A new study, published in PLOS Medicine, looked at the association between extreme obesity and mortality. Collecting data from 20 prospective studies, the research team conducted a pooled analysis. Extreme obesity was correlated with an increased risk of premature death similar to that of smoking in people of a normal weight. Premature death related to obesity was largely due to related conditions such as heart disease, diabetes, and cancer.

Extreme obesity is technically known as class III, which includes individuals that have a body mass index (BMI) of 40 to 59.9. Currently, six percent of the U.S. population suffers from extreme obesity. Around the world, the prevalence of class III obesity has been on the rise. Controlling for other lifestyle factors, extreme obesity still had a significant, detrimental impact on life expectancy.

The Los Angeles Times reports that the extremely obese are those that need to lose 100 pounds or more in order to reach a healthy weight status. Since the 1980s, the population that has a BMI of 40 or higher has grown fourfold and the population with a BMI of 50 or higher has grown by 10 percent. In addition to life expectancy costs, the medical costs for these individuals amount to approximately one-fifth of all healthcare dollars spent in the U.S.

To calculate BMI, the National Institutes of Health (NIH) offers an online BMI calculator. The measurement is based on height and weight. A normal weight is 18.5 to 24.9, overweight is 25 to 29.9, and obesity is 30 and above. Though the BMI is not the ideal measurement for all scenarios, it is easy to calculate and track.