Type 2 Diabetes Raises Risk of 24 Cancers

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For reasons that scientists do not yet understand, people who have type 2 diabetes are at increased risk for developing 24 types of cancer that were examined as part of a new research study. Because of the high prevalence of type 2 diabetes, a better understanding of this relationship will have far-reaching implications.

According to the National Diabetes Fact Sheet for 2007, which is the most recent year for which data are available, 23.6 million people in the United States have diabetes: 17.9 million diagnosed and 5.7 million undiagnosed. Another 57 million are believed to have pre-diabetes, which means they are likely to develop type 2 diabetes within a few years. Worldwide, diabetes affected 246 million people in 2006.

People who have diabetes are known to be at increased risk for other health complications. For example, adults with diabetes have heart disease death rates 2 to 4 times greater than adults without diabetes, and their risk for stroke is also 2 to 4 times higher. Diabetes is also the leading cause of kidney failure and the leading cause of new cases of blindness among adults aged 20 to 74. About 60 to 70 percent of people with diabetes have mild to severe forms of nervous system damage as well.

The new study, which was conducted by the German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) in collaboration with researchers in Sweden and the United States, evaluated data from 125,126 Swedish citizens who had been in the hospital for problems related to type 2 diabetes. The incidence of cancer among these patients was compared with that of the general population in Sweden.

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Data for the study was gathered from a registry that followed every hospital release in Sweden from 1964 to 2007. These data were combined with the Swedish National Family Cancer Database, which records all cases of cancer in Sweden since 1958.

The comparison showed that people with type 2 diabetes have an increased risk of developing 24 different types of cancer among those the epidemiologists explored. The greatest risks were for pancreatic cancer (sixfold increased risk) and liver cell cancer (4.25-fold risk). Cancers that posed more than twice the risk were those that affect the kidneys, thyroid, esophagus, small intestine, and the nervous system.

A curious finding was that people with type 2 diabetes have a significantly lower rate of prostate cancer, which was especially obvious in patients who had a family history of the disease. Kari Hemminki of DKFZ commented that “a lower level of male sex hormones in diabetics may be among the factors that are responsible for this.”

To rule out the possibility that cancer rates among type 2 diabetics were higher because the cancers were found as a result of hospitalization, the researchers analyzed how many cancers had occurred in the participants after one and five years, respectively, after their hospitalizations. The trend was essentially the same.

The increased risk of cancers among people who have type 2 diabetes is a significant finding. Given that both type 2 diabetes and cancer are major health challenges that have a dramatic impact on quality of life and the health care system, this relationship warrants more investigation.

SOURCES:
American Diabetes Association
German Cancer Research Center

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