As increasing numbers of Americans become more obese than ever before, mortality and health-expenditure estimates may need to be revised to reflect the fact that as obesity levels rise, so does the risk of dying or developing coronary heart disease. Researchers writing in the July 5, 2006 issue of the Journal of the American Medical Association report that women with "extreme obesity" (BMI >40) have a greater mortality risk than women with lesser degrees of obesity [1].

"Considering obesity as a homogenous condition with fixed risk is inappropriate," Dr Kathleen McTigue (University of Pittsburgh, PA) et al write. "Weight-related health risk clearly varies with degree of excess weight."

As McTigue et al note, "obesity" refers to a BMI of 30 or greater; however, it can also be further defined by category—obesity 1 (BMI 30-34.9), obesity 2 (35-49.9), and obesity 3 (>40). "The latter two, sometimes termed severe obesity, are reported to be increasing, especially rapidly in the US," McTigue et al write.

For their study, McTigue et al used data from more than 90 000 women, aged 50 to 79 years, participating in the Women's Health Initiative—Observational Study. Event rates were tracked over a seven-year period.

Overall deaths, expressed as rate per 10 000 person-years, was 68.39 for normal-weight women—similar to that of overweight women. These rates, however, continued to increase across all three levels of obesity and were highest among the women with extreme obesity.

Extreme obesity was most common among black women (10% of the study population) and Native Americans (7.9%), and lowest among Asian and Pacific Islanders (1%). Across racial groups, obesity-related mortality and cardiovascular disease was mediated by diabetes, hypertension, and hyperlipidemia.

"The escalating prevalence of extreme obesity may exacerbate the health effects and health-related expenditures resulting from the US obesity epidemic," McTigue et al write. "Calculating the weight-related risks of morbidity and mortality based on findings in earlier population samples, which tended to reflect lower degrees of obesity, may underestimate the risks for extremely obese individuals and overestimate the risks for mildly obese individuals in diverse groups."

By taking into account the varying degree of risk associated with different categories of obesity, clinicians and policy-makers might be better able to tailor therapies and understand risk levels, they conclude.