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Study: Overweight people have lower risk of death

Wednesday January 2, 2013
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Relative to normal weight, overall obesity and higher levels of obesity were associated with a significantly higher all-cause risk of death, but being overweight was associated with significantly lower all-cause mortality, according to an analysis of nearly 100 studies that included about 3 million adults.

"Estimates of the relative mortality risks associated with normal weight, overweight and obesity may help to inform decision-making in the clinical setting," researchers wrote in background information for the study, which appears in the Jan. 2 issue of the Journal of the American Medical Association.

Katherine M. Flegal, PhD, of the National Center for Health Statistics at the Centers for Disease Control and Prevention, and colleagues conducted a study to compile and summarize published analyses of body mass index and all-cause mortality that provide hazard ratios for standard BMI categories. For the review and meta-analysis, the researchers identified 97 studies that met inclusion criteria, which provided a combined sample size of more than 2.88 million individuals and more than 270,000 deaths.

Of the studies, 41 took place in the United States or Canada, 37 took place in Europe and the rest took place in Australia, China or Taiwan, Japan, Brazil, Israel, India and Mexico.

The researchers found that the summary hazard ratios indicated a 6% lower risk of death for being overweight, an 18% higher risk of death for obesity (all grades), a 5% lower risk of death for grade 1 obesity and a 29% increased risk of death for grades 2 and 3 obesity.

The authors noted that the finding that grade 1 obesity was not associated with higher mortality suggests that the excess mortality in obesity may be predominantly due to elevated mortality at higher BMI levels.

They added their findings are consistent with observations of lower mortality among overweight and moderately obese patients: "Possible explanations have included earlier presentation of heavier patients, greater likelihood of receiving optimal medical treatment, cardioprotective metabolic effects of increased body fat and benefits of higher metabolic reserves."

In an accompanying editorial, Steven B. Heymsfield, MD, and William T. Cefalu, MD, of the Pennington Biomedical Research Centre in Baton Rouge, La., wrote: "The optimal BMI linked with lowest mortality in patients with chronic disease may be within the overweight and obesity range. Even in the absence of chronic disease, small excess amounts of adipose tissue may provide needed energy reserves during acute catabolic illnesses, have beneficial mechanical effects with some types of traumatic injuries and convey other salutary effects that need to be investigated.

"Not all patients classified as being overweight or having grade 1 obesity, particularly those with chronic diseases, can be assumed to require weight-loss treatment. Establishing BMI is only the first step toward a more comprehensive risk evaluation."

The study is available at http://jama.jamanetwork.com/article.aspx?articleid=1555137.

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