Figures from the Centers for Disease Control and Prevention show that nearly 35 percent of adults in the U.S. are obese. For these individuals, their condition comes with health consequences such as increased risks for heart disease, type 2 diabetes, stroke and certain types of cancer and while many may already be aware of these obesity-related health problems, a new study may be able to highlight the dangers of obesity by focusing on the life expectancy and mortality risks of obese individuals.

For the new study published in the journal PLOS Medicine on July 8, Cari Kitahara, from the Division of Cancer Epidemiology and Genetics at the National Cancer Institute in Bethesda, Maryland, and colleagues analyzed data from 20 large studies from Australia, Sweden and the U.S. involving more than 9,500 adults with extreme obesity who never smoked and over 304,000 individuals with normal weight to assess the mortality risks associated with class 3 obesity, a condition marked by a body mass index (BMI) of 40 to 59 kg/m2.

Technically, people who are overweight have a BMI of 25.0 to 29.9. Individuals who are obese have a BMI of 30 or higher and those with class III obesity, or extreme obesity, have BMI of at least 40. Individuals suffering from extreme obesity have the highest risks for weight related diseases and early death.

The researchers found that compared with people with normal weight, obese individuals are likely to die 6.5 to 13.7 years earlier. Individuals with BMI of 44 to 44.9 reduce their life expectancy by 6.5 years on average while those whose BMI were between 45 and 49.9 are at risk of dying 8.9 years earlier.

The subjects in the study with normal weight and smoked cigarettes lost 8.9 years but their life span was comparable or even longer than those of obese individuals. Individuals with BMI of 50 to 54.9, for instance, are likely to die earlier than smokers as they reduce their life expectancy by 9.8 years while those with BMI of 55 to 59.9 lost 13.7 years.

"Our study further demonstrates that the expected number of years of life lost continued to increase for BMI values beyond 50 kg/m2, at which point the loss in life expectancy (9.8 y) exceeded that observed for current versus never smoking (8.9 y) in this study," Kitahara and colleagues wrote. "These results have great relevance to the current era, during which class III obesity rates have increased dramatically at the same time that smoking rates have declined."

Given the growing prevalence of class III obesity, the researchers said that extreme obesity may become a major cause of premature death in the U.S and other countries around the world.

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