In
an analysis of nearly 100 studies that included approximately 3 million adults,
relative to normal weight, overall obesity (combining all grades) and higher
levels of obesity were both associated with a significantly higher all-cause
risk of death, while overweight was associated with significantly lower
all-cause mortality, according to a study in the January 2 issue of JAMA.
"Estimates of the relative mortality risks associated with normal weight, overweight, and obesity may help to inform decision making in the clinical setting," according to background information in the article.
Katherine
M. Flegal, Ph.D., of the National Center for Health Statistics, Centers for
Disease Control and Prevention, Hyattsville, Md., and colleagues conducted a
study to compile and summarize published analyses of body mass index (BMI) and
all-cause mortality that provide hazard ratios (HRs) 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. Regions of origin of participants included the United States or Canada (n = 41 studies), Europe (n = 37), Australia (n = 7), China or Taiwan (n = 4), Japan (n = 2), Brazil (n = 2), Israel (n = 2), India (n = l), and Mexico (n = l).
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. Regions of origin of participants included the United States or Canada (n = 41 studies), Europe (n = 37), Australia (n = 7), China or Taiwan (n = 4), Japan (n = 2), Brazil (n = 2), Israel (n = 2), India (n = l), and Mexico (n = l).
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
researchers found that the summary HRs indicated a 6 percent lower risk of
death for overweight; a 18 percent higher risk of death for obesity (all
grades); a 5 percent lower risk of death for grade 1 obesity; and a 29 percent
increased risk of death for grades 2 and 3 obesity.
The
authors note that the finding that grade 1 obesity was not associated with
higher mortality suggests that that the excess mortality in obesity may
predominantly be due to elevated mortality at higher BMI levels.
The
researchers add that 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."
The
use of predefined standard BMI groupings can facilitate between-study
comparisons, the authors conclude.
Editorial: Does Body Mass Index Adequately Convey a Patient's
Mortality Risk?
"Can
overweight as defined by BMI actually have a protective association with
mortality?" write Steven B. Heymsfield, M.D., and William T. Cefalu, M.D.,
of the Pennington Biomedical Research Center, Baton Rouge, La., in an
accompanying editorial.
"The
presence of a wasting disease, heart disease, diabetes, renal dialysis, or
older age are all associated with an inverse relationship between BMI and
mortality rate, an observation termed the obesity paradox or reverse
epidemiology. 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 in light of the studies by Flegal
et al and others."
"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."
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Journal Reference:
1. Katherine M. Flegal, Brian K. Kit, Heather
Orpana, Barry I. Graubard. Association of All-Cause Mortality With
Overweight and Obesity Using Standard Body Mass Index CategoriesA Systematic
Review and Meta-analysis. JAMA, Jan 2013 DOI: 10.1001/jama.2012.113905
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JAMA and Archives Journals (2013, January 1). Best to be
overweight, but not obese? Higher levels of obesity associated with increased
risk of death. ScienceDaily. Retrieved January 2, 2013, from
http://www.sciencedaily.com/releases/2013/01/130101182008.htm