Being overweight, underweight, associated with increased risk of death

Compared with normal weight, a person who is overweight or underweight has an increased risk of death, although that risk appears to have decreased in recent years for obesity, according to a study in the April 20 issue of JAMA.

As the prevalence of obesity increases in the United States, concern about the association of body weight and a higher risk of death has also increased, according to background information in the article.

Katherine M. Flegal, Ph.D., of the Centers for Disease Control and Prevention, Hyattsville, Md., and colleagues conducted a study to estimate deaths associated with underweight, overweight, and obesity in the United States in 2000 by using all available mortality data from the National Health and Nutrition Examination Surveys (NHANES). The researchers estimated relative risks of mortality associated with different levels of BMI (calculated as weight in kilograms divided by the square of height in meters) from the nationally representative (NHANES) I (1971-1975) and NHANES II (1976-1980), with follow-up through 1992, and from NHANES III (1988-1994), with follow-up through 2000. The authors then applied those relative risks to the NHANES 1999-2002 data to estimate excess mortality in 2000.

The researchers found that relative to the normal weight category (BMI 18.5 to less than 25), obesity (BMI 30 or greater) was associated with 111,909 excess deaths and underweight (BMI less than 18.5) with 33,746 excess deaths. Overweight was not associated with excess mortality. The relative risks associated with obesity were lower in NHANES II and NHANES III than in NHANES I.

"The differences between NHANES I and the later surveys suggest that the association of obesity with total mortality may have decreased over time, perhaps because of improvements in public health or medical care for obesity-related conditions. However, such speculation should be tempered by the awareness that these differences between surveys may simply represent chance variation and that small differences in relative risk translate into large differences in the numbers of deaths," the authors conclude.