Role of Excess Weight in Risk of Death

In an analysis of 97 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. Katherine M. Flegal, from the US Centers for Disease Control & Prevention (CDC; Maryland, USA), and colleagues completed 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. 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% lower risk of death for overweight; a 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.  Observing that: “Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality,” the study authors conclude that: “Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality.”