While obesity has generally been viewed as a significant health concern, a Pitt study suggests that not all obese women share the same health risks.

This multicenter study of more than 90,000 women, published in the Journal of the American Medical Association July 5, shows extremely obese women to be at significantly higher risk of dying than women at normal weight and links the risk of death to specific categories of obesity.

To better quantify the health risks associated with obesity, the Pitt researchers, collaborating with researchers from six other institutions, examined the rates of death and of newly diagnosed coronary heart disease over a seven-year period of 90,185 women in five specific weight categories.

The women, all participants of the Women’s Health Initiative-Observational Study, were assigned to the weight categories based on the weight-to-height ratio known as body mass index (BMI): normal (BMI 18.5–24.9), overweight (BMI 25.0–29.9), obesity 1 (BMI 30.0–34.9), obesity 2 (BMI 35.0–39.9) and extreme obesity (BMI≥40).

The study showed that White women in the obesity 1 category (approximately 60 pounds above a normal weight for a 5-foot, 5-inch tall woman) to have a 12 percent higher risk of death over the seven-year followup period, but extremely obese women (approximately 110 pounds above a normal weight for a 5-foot, 5-inch tall woman) had an alarming 86 percent higher risk of death than their normal weight counterparts.

Death rates increased substantially with increasing weight category, ranging from 68.39 deaths per 10,000 person-years in women with normal BMIs to 116.85 deaths per 10,000 person-years in extremely obese women.

The study findings, according to lead author Kathleen McTigue, assistant professor of medicine and epidemiology in Pitt’s School of Medicine, suggest that the particularly rapid rise in extreme obesity in the United States may exacerbate the health effects and health-related expenditures of the ongoing obesity epidemic.

Although one of the national health objectives for the year 2010 is to reduce the prevalence of obesity among adults to less than 15 percent, current data indicate that the situation is worsening rather than improving, McTigue points out.

During the past 20 years, obesity rates among U.S. adults have skyrocketed, with 30 percent of adults 20 years of age and older—more than 60 million people—now categorized as obese and 9 million as severely obese. Over the past 25 years, the percentage of young people who are overweight or obese has more than tripled.

The prevalence of extremely obese women in the United States differs among racial and ethnic groups, with Asian Americans in this study having the lowest prevalence and African Americans having the highest.

The researchers found no difference in the weight-related risk for death from all causes, death due to heart disease, and new onset of heart disease across the diverse racial and ethnic groups, although they point out that the relatively small number of women from certain racial/ethnic groups limited their ability to examine these outcomes within all groups in detail.

The investigators also examined African American and Caucasian women more closely, finding that both groups experienced increased risks of mortality and new onset of coronary heart disease with increasing weight category. In addition, the risk for diabetes and hypertension increased as excess weight became more extreme, and even women who were overweight but not obese experienced significant weight-related health consequences.

According to McTigue, these results suggest that degree of obesity has a major impact on health risk.

“When a woman and her physician are choosing treatment options for obesity, they should carefully consider the degree of obesity, not just think of obesity as an overall entity,” she said. “The degree of obesity will influence how likely it is that her health will be harmed by her current weight. These findings also underscore the importance of learning more about the best treatments for extremely obese women, as well as the need for aggressive diagnosis and treatment of diabetes, high blood pressure, and high cholesterol in the obese.”

The study was funded in part by the National Institute of Diabetes and Digestive and Kidney Diseases.