Being overweight during midlife is associated with an increased risk of death, according to a new study conducted by the National Cancer Institute (NCI), part of the National Institutes of Health, in collaboration with AARP, the nation's leading organization for persons 50-Plus. Results of the study appear in the August 24, 2006, issue of the New England Journal of Medicine.
Previous research had established a link between obesity and increased risk of death, but whether a relationship also existed between being overweight and increased risk of death remained uncertain. In 2004, the Centers for Disease Control and Prevention (CDC) reported that 34.1 percent of the U.S. adult population was overweight, but not obese**. Overweight and obesity are defined using a measurement called body-mass index (BMI), calculated as a person's weight divided by the square of their height. A BMI of 18.5 - 25.0 is considered normal, whereas people who have a BMI of 25.0 - 29.9 are considered overweight, and individuals with a BMI over 30.0 are regarded as obese. (Click to view BMI chart)
The NIH-AARP Diet and Health Study of 527,265 monitored the health status of Americans from 1995 through 2005 via mailed questionnaires and by surveying death records. When the analysis focused on BMI at age 50 among persons who had never smoked, the researchers, led by Kenneth F. Adams, Ph.D., of NCI's Division of Cancer Epidemiology and Genetics, found that the risk of mortality among participants who were overweight increased by 20 to 40 percent. Mortality risk among obese participants increased two to three-fold.
"BMI at age 50 gives a more accurate representation of the amount of excess fatness a person was exposed to over decades," said Michael F. Leitzmann, M.D., NCI, senior author of the study. "On the other hand, body weight reported at age 65, for example, might reflect a recent weight loss due to cancer or other disease. If that person then dies the next year, it would be inaccurate to classify that person in the normal BMI range when their pre-cancer BMI was actually overweight."
The study enrolled over half a million participants ages 50-71 years. "AARP members recognize the importance and value of health research," said Albert R. Hollenbeck, Ph.D., a senior research advisor with the organization in Washington, D.C. "That is why AARP actively helped recruit over 500,000 men and women from our membership base for this study."
Some earlier studies have shown that being overweight was not associated with an increased risk of death. However, smoking and chronic illness are associated with a lower BMI and an increased risk of death, which may distort the relationship between BMI and mortality.
An advantage of the current study was the availability of data on more than 186,000 male and female participants who had never smoked. This allowed the researchers to untangle the complex relationships between body weight, smoking, existing disease, and risk of death. Other possible confounding factors that were accounted for included age, race or ethnic group, level of education, physical activity, and alcohol intake.
Since pre-existing chronic disease can lead to weight loss, this study also included alternative analyses that disregarded deaths occurring soon after enrollment and restricted the assessment to groups without pre-existing disease. In addition, the researchers adjusted for pre-existing disease by asking older participants to report their weight as it was when they were 50 years old. Examining weight at an earlier age provides a measure of typical adult weight that is largely unaffected by the onset of chronic disease.
Excess body weight is known to increase the risk of heart disease, stroke, high blood pressure, pulmonary disease, and diabetes. Furthermore, a recent study suggested that increased body weight is related to an elevated risk of mortality from cancer.
"Any associations between mortality and being overweight have important clinical and public health implications, including risk of cancer. Tackling this public health problem could make an important difference in reducing cancer rates," said NCI Director John E. Niederhuber, M.D.
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