Obesity and Cardiovascular Risk: Does Size Matter?

A very large new study finds that obesity — no matter how it is calculated — is not an important independent predictor of cardiovascular disease. A report from the Emerging Risk Factors Collaboration published online in the Lancet analyzed individual records from more than 220,000 people without known cardiovascular disease and found that none of the traditional methods to categorize obesity — BMI, waist circumference, and waist-to-hip ratio — provided significant additional information about CV risk beyond that already provided by systolic blood pressure, diabetes, and lipids.

The authors wrote that their finding “does not, of course, diminish the importance of adiposity as a major modifiable determinant of cardiovascular disease” but that “because excess adiposity is a major determinant of the intermediate risk factors… our findings underscore the importance of controlling adiposity to help prevent cardiovascular disease.” The authors also say that their results “reliably refute previous recommendations to adopt baseline waist-to-hip ratio instead of BMI as the principal clinical measure of adiposity.”

In an accompanying comment, Rachel Huxley and David Jacobs Jr. write that “BMI continues to be useful as an indicator of adiposity” and should be “used with good clinical judgment.” However, they note, “size still matters… but not in the way we once thought.”

Yoni Freedhoff, author of the highly regarded Weight Matters blog, provided the following comment to CardioBrief:

I think what’s important to remember in reading this article is the fact that the person sitting in front of us in our offices is in fact a person and not a number.  It would also seem from here that to chastise them solely on the basis of their weight, BMI,  waist-circumference or waist-to-hip ratio, while always unhelpful, as far as cardiovascular outcomes go, may in fact be quite unfair.  Ultimately clinicians need to treat overweight and obese patients the same way they would their healthy weight folks and that regardless of weight, it’s exceedingly important for clinicians to investigate and manage the usual suspects – blood pressure, lipid levels, fasting glucose and HbA1c.  No doubt that obesity, especially extreme obesity, carries with it risk, has many co-morbidities, negatively impacts on quality of life and can shorten lifespan as a whole, but that certainly doesn’t mean that the obese patient’s medical care on a whole should suffer.

Here is the Lancet press release:

“APPLE SHAPED” OBESITY IS AS BAD FOR HEART AS OTHER OBESITY (The Lancet)

An international study of 220,000 people has challenged the idea that obese people who have an “apple shape” (fat deposits on the middle section of the body) are at higher risk of heart attacks and strokes than obese people with other types of fat distribution. These are the conclusions of an Article published Online First and in an upcoming Lancet, from the Emerging Risk Factors Collaboration, a consortium of 200 scientists from 17 countries led from the University of Cambridge, UK.

Some earlier studies had claimed that people with “central obesity” (as assessed by the ratio of the waist to hip circumference, or “waist-to-hip” ratio) have 3 times greater risk of heart attack than people with general obesity (as assessed by the body-mass index (BMI), or the weight divided by the height squared). However, these earlier studies had major design limitations.

The current study involved over 220,000 adults, each monitored for almost a decade, of whom over 14,000 developed a heart attack or stroke during monitoring. The researchers confirmed that obesity is a major determinant of cardiovascular disease, but that body mass index (BMI), waist circumference, and waist-to-hip ratio each had a similar impact on the risk of subsequent heart attack and strokes.

A further finding of this study is that BMI, waist circumference, and waist-to-hip ratio, whether assessed singly or in combination, do not improve cardiovascular disease risk prediction in people in developed countries when additional information is available for systolic blood pressure, history of diabetes, and lipids.

This result highlights the value of GPs continuing to measure blood cholesterol and blood pressure levels. The findings should also help guide medical practice worldwide because national and international guidelines have provided differing recommendations about the value of clinical measures of obesity for prediction of cardiovascular disease risk in primary prevention.

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.”

In a linked Comment, Dr Rachel R Huxley and Dr David R Jacobs Jr, School of Public Health, University of Minnesota, conclude: “BMI used with good clinical judgment is highly appropriate in adults because it is so strongly associated with chronic disease risk, although we caution that it is correlated with height in children. Many overweight or obese adolescent, young adult, and middle-aged individuals with few risk factors for cardiovascular disease will develop that risk relatively soon, so BMI should serve as an early warning, both to them and their general practitioners. But discriminating which overweight individuals without current risk factors for cardiovascular disease will go on to develop those risk factors, and ultimately clinical cardiovascular disease, remains a challenge—here, blood tests continue to be helpful.”

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Comments

  1. Larry,

    Your postings are almost always stellar, but I gotta say the headline of this piece doesn’t work for me.

    I haven’t combed the details of the report, but the release says:
    “The main finding of this study does not, of course, diminish the importance of adiposity as a major modifiable determinant of cardiovascular disease.”

    In other words, while the study finds that obesity may not be an important independent predictor of cardiovascular disease, since it is a modifiable determinant, the authors are saying it still does matter.

  2. Hi Andrew,

    Thanks for the “stellar” comment! Your point is well taken, but in my defense I would say this:

    1. The title is taken from the title of the editorial, which is (as I quoted): “size still matters… but not in the way we once thought.”

    2. I used a question mark.

    3. Both the study and the editorial agree that in assessing risk obesity does NOT add independent value beyond traditional risk factors. So in that perhaps more limited sense the title is appropriate.

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