The researchers pooled data from 11 different cohort studies, including more than 600,000 people from around the world. They found that men with waists 43 inches or greater in circumference had a 50 percent higher mortality risk than men with waists less than 35 inches, and this translated to about a three-year lower life expectancy after age 40. Women with a waist circumference of 37 inches or greater had about an 80 percent higher mortality risk than women with a waist circumference of 27 inches or less, and this translated to about a five-year lower life expectancy after age 40.
Importantly, risk increased in a linear fashion such that for every 2 inches of greater circumference, mortality risk went up about 7 percent in men and about 9 percent in women. Thus, there was not one natural "cutpoint" for waist circumference that could be used in the clinic, as risk increased across the spectrum of circumferences.
Another key finding was that elevated mortality risk with increasing waist circumference was observed at all levels of BMI, even among people who had normal BMI levels. Because of the large size of this pooled study, researchers were able to clearly show the independent contribution of waist circumference after accounting for BMI, says James Cerhan, M.D., Ph.D., a Mayo Clinic epidemiologist and lead author of the study.
"BMI is not a perfect measure," says Dr. Cerhan. "It doesn't discriminate lean mass from fat mass, and it also doesn't say anything about where your weight is located. We worry about that because extra fat in your belly has a metabolic profile that is associated with diseases such as diabetes and heart disease."
Dr. Cerhan says physicians should consider both BMI and waist circumference as part of risk assessment for obesity-related premature mortality.
"The primary goal should be preventing both a high BMI and a large waist circumference," Dr. Cerhan says. "For those patients who have a large waist, trimming down even a few inches — through exercise and diet — could have important health benefits."
This study was funded by the U.S. National Cancer Institute as part of the Cohort Consortium and included investigators from North American, Europe and Australia.
-Mayo Clinic News Network