March 11, 2011 (Cambridge, United Kingsdom) — A new study has cast doubt on the widely held belief that obesity in an apple shape, with fat accumulation around the stomach area, is more damaging in terms of cardiovascular risk than other types of obesity [1].

The study, published online in the Lancet on March 11, 2011, was conducted by the international group known as the Emerging Risk Factors Collaboration.

Coauthor Dr Emanuele Di Angelantonio (University of Cambridge, UK) commented to heartwire : "It has been thought that central adiposity (apple shape) is associated with a greater risk of cardiovascular disease than other types of obesity, but we have shown in our study that any one of three measures of obesity are equally associated with heart disease. So being an apple is no worse than being a pear. Both are bad."

Being an apple is no worse than being a pear. Both are bad.
Di Angelantonio claims the current study is more reliable than previous ones because it is prospective in design and therefore less liable to be affected by bias. "We followed 220 000 individuals for 10 years in a prospective fashion with measures of obesity recorded at baseline. The previous studies have mainly been of a case-control design, where they worked backward from the event. These are not nearly so accurate in estimating risk of particular factors."

He added: "We are not saying that visceral obesity is not important. All types of obesity are important, as they are all linked to cardiovascular disease. But what we are saying is that the apple shape is no riskier than other shapes, which is a big difference from previous opinion."

Obesity Does Not Add Much to Risk Prediction on Top of Other Measures

In the study, the researchers also examined the role obesity plays in risk scores for cardiovascular disease, and they found that if other risk factors are considered--such as diabetes, cholesterol, and blood pressure, as well as family history, age, and gender--body-mass index (BMI) or any other measure of obesity does not add much extra. "We are not saying that obesity is not important as a risk factor, because we know it contributes to many of the other risk factors already considered, such as diabetes and cholesterol. But we are saying that if you have information on history of diabetes, cholesterol, and blood pressure, then adding in a measure of obesity does not add to risk stratification," Di Angelantonio said.

In the paper, the authors explain that recommendations about the value of obesity for cardiovascular risk prediction vary in different guidelines. For example, the WHO and the US National Heart, Lung, and Blood Institute recommend assessment of both body-mass index (BMI) and waist circumference, while others such as Framingham do not include any adiposity measures. They say this divergence may reflect uncertainties in the data from previous studies. While one large case-control study (INTERHEART) suggested that waist-to-hip ratio was three times more strongly related to risk of MI than was BMI, but this has not been confirmed in prospective studies. They also point out that previous prospective studies of adiposity have often lacked concomitant measurement of lipids and other conventional risk factors, which has made it difficult to assess how obesity should be incorporated into risk-prediction scores.

They therefore conducted a prospective study to look at these issues. For this, they analyzed individual data from 221 934 participants from 17 countries in 58 prospective studies to produce reliable estimates of associations of BMI, waist circumference, and waist-to-hip ratio with first-onset cardiovascular-disease outcomes.

They found that in people with a BMI of 20 kg/m2 or higher, the risks of cardiovascular disease were similar based on measurements of BMI, waist circumference, or waist-to-hip ratio.

Hazard Ratio for CV Disease Based Related to Measurements of Obesity
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Measurement Hazard ratioa (95% CI) Hazard ratiob (95% CI)
BMI 1.23 (1.17–1.29) 1.07 (1.03–1.11)
Waist circumference 1.27 (1.20–1.33) 1.10 (1.05–1.14)
Waist-to-hip ratio 1.25 (1.19–1.31) 1.12 (1.08–1.15)
a. After adjustment for age, sex, and smoking status

b. After further adjustment for baseline systolic blood pressure, history of diabetes, and total and HDL cholesterol

Other results showed that the addition of information on BMI, waist circumference, or waist-to-hip ratio to a cardiovascular-disease risk-prediction model containing conventional risk factors did not notably improve risk discrimination or classification of participants to categories of predicted 10-year risk.

The authors conclude: "Whether assessed singly or in combination, body-mass index, waist circumference, and waist-to-hip ratio do not improve prediction of first-onset cardiovascular disease when additional information exists on blood pressure, history of diabetes, and cholesterol measures. . . . This finding applies to a wide range of circumstances and clinically relevant subgroups." But they add: "The main finding of this study does not, of course, diminish the importance of adiposity as a major modifiable determinant of cardiovascular disease."

Editorial: BMI Should Still Be Measured

In an accompanying Comment [2], Drs Rachel Huxley and David Jacobs (School of Public Health, University of Minnesota, Minneapolis) say that doctors should still measure BMI, as it is so strongly associated with chronic disease risk and serves as an "early warning." But they point out that the current results argue against the idea that waist circumference or waist-to-hip ratio should replace BMI as the measure of choice in clinical practice, at least for cardiovascular risk assessment. They add that this has its advantages, as BMI is easier to measure than the other indices.

Noting another of the study's findings--that the inclusion of BMI and waist circumference could only marginally compensate for the lack of information about total and HDL cholesterol in a risk-prediction model, the editorialists point out that this has dispelled the previous hope that assessment of body size could replace the cost, time, and inconvenience of blood lipids, which could be important, particularly in resource-poor settings.

http://www.medscape.com/viewarticle/738891