(HealthDay News) — Class III obesity, defined as a body mass index (BMI) of 40 kg/m² or higher, is associated with a substantially higher total mortality compared with normal weight, according to research published online in PLOS Medicine.

Cari M. Kitahara, PhD, of the National Cancer Institute in Bethesda, MD, and colleagues performed a pooled analysis of 20 prospective studies to evaluate the risk of mortality and years of life expectancy lost related to class III obesity. Data from 9,564 class III obese participants and 304,011 normal-weight participants were analyzed.

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The researchers found that for men and women, respectively, mortality rates expressed as deaths per 100,000 persons per year were higher among class III obese participants than in normal-weight participants for heart disease (rate differences of 238.9 and 132.8), cancer (rate differences of 36.7 and 62.3), and diabetes (rate differences of 51.2 and 29.2).

Among class III obese participants, compared with normal-weight participants, increasing BMI was associated with increasing number of years of life lost (BMI of 40 to 44.9 kg/m²: 6.5 years; 95% confidence interval [CI], 5.7 to 7.3 years; BMI of 45 to 49.9 kg/m²: 8.9 years; 95% CI, 7.4 to 10.4 years; BMI of 50 to 54.9 kg/m²: 9.8 years; 95% CI, 7.4 to 12.2 years; and BMI of 55 to 59.9 kg/m²: 13.7 years; 95% CI, 10.5 to 16.9 years).

“Class III obesity is associated with substantially elevated rates of total mortality, with most of the excess deaths due to heart disease, cancer, and diabetes, and major reductions in life expectancy compared with normal weight,” the researchers wrote.


  1. Kitahara CM, Flint AJ, de Gonzalez AB, et al. Association between Class III Obesity (BMI of 40–59 kg/m2) and Mortality: A Pooled Analysis of 20 Prospective Studies. PLoS Med. 2014;doi:10.1371/journal.pmed.1001673.