Class III obesity linked with substantially elevated rates of total mortality: Study

Otherwise healthy, non-smoking adults with BMI values within the class III obesity range may considerably extend their life expectancy by avoiding additional weight gain, according to a study published in PLOS Medicine.

Cari Kitahara, PhD, MHS, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Md., and colleagues pooled (combined) data from 20 large study populations in the United States, Sweden, and Australia to evaluate the risk of death during the study period, overall and from a wide range of causes, in adults with BMI values of 40 and above compared with adults with BMI values in the normal-weight, or “healthy” BMI range (18.5-24.9). Study participants were all never smokers and without a history of heart disease, cancer, stroke, or emphysema at baseline. The study population consisted of 9,564 adults in the class III obesity group and 304,011 adults in the normal-weight group.

“We found that total mortality rates were substantially [about 2.5 times] higher in adults with BMI values in the class III obesity range [40+] than those with those in the normal-weight range [18.5-24.9],” Kitahara said. “Specifically, the class III obesity group had an extra 509 deaths annually per 100,000 men and an extra 382 deaths annually per 100,000 women. Most of this excess was due to deaths from heart disease, followed by deaths from cancer and diabetes, chronic liver disease, and kidney diseases.”

The reseachers also found that life expectancy was much lower in the class III obesity group compared with normal-weight, ranging between 6.5 fewer years of life for BMI 40 to 44 to 13.7 fewer years for BMI 55 to 59. 

“This loss in life expectancy is similar to what we and others have observed when comparing current versus never cigarette smokers,” Kitahara said.

This study is the first study to describe with precision the risk of total and cause-specific deaths for adults who are extremely obese (class III). Class III (or extreme) obesity was once a relatively uncommon condition, but the prevalence has been increasing dramatically over the last three decades. Currently, approximately 6% of US adults are classified as extremely obese, which, for a person of average height, is more than 100 lbs over the recommended range for normal weight. 

“Prior to our study, little was known about the impact of extreme obesity on overall health and risk of dying from a broad range of causes,” Kitahara said. “As extreme obesity continues to increase in prevalence in the United States, we will begin too see increases in mortality, and morbidity, associated with this condition. The purpose of our study was to describe the relationship between class III obesity and mortality risk, not to make recommendations to leaders in healthcare. We hope these data will be informative to policy-makers and managers.”