CHICAGO—Obesity is dangerous, but it may not be as life threatening as health professionals once thought.

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 by researchers at the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health. Published in the April 20 issue of Journal of the American Medical Association, the researchers found that relative to the normal weight category (a BMI of 25 to 18.5), obesity (a BMI 30 or greater) was associated with 111,909 excess deaths and underweight (a BMI less than 18.5) with 33,746 excess deaths. Overweight was not associated with excess mortality. This data is much lower than the highly publicized figure released in March 2004 when other CDC researchers estimated that about 400,000 deaths were associated with obesity, poor diet and inactivity. Later, that number was lowered to 365,000 when problems with calculations were found. Authors say the numbers are lower because data was different and more recent.

"The differences between NHANES I (National Health and Nutrition Examination Surveys) 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.

Lead author Katherine M. Flegal of the CDC and colleagues conducted the study to estimate deaths associated with underweight, overweight and obesity in the United States in 2000 by using all available mortality data from the NHANES. Researchers estimated the relative risks of mortality associated with different levels of BMI from the nationally representative data from the first NHANES from 1971 to 1975 and the second NHANES from 1976 to 1980, with follow-up through 1992, and lastly from the third NHANES from 1988 to 1994, with follow-up through 2000. The researchers then applied those relative risks to the NHANES 1999-2002 data to estimate excess mortality in 2000.