipid levels for low-density lipoprotein, total cholesterol, or triglycerides.
  • Smoking was defined by smoking cigarettes within 30 days.
  • Only data were analyzed on participants who completed all 3 visits with complete imaging data for either EBCT or MRI.
  • Participants were divided into sex-specific quintiles based on BMI, WC, hip circumference, and WHR, and men and women within each quintile were combined.
  • Mean age was 45 years, 33% were white, 50% were black, and 18% were Hispanic.
  • Mean BMI was 31 kg/m2, 34% had hypertension, mean systolic blood pressure was 126 mm Hg, and mean diastolic blood pressure was 78 mm Hg.
  • 12% had diabetes, 25% were current smokers, 12% had dyslipidemia, and mean total cholesterol was 180 mg/dL.
  • 21% of participants (234 women, 349 men) had detectable CAC.
  • The prevalence of CAC increased across quintiles of WC and WHR, and the odds of prevalent CAC were greater for each quintile of WC and WHR vs each quintile of BMI in both men and women.
  • After adjustment for age, smoking, hypertension, diabetes, the prevalence of CAC was significantly increased in the highest quintile of WHR (odds ratio, 1.91; P < .001) but not any quintile of BMI or WC.
  • WHR consistently predicted CAC compared with either BMI or WC.
  • 39% of participants (499 women, 477 men) had detectable aortic plaque.
  • A 3-fold increase in the prevalence of aortic plaque was found for the fifth WHR compared with the first quintiles.
  • Neither BMI nor WC was significantly associated with aortic plaque.
  • WHR demonstrated significantly increased odds for aortic plaque in the fourth and fifth quintiles.
  • No positive association was found for BMI or WC for aortic plaque.
  • In women, WC less than 88 cm was associated with a greater prevalence of CAC with higher hip circumference, but this association was not found in men.
  • WHR demonstrated superior discrimination for prevalent CAC compared with BMI and WC in sex-specific analyses.

Pearls for Practice

  • Increased BMI and WC are weakly associated with increased burden of plaque, as measured by prevalent CAC or aortic plaque.
  • WHR discriminates aortic plaque and atherosclerosis more effectively than either BMI or WC.

Submitted by DMorgan on Wed, 08/29/2007 - 10:53pm.