Flegal and colleagues used nationally representative data from NHANES I, II, and III and follow-up data collected through 2000 to estimate the number of excess deaths in 2000 associated with body mass index (BMI), categorized as underweight, normal weight, and obese. They found that compared with normal weight, both underweight and obesity were associated with increased mortality, and the risk associated with obesity declined over time.

People who are overweight but not obese have a lower risk of death than those of normal weight, US federal researchers are reporting today.

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 (The Journal of the American Medical Association).

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.

CARDIOVASCULAR RISK FACTORS HAVE DECLINED SUBSTANTIALLY OVER PAST 40 YEARS

Prevalence of high cholesterol levels, hypertension and smoking, particularly among overweight and obese adults, have declined considerably over the past 40 years, according to a study in the April 20 issue of JAMA. This trend was not true for diabetes, which has had a stable prevalence.

The association between the increase in obesity in the U.S. population and cardiovascular disease (CVD) risk factors has been uncertain. according to background information in the article.

Edward W. Gregg, Ph.D., of the Centers for Disease Control and Prevention, Atlanta, and colleagues analyzed data from 5 NHANES conducted during the last 40 years and examined whether long-term changes in levels of key cardiovascular risk factors have been different in overweight or obese persons compared with lean persons. The risk factors included prevalence of high cholesterol levels (240 mg/dL or greater [6.2 mmol/L or greater] regardless of treatment), high blood pressure (140/90 mm Hg or greater regardless of treatment), current smoking, and total diabetes (diagnosed and undiagnosed combined) according to BMI group (lean, less than 25; overweight, 25-29; and obese, 30 or greater).

The researchers found: "In this unique series of nationally representative surveys of the U.S. adult population, we documented a substantial decline in the prevalence of key CVD risk factors over the last 3 to 4 decades, affecting obese, overweight, and lean segments of the population. Among obese persons today, prevalence of high cholesterol, high blood pressure, and smoking are now 21, 18, and 12 percentage points lower, respectively, than among obese persons 30 to 40 years ago. The corresponding reductions among lean persons have been somewhat less, with average declines of 12 to 14 percentage points. Although obesity remains associated with a higher prevalence of important CVD risk factors, differences in total cholesterol levels across BMI groups may be narrowing, and for blood pressure and smoking improvements have been similar across BMI groups. Thus, obese and overweight persons may be at lower risk of CVD now than in previous eras."

"Diabetes is a notable exception to the observed reduction in risk factors, as prevalence of total diabetes (i.e., diagnosed and undiagnosed combined) did not decrease within BMI groups. This was accompanied by a 55 percent increase in total diabetes among the overall population (i.e., all BMI groups combined), presumably due to an increasing proportion of the population moving into the obese categories," the authors write.

"Despite our encouraging findings, a considerable proportion of lean as well as obese persons still have elevated levels of modifiable risk factors, particularly when one considers that the current definitions of risk factor control are more aggressive than the definitions used in this trend analyses. Clinical and public health efforts should continue to emphasize maintenance of healthy lifestyle behaviors for both lean as well as overweight and obese persons," the authors conclude. 

EDITORIAL: DEATHS ATTRIBUTABLE TO OBESITY

In an accompanying editorial, David H. Mark, M.D., M.P.H., Contributing Editor of JAMA, Chicago, discusses the two studies in this week's JAMA that examine weight and health.

"These studies...highlight the importance of continuing to develop more rigorous approaches for estimating obesity-attributable deaths. Ultimately, though, it may be possible to gain a better and more realistic understanding of the preventable disease burden caused by obesity by evaluating public health and individual programs designed to both prevent and treat obesity, such as diet and exercise programs."

"Such programs should also be evaluated for their ability to reduce disease and morbidity in addition to effects on body weight, for there may be additional benefits (or possible risks). With sufficient knowledge of the effectiveness and required resources of these programs, it will be possible to make rational decisions regarding the best way to maintain and improve the health of the public," Dr. Mark concludes.