People with both Type 1 and Type 2 diabetes appear to be at higher risk of developing certain types of cancer—but as to why it exists, there is still some dispute.1
One possibility is that using insulin over long periods of time may play a role in developing a risk for cancer.2,3 However, the numbers seem to be telling a different story, according to a Jessica L. Harding, a PhD candidate from the Baker IDI Heart and Diabetes Institute in Melbourne, Australia, coauthor of a new study in Diabetes Care.4
Harding said her research supports a different idea – "that the relative risk for cancer is similar among people with Type 1 and Type 2 diabetes." Since insulin resistance and excess insulin (hyperinsulinemia) are more common with Type 2 diabetes, the numbers should have been more affected by the type of diabetes.
So, perhaps it's not insulin that's causing cancer. Maybe it's high blood glucose (hyperglycemia) that damages the body over time.
"People with type 1 and type 2 diabetes differ markedly in their insulin exposure, but are similar in terms of hyperglycemia," Harding said. "It is certainly biologically plausible that long-term exposure to high blood glucose could damage cells and result in the development of cancer."
However, research is still lacking to prove this. Large trials have looked at lowering blood glucose in people with diabetes, but haven't seen any noticeable results in terms of lowering the risk of developing cancer, she said.
"Future studies are definitely needed to tease out these associations before we can establish cause and effect," Harding said. There are also the challenges of finding quality data to conduct these kinds of studies.
The researchers looked at nearly a million registrants in Australia's National Diabetes Service Scheme (NDSS) database. Diagnosed between 1997 and 2008, 80,676 (8.5%) of those registrants had type 1 diabetes, while the rest, 872,706 (91.5%), had type 2 diabetes. After comparing the NDSS data with Australian cancer rates found in the general population, they found people with diabetes had higher rates of certain types of cancer.
Compared to the general population, women with Type 1 diabetes showed a higher risk for cancers associated with various organs in the digestive system, like the liver, pancreas, esophagus, stomach, colon, and rectum, as well as the brain, lung, thyroid, ovaries, and endometrium. Men had similar associations, including high mortality ratios for cancers of the pancreas, liver, kidney, and non-Hodgkin's lymphoma. Researchers also found decreases in risk for certain cancers, where women had a decreased risk of melanoma cancer and men had a decreased risk of prostate cancer.
People with Type 2 diabetes also showed an increased risk for all kinds of cancers, especially in the liver and pancreas. Brain and testicular cancers were an exception, and women did not have a higher risk for anal or esophageal cancer. Also, a decreased risk was found for melanoma and prostate cancers similar to Type 1 patients. Females had high mortality ratios in gallbladder, stomach, and non-Hodgkin's lymphoma cancers, while men's were observed with liver, pancreas, kidney, and Hodgkin’s lymphoma cancers.
Harding, et al.'s study was funded by the NHMRC, Australian Government Department of Health and Ageing and supported in part by the Victorian Operational Infrastructure Program scheme. The authors reported no conflicts of interest.