July 8, 2003

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Pre-Diabetic Adults at Increased Risk of Colon Cancer

People with impaired glucose tolerance (IGT), a precursor to diabetes, are at increased risk of dying from colon and other cancers, according to a study directed by Johns Hopkins researchers.

Results of the study, published recently in the American Journal of Epidemiology, show that those with IGT are nearly twice as likely to die from any cancer and more than four times as likely to die from colon cancer as those with normal glucose tolerance.

"By contrast, adults with outright diabetes had little or no association with risk of cancer death," says senior study author Frederick L. Brancati, M.D., associate professor of medicine and epidemiology at Johns Hopkins.

The exact mechanism underlying the apparent increased risk is not clear, Brancati says, although previous studies suggest that high levels of insulin, which is a biologic growth factor, may promote the development of cancer cells.

IGT, present in about 15 percent of American adults, is defined as blood sugar levels that are higher than normal but not high enough to be classified as diabetes. One-third of people with IGT develop diabetes within five years. Although there are no proven methods for IGT prevention, Brancati says, most people with the condition are overweight and sedentary, so losing weight and increasing physical activity would likely help.

For the study, Brancati and colleagues studied data from 3,054 adults ages 30 to 74 who underwent glucose tolerance testing as part of the Second National Health and Nutrition Examination Survey (NHANES II) Mortality Study. This long-term study of adults offered physical exams, laboratory tests, and questionnaires on health and nutrition-related topics, beginning in the years 1976 to 1980. Study participants were classified as having either diagnosed diabetes (247 adults), undiagnosed diabetes (180 adults), impaired glucose tolerance (477 adults) or normal glucose tolerance (2,250 adults). Those who had cancer at the study's start were excluded.

Compared with participants having normal glucose tolerance, those with IGT were older and more likely to be female, less educated and sedentary. They also were less likely to be current smokers or to drink one or more alcoholic drinks per week. In addition, they had greater body fat, lower high-density lipoprotein or "good" cholesterol, and higher total cholesterol, triglycerides and blood pressure.

Researchers confirmed deaths in the study groups occurring between 1976 and 1992 by searching the national death index and Social Security Administration Death Master File.

Of 737 deaths that occurred during the study period, 206 (28 percent) were from cancer. The IGT group had the highest cancer death rate, followed by those with undiagnosed diabetes, diagnosed diabetes, and those with normal glucose tolerance. After researchers adjusted for lifestyle and other factors, they found that participants with IGT were 1.87 times more likely to die from cancer than their healthier counterparts. The most commonly reported cancer sites were lung, colon, pancreas, breast and prostate. In addition, IGT participants were 4.24 times more likely to die of colon cancer than their healthier counterparts.

The study was supported by grants from the National Heart, Lung and Blood Institute and the American Heart Association. Co-authors were Sharon H. Saydah and Mark S. Eberhardt of the Centers for Disease Control and Prevention, and Catherine M. Loria of the National Heart, Lung and Blood Institute. Saydah was a doctoral student at Johns Hopkins at the time the study was completed.

Saydah, Sharon H. et al, "Abnormal Glucose Tolerance and the Risk of Cancer Death in the United States," American Journal of Epidemiology, June 15, 2003; Vol. 157, pages 1092-1100.

Related Links:

Johns Hopkins' Welch Center for Prevention, Epidemiology and Clinical Research

American Journal of Epidemiology



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