Class 3 obesity is linked to substantially increased death rates, according to a new study conducted by the National Cancer Institute.
Otherwise known as "extreme obesity," class 3 obesity has increased more than 10-fold in the US since the mid-1980s, and currently affects 6% of the American adult population. People in this group also accounted for 20% of the total per capita health care expenditures in 2000.
However, because class 3 has been uncommon until relatively recently, studies have only had limited sample sizes with which to measure the effects on mortality of this kind of obesity.
In this new study, researchers from the National Cancer Institute examined data from 20 prospective studies involving the National Cancer Institute Cohort Consortium, which took place in the US, Sweden and Australia.
Because class 3 has been uncommon until relatively recently, studies have only had limited sample sizes with which to measure the effects on mortality of this kind of obesity.
The researchers excluded participants who had previously smoked or who had a history of chronic disease, which left them with 9,564 adults who were classified as being class 3 obese, and 304,011 adults of a normal weight. The participants were followed for a total of 30 years.
The analysis shows that the mortality rates (deaths per 100,000 persons per year) were 856 for class 3 obese men and 663 for class 3 obese women. By contrast, the mortality rates for normal-weight men and women were 346.7 and 280.5, respectively.
In the class 3 obese participants, heart disease was found to be the major factor influencing the higher mortality rate, followed by cancer and diabetes. The risk of death from these and other diseases also increased with increasing BMI.
The researchers calculated that, compared with having a normal weight, having a BMI between 40 and 59 kg/m2 results in an estimated loss of 6.5-13.7 years of life.
But the authors say that - as the studies were only conducted in three countries - the findings may not apply to all populations. Also, because they used self-reported height and weight to calculate BMI - and did not use any other measures of obesity - the researchers cannot verify that the calculations were completely accurate.
Despite this, the authors believe that their results demonstrate a link between class 3 obesity and a substantially increased mortality rate. They write:
"Class III obesity is associated with excess rates of total mortality and mortality due to a wide range of causes, particularly heart disease, cancer, and diabetes, and that the risk of death overall and from these specific causes continues to rise with increasing values of BMI.
We found that the reduction in life expectancy associated with class III obesity was similar to (and, for BMI values above 50 kg/m2, even greater than) that observed for current smoking."
Yesterday, Medical News Today reported on a study by Stanford University researchers that found the rise in obesity across the US is caused more by increasingly sedentary lifestyles than an increase of people eating too many calories.
We also recently reported on a study from researchers in Ireland and the UK, which suggested that TV sets children a "bad example" on food, which is "not helpful" in a society where obesity is becoming increasingly prevalent.