Waist Measure and BMI Best Predict Heart Disease Death Risk

January 29, 2013

ROCHESTER, Minnesota — Combining a measure of central obesity with body-mass index (BMI) is better for assessing mortality risk in patients with coronary artery disease (CAD) than using BMI alone, new research shows [1]. Dr Thais Coutinho (Mayo Clinic, Rochester, MN) and colleagues found that those with normal BMI but central obesity--increased fat deposits around the waist, especially in relation to the hips--were at highest risk of dying compared with subjects with other adiposity patterns. They report their findings in a study published in the February 5, 2013 issue of the Journal of the American College of Cardiology.

"If all we do is the BMI measurement, we may be missing a subset of patients who have a low BMI but are centrally obese, and we'd be neglecting the opportunity to identify and counsel and treat these patients who would be at increased risk of dying," Coutinho told heartwire . The group with normal BMI but central obesity had, for example, a 61% increased risk of dying compared with those with a BMI of 30 and no central obesity in the study, she noted.

All it really takes is a scale and a tape measure, so anybody can do it anywhere in the world.

She does not advocate eliminating BMI as a clinical measure, however, but said that people need to understand its limitations. "BMI has a poor correlation with body fatness. It's still a risk factor for having a heart attack, but when it comes to predicting chance of dying, it's not so well correlated. That's why it's important to document both BMI and central obesity, to better risk stratify our patients. This is very clinically applicable: it's a simple test that's not expensive or invasive--all it really takes is a scale and a tape measure, so anybody can do it anywhere in the world."

First to Examine CAD Mortality Using Both BMI and Central Obesity

Coutinho explained that the "obesity paradox"--whereby those with a high BMI tend to die less from coronary disease--"is a well-known phenomenon that has always been a puzzle. We have previously shown that if central obesity is used to define obesity instead of BMI, this paradox doesn't exist."

"In this paper, we went a step further," she noted. "We were hypothesizing that if we were able to combine BMI with measures of central obesity, we would then be able to better stratify the risk of the patient, the risk for mortality. And that's precisely what we found."

She and her colleagues performed a systematic review of the literature, creating a database comprising 15 547 participants with CAD taking part in five studies--from three continents--that assessed risk for mortality associated with either waist circumference or waist-to-hip ratio. They excluded patients with very low BMIs (<18.5 kg/m2). The mean age of participants was 66 years, and 55% were men.

This is the first study to primarily focus on assessment of mortality in patients with CAD based on a combined assessment of BMI and central obesity, the researchers say, although secondary analyses from three prior studies have evaluated prognosis associated with body adiposity patterns, they note.

We need to pay more attention to fat distribution than total fat itself; that is the message.

There were 4699 deaths over a median follow-up of 4.7 years. Subjects with normal weight but central obesity had the worst long-term survival: a person with BMI of 22 kg/m2 and waist-to-hip ratio (WHR) of 0.98 had higher mortality than a person with similar BMI but WHR of 0.89 (hazard ratio [HR], 1.10); a person with BMI of 26 kg/m2 and WHR of 0.89 (HR, 1.20); a person with BMI of 30 kg/m2 and WHR of 0.89 (HR, 1.61); and a person with BMI of 30 kg/m2 and WHR of 0.98 (HR, 1.27) (P < .0001 for all comparisons).

"Subjects with normal-weight central obesity have the worst long-term survival compared with subjects with other adiposity patterns," the researchers stress. "Furthermore, being overweight or obese by a BMI criterion does not lead to higher mortality in the absence of central obesity."

"There is something about the types of fat we have," Coutinho explained. "The fat in the abdomen is worse than the fat in the hips; the latter appears to be protective. We need to pay more attention to fat distribution than total fat itself; that is the message. Fat deposits inside the abdomen and between the organs are very metabolically active, they are associated with hypertension, inflammation, insulin resistance, etc: central obesity is bad."

Doctors Must Watch Out for Normal BMI, Centrally Obese Patients

Coutinho said that it is vital that physicians and patients understand these findings. "There are a lot of studies showing the obesity paradox, and of course we are in the time now of New Year's resolutions: everybody decides they are going to lose weight, and I don't want people to think that because BMI is inversely related to mortality, the obesity paradox, that they should throw their New Year's resolutions out the window."

It is therefore incumbent on doctors to extend their inquiries beyond BMI, she said. Otherwise, those with normal-weight central obesity may go unnoticed during clinical assessments when, in reality, they may require the greatest attention in terms of counseling to exercise, for example. Physician diagnosis of obesity "almost triples the odds of achieving successful weight loss among subjects with CAD," she and her colleagues note.

"Our findings support the concept that clinicians should go beyond BMI when assessing mortality risk in patients with CAD, because combining BMI with measures of central obesity allows us to better discriminate those at the highest and lowest risk of dying."

Coutinho has disclosed no relevant financial relationships; disclosures for the coauthors are listed in the paper.