Adults with extreme obesity have increased risks of dying at a young age from cancer and many other causes including heart disease, stroke, diabetes, and kidney and liver diseases, according to results of an analysis of data pooled from 20 large studies of people from three countries. The study, led by researchers from the National Cancer Institute (NCI), part of the National Institutes of Health, found that people with class III (or extreme) obesity had a dramatic reduction in life expectancy compared with people of normal weight. ÛÏWhile once a relatively uncommon condition, the prevalence of class III, or extreme, obesity is on the rise. In the United States, for example, six percent of adults are now classified as extremely obese, which, for a person of average height, is more than 100 pounds over the recommended range for normal weight,Û said Cari Kitahara, Ph.D., Division of Cancer Epidemiology and Genetics, NCI, and lead author of the study. In the study, researchers classified participants according to their body mass index (BMI). BMI classifications are:
- Normal weight: 18.5-24.9
- Overweight: 25.0- 29.9
- Class I obesity: 30.0-34.9
- Class II obesity: 35.0-39.9
- Class III obesity: 40.0 or higher
The 20 studies that were analyzed included adults from the United States, Sweden and Australia. After excluding individuals who had ever smoked or had a history of certain diseases, the researchers evaluated the risk of premature death overall and the risk of premature death from specific causes in more than 9,500 individuals who were class III obese and 304,000 others who were classified as normal weight. The researchers found that the risk of dying overall and from most major health causes rose continuously with increasing BMI within the class III obesity group. Deaths in the class III obesity group were mostly due to heart disease, cancer and diabetes. Years of life lost ranged from 6.5 years for participants with a BMI of 40-44.9 to 13.7 years for a BMI of 55-59.9.