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 researchers.

“The prevalence of class III obesity has increased dramatically in several countries and currently affects 6% of adults in the US, with uncertain impact on the risks of illness and death,” explained Cari M. Kitahara, PhD, of the National Cancer Institute in Bethesda, Md., and colleagues in PLOS Medicine.

To evaluate the risk of mortality and years of life expectancy lost related to class III obesity, investigators performed a pooled analysis involving class III obese (n=9,564) and normal-weight patients (n=304,011).

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For male and female patients, respectively, mortality rates expressed as deaths per 100,000 persons per year were higher among class III obesity participants than in normal-weight participants for heart disease (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% CI: 5.7- 7.3 years; BMI of 45 to 49.9 kg/m²: 8.9 years; 95% CI: 7.4-10.4 years; BMI of 50- 54.9 kg/m²: 9.8 years; 95% CI: 7.4-12.2 years; and BMI of 55 to 59.9 kg/m²: 13.7 years; 95% CI: 10.5-16.9 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 wrote the researchers.


  1. Kitahara C et al. Plos Medicine. 2014; doi: 10.1371/journal.pmed.1001673