(HealthDay News) – Obesity (all grades combined) and grades 2 and 3 obesity, based on standard body mass index (BMI) categories, correlate with increased risk of all-cause mortality, while overweight is associated with decreased risk compared with normal weight, according to a review published in the Jan. 2 issue of the Journal of the American Medical Association.

Katherine M. Flegal, PhD, from the U.S. Centers for Disease Control and Prevention in Hyattsville, MD, and colleagues conducted a systematic review of reported hazard ratios of all-cause mortality using standard BMI categories to examine the relative risks associated with normal weight, overweight, and obesity. Ninety-seven studies were included, with a combined sample size of more than 2.88 million individuals and more than 270,000 deaths.

The researchers found that, relative to normal weight, the random-effects summary all-cause mortality hazard ratios were 0.94 (95% confidence interval [CI], 0.91–0.96) for overweight; 1.18 (95% CI, 1.12–1.25) for all grades of obesity 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. The findings persisted when the analysis was limited to studies that were adequately adjusted for measured weight and height. Using self-reported rather than measured weight and height tended to result in higher hazard ratios.

“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,” write the authors of an accompanying editorial. “Establishing BMI is only the first step toward a more comprehensive risk evaluation.”

Both authors of the editorial disclosed financial ties to the pharmaceutical industry.

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