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Overweight People Live Longer?

Thursday, January 3, 2013 // Uncategorized

Here’s a Physicians First Watch summary of a recent controversial JAMA article followed by the abstract from JAMA and a commentary on it from the Atlantic.  As the Gershwin song from Porgy and Bess says, “It ain’t necessarily so.”

Overweight Seems Associated with Lower All-Cause Mortality, Meta-Analysis Finds

 

Being overweight is associated with lower all-cause mortality than being normal weight, according to a JAMA meta-analysis, but editorialists are cautious in their interpretation.

 Researchers examined BMI and its relation to mortality in nearly 100 studies, altogether including 2.9 million people. People with higher levels of obesity (that is, with BMIs of 35 and above) had higher hazard ratios for all-cause mortality than those of normal weight (BMIs between 18.5 and 25).

However, BMIs between 25 and 30 were associated with a significantly lower risk (hazard ratio, 0.94) than normal weight, and BMIs of 30 to 35 did not show higher risks.

Editorialists say the reduced risk seen in overweight people could be an artifact, since the lower end of the normal BMI range has been found to confer a higher risk of mortality than the upper end of normal. They conclude: “Establishing BMI is only the first step toward a more comprehensive risk evaluation.”

Association of All-Cause Mortality With Overweight and Obesity Using Standard Body Mass Index Categories:  A Systematic Review and Meta-analysis FREE

Katherine M. Flegal, PhD; Brian K. Kit, MD; Heather Orpana, PhD; Barry I. Graubard, PhD
[+-] Author Affiliations

Author Affiliations: National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, Maryland (Drs Flegal and Kit); School of Psychology, University of Ottawa, Ottawa, Ontario, Canada (Dr Orpana); and Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland (Dr Graubard).

 

JAMA. 2013;309(1):71-82. doi:10.1001/jama.2012.113905.
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Importance  Estimates of the relative mortality risks associated with normal weight, overweight, and obesity may help to inform decision making in the clinical setting.

Objective  To perform a systematic review of reported hazard ratios (HRs) of all-cause mortality for overweight and obesity relative to normal weight in the general population.

Data Sources  PubMed and EMBASE electronic databases were searched through September 30, 2012, without language restrictions.

Study Selection  Articles that reported HRs for all-cause mortality using standard body mass index (BMI) categories from prospective studies of general populations of adults were selected by consensus among multiple reviewers. Studies were excluded that used nonstandard categories or that were limited to adolescents or to those with specific medical conditions or to those undergoing specific procedures. PubMed searches yielded 7034 articles, of which 141 (2.0%) were eligible. An EMBASE search yielded 2 additional articles. After eliminating overlap, 97 studies were retained for analysis, providing a combined sample size of more than 2.88 million individuals and more than 270 000 deaths.

Data Extraction  Data were extracted by 1 reviewer and then reviewed by 3 independent reviewers. We selected the most complex model available for the full sample and used a variety of sensitivity analyses to address issues of possible overadjustment (adjusted for factors in causal pathway) or underadjustment (not adjusted for at least age, sex, and smoking).

Results  Random-effects summary all-cause mortality HRs for overweight (BMI of 25-<30), obesity (BMI of ≥30), grade 1 obesity (BMI of 30-<35), and grades 2 and 3 obesity (BMI of ≥35) were calculated relative to normal weight (BMI of 18.5-<25). The summary HRs were 0.94 (95% CI, 0.91-0.96) for overweight, 1.18 (95% CI, 1.12-1.25) for obesity (all grades combined), 0.95 (95% CI, 0.88-1.01) for grade 1 obesity, and 1.29 (95% CI, 1.18-1.41) for grades 2 and 3 obesity. These findings persisted when limited to studies with measured weight and height that were considered to be adequately adjusted. The HRs tended to be higher when weight and height were self-reported rather than measured.

Conclusions and Relevance  Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality. The use of predefined standard BMI groupings can facilitate between-study comparison.

 

 

The Problem With The ‘Overweight People Live Longer’ Study

Lindsay AbramsThe Atlantic | Jan. 3, 2013, 9:43 AM | 1,832 | 3
 
 
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Yes, to some degree, having a higher BMI has been associated with a lower risk of death. But interpreting these new findings to mean anything more than that, and precisely that, is dangerous.

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The counterintuitive findings that people who are overweight live longer, published today in the Journal of the American Medical Association, couldn’t have been more perfectly timed, coming as it has right when people are resolving to be healthier — which involves, for many, losing weight.

 

In many places where this story has been picked up, including The New York TimesThe Wall Street Journal, and Time, the implication seems to be that the push to get people down to a “healthy” weight has been overblown.

But that being overweight is associated with increased lifespan isn’t new. It’s called the “obesity paradox,” and studies documenting it have lead to widespread speculation about the potential “protective benefits” of excess body fat.

For some health advocates, the implication is downright offensive. Walter Willett of the Harvard School of Public Health, for example, lost his cool this morning on NPR, declaring, “This study is really a pile of rubbish and no one should waste their time reading it.”

But the study’s author, Katherine Flegal of the Centers for Disease Control and Prevention, mounted a solid defense: “It’s statistically significant.” Those three words carry weight — if an association has been found to be significant, it tells us that if nothing else, we need to acknowledge that the results are in some way legitimate and warrant our attention.

The findings are without doubt interesting, which on its own makes the study worth reading. The problem is that despite the grandness of the meta-analysis — it takes into account over 3 million people! — it still has an extremely limited scope. It looks at BMI, and only BMI, in relation to death, regardless of cause. It’s impossible to report on its baseline conclusion without taking into account substantial caveats. 

This can be said of any study where one thing is found to be associated with another, but in this case the findings are particularly amenable to being mistakenly interpreted as instructions, along the line of: “You should gain weight to live longer.” In this case, its real value is that it highlights the problems we always run into when attempting to talk about weight and healthy living.

Aside from the obvious limitations — people who pass away after a lengthy period of disease, for example, will likely be thinner than they might have been had they died unexpectedly — the study fails to take into account any of the various other measures used to assess health. It ignores blood pressure, blood sugar, and cholesterol — high levels of all are directly associated with a variety of chronic conditions and diseases — not to mention mental health and life satisfaction scores. As another large-scale study recently pointed out, longevity isn’t everything. The population as a whole is living longer than it was twenty years ago, but the number of those years spent in poor health are increasing as well. 

That BMI is an imperfect measure of body size is emphasized here as well. The simple calculation of height and weight ignores gender, age, and muscle mass — I remember being hopelessly confused the first time a guy told me his goal was to gain weight. Where on the body fat is located is important as well (belly fat, for example, poses a greater health risk than excess weight that’s more evenly distributed). A BMI in the “overweight” range, from 25 to just below 30, encompasses a broad sweep of body diversity: A frequently cited argument is that Michael Jordan, at his prime, would have been classified as overweight. By almost any other measure but BMI, we would almost certainly put him in the range of ideal health. 

Just as BMI glosses over such variance, so, too, have news outlets reporting on the study.

While in the most basic of ways, it makes sense to pay attention to the number on the scale, it only gives us one metric of health that, if not understood in context, is basically useless. If we could get used to looking at weight more holistically, in terms of overall health, the link between BMI and longevity wouldn’t be so shocking.

From TheAtlantic – shaping the national debate on the most critical issues of our times, from politics, business, and the economy, to technology, arts, and culture.

SOME OF THE CONTROVERSY INVOLVES THE FACT THAT THIS IS A META-ANALYSIS OR CRUNCHING OF DATA FROM MULTIPLE STUDIES.  THESE TYPES OF STUDIES ARE ONLY AS GOOD AS THEIR INDIVIDUAL COMPONENTS.  SOME OF THE STUDIES ALLOWED SELF REPORTING OF HEIGHT AND WEIGHT.  BOTTOM LINE: BMI DOESN’T TELL THE WHOLE STORY.

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