Being overweight was associated with significantly lower all-cause mortality relative to normal weight, while grade 1 obesity was not associated and grades two and three obesity were associated with significantly higher all-cause mortality, a meta-analysis found.
The meta-analysis included 97 studies made up of nearly 2.9 million people and more than 270,000 deaths. Results appeared Jan. 2 at the Journal of the American Medical Association.
Hazard ratios were calculated for normal weight (BMI of 18.5-25) compared to overweight (BMI of 25-30), obesity (BMI of 30 or more), grade 1 obesity (BMI of 30-35), and grades 2 and 3 obesity (BMI of 35 or more). HRs were 0.94 (95% CI, 0.91-0.96) for being 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 authors noted that elevated mortality at higher BMI levels may account for the excess of mortality in this population.
Researchers noted, "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."