People with body mass index (BMI) above 40 lose at least 6 1/2 years, on average, of expected life span, a study now shows. The number of years lost increases with the degree of obesity, reaching nearly 14 years for the most obese—those with a BMI above 55.
The study found that the reduction in life expectancy associated with being extremely obese was similar to that of adults who smoke. As a person’s obesity increases to higher levels, life expectancy can become shorter than that of smokers.
The findings come from pooled analysis of 20 prospective studies from the United States, Sweden, and Australia. Cari M. Kitahara et al. described what is believed to be the largest study to date of the health consequences of severe obesity in the July 8 in PLoS Medicine.
Kitahara et al. estimated sex- and age-adjusted total and cause-specific mortality rates (deaths per 100,000 persons/year) and multivariable-adjusted hazard ratios for adults, 19–83 years old, classified as obese class III (BMI, 40.0–59.9 kg/m2) compared with those classified as normal weight (BMI 18.5–24.9, kg/m2).
They associated class III obesity with substantially increases in overall mortality, mostly due to heart disease, cancer, and diabetes.
Reuters reported that people with a BMI of 40 to 44.9 lost an average of 6.5 years of life. They add that researchers could not say whether the results would hold for poorer, non-Western populations.
The study found that extreme obesity could be even more dangerous for men than for women, and for younger adults than older ones. Among men with class III obesity, the rate of death attributable to heart disease and diabetes increased greatly, compared with rates of normal-weight men. For women in the same obesity category, cancer deaths were much greater than among normal-weight women.
“While once a relatively uncommon condition, the prevalence of class III, or extreme, obesity is on the rise,” Kitahara said in a statement reported by TIME. “Prior to our study, little had been known about the risk of premature death associated with extreme obesity.”
According to the Los Angeles Times, the number of people with a BMI over 40 (for example, a 5-foot-6 person weighing 250 pounds or more) has increased 4-fold since the 1980s. The population with a BMI over 50 (for example, a 5-foot-10 person weighing more than 350 pounds) has grown by 10% in the same period.
The medical costs for these patients are significant, accounting for 1 in 5 healthcare dollars spent per capita in the year 2000.
“If current global trends in obesity continue, we must expect to see substantially increased rates of mortality due to these major causes of death, as well as increasing healthcare costs,” the authors conclude.
The new calculation is unlikely to cause people with extreme obesity to shed pounds—”that pre-supposes that the main reason people don’t lose weight is lack of willpower, and I’d argue that’s not the case,” Lee Kaplan, director of the weight center at Massachusetts General Hospital, told Reuters. “But it could have a beneficial effect if it galvanizes society to change in ways that stop promoting obesity and to develop aggressive treatments for extreme obesity.”
In the United States, 36% of adults are obese, according to the National Center for Health Statistics (see figure above). The incidence of BMIs of 40 or higher has more than quadrupled since the mid-1980s, and about 18% of U.S. adults are extremely obese.