Wide Waists Boost Mortality Risk

People with excess weight have increased health risks, doctors have long known. But now a new study suggests that even people in the normal weight range for their heights have increased risks, too, if their waists are wide.

Having a large waist has been tied to health problems before, but the results of previous studies have been inconsistent. It wasn't clear if waist circumference could give doctors any more information than body mass index (BMI—a ratio of weight to height) could.

Dr. Annemarie Koster at NIH's National Institute on Aging (NIA) set out to look at the question more closely by studying a large group of people. The research team used data from the NIH-AARP Diet and Health Study, which was supported by NIH's National Cancer Institute (NCI) and AARP, to examine BMI and waist circumference data from almost 155,000 men and over 90,000 women who were 51–72 years old at the beginning of the study. They assessed mortality over 9 years of follow-up.

As reported in the June 2008 issue of the American Journal of Epidemiology, after adjusting for BMI and other factors, the researchers found that people with the largest waist circumferences had a significantly higher mortality risk than those with smaller waists. The relationship held in people with and without disease, in smokers and nonsmokers, and across different racial/ethnic groups.

The large numbers of people in the study allowed the researchers to tease apart the effects of BMI and waist circumference. They found that people with a normal BMI but a large waist circumference—for men, 40 inches or more; for women, 35 inches or more—had about a 20% higher mortality risk than people whose BMI and waist circumference were both in the normal range.

"People not only should look at their weight but also consider their waist," Koster said. "You can have what's considered a healthy BMI but also have a large waist circumference and have an increased mortality risk."

Koster noted that future work needs to focus on specific race and ethnic groups. There was some evidence in the study, for example, that Asian people might have a higher mortality risk at smaller waist circumferences than others, but this has to be confirmed in a study with larger numbers of Asian people.

Future work, Koster said, also needs to look more closely at the relationship between fat, or adipose tissue, and mortality. "Waist circumference is a proxy for abdominal adipose tissue," she said. Why having more adipose tissue raises your health risks is still not well understood.

—by Harrison Wein, Ph.D.