Impaired glucose tolerance tied to increased risk of cancer mortality

Impaired glucose tolerance, a known risk factor for diabetes and heart disease, may also increase the risk of cancer death.

For the estimated 15% of US adults with impaired glucose tolerance, the new findings provide yet another reason to modify a sedentary lifestyle, lead author Dr. Sharon H. Saydah told Reuters Health.”The finding may also explain why overweight people are more likely to develop cancer, especially colon cancer,” Dr. Saydah, from Johns Hopkins University in Baltimore, added. In a study of more than 3,000 adults followed between 1976 and 1980, she and her colleagues found that people with impaired glucose tolerance were nearly twice as likely to die from any type of cancer than were those with normal glucose levels. Their risk of dying from colon cancer, specifically, was more than quadruple that of healthy controls.After adjusting for age, sex and other factors associated with cancer risk, “abnormal glucose tolerance remained strongly associated with cancer mortality,” the researchers report in the June 15th issue of the American Journal of Epidemiology.The reason for the link is unclear. Previous reports have suggested that hyperinsulinemia may promote cancer development, since insulin has been shown to stimulate cell growth, especially colonic epithelial cells.However, people with overt diabetes were no more likely to die of cancer than were people with normal blood sugar levels. Again, the reasons are unclear, but Dr. Saydah offered several possible explanations.”As a person moves from normal glucose tolerance to impaired glucose tolerance to diabetes, their insulin levels increase rapidly and then gradually decline,” she said. This decline “may slow the cancer growth since there is not as much insulin or associated growth factors available for the cells.” Another potential reason, Dr. Saydah pointed out, is that given that cardiovascular disease is the leading cause of death among people with diabetes, it may be that people with diabetes have undiagnosed cancer and are simply dying from cardiovascular disease first.A third possibility, Dr. Saydah said, is that diabetes might offer some type of protective effect. “The theory behind this is that the blood vessels of individuals with diabetes are stiffer…possibly making it more difficult for cancer cells to spread throughout the body,” she explained.(Source: Am J Epidemiol 2003;157:1092-1100: Natalie Engler: Reuters Health: July 2, 2003: Oncolink)