middle aged woman looking concerned

More than 25 million adults aged 20 and older in the United States have diabetes. That figure has more than tripled since 1980. That is bad news for a number of reasons. Not only can diabetes cause heart disease, stroke, nerve damage, and eye issues, but recent research now shows there is also a clear link between type 2 diabetes and colon cancer.

Colon cancer is one of the most preventable types of cancer, yet it is still the third most common cancer among both men and women in the U.S. And, many of the ways people can lower their risk for colon cancer are actually the same as how they can avoid developing type 2 diabetes. These include:

  • Staying away from a diet high in red and processed meats
  • Keeping physically active
  • Maintaining a healthy weight
  • Staying away from tobacco
  • Avoiding heavy alcohol use

Even though the two diseases share several common risk factors, research shows that type 2 diabetes itself is indeed linked to increased risk of developing colon cancer. Studies also show that among patients diagnosed with colorectal cancer, those with diabetes were more likely than those without it to die – even after controlling for other factors such as disease stage, body weight, and smoking habits.

There are a few major hypotheses for the link, according to Peter Campbell, Ph.D., an American Cancer Society researcher who has been studying the connection between diabetes and colon cancer for a number of years.

One idea has to do with a condition that causes the amount of insulin in a person’s blood to be higher than normal, called hyperinsulinemia. Insulin is the body’s way of regulating the amount of sugar – or glucose – in the blood. Hyperinsulinemia can lead to the development of type 2 diabetes. The thought, says Campbell, is that the abnormally high levels of insulin and glucose create an environment in the colon that promotes the development and growth of cancer.

Other working theories have to do with untreated hyperglycemia – the condition of having too much sugar in the blood – and chronic inflammation due to diabetes. Campbell says researchers seem to have ruled out the idea that it is the injected insulin that people with type 2 diabetes sometimes have to use to treat their condition that is linked to colon cancer. Rather, the cancer risk appears to have something to do with type 2 diabetes itself.

However, much more research is needed to discover exactly why type 2 diabetes appears to increase a person’s risk for colon cancer – and other cancers as well. Diabetes is also linked with increased risk of dying from pancreas, breast, and liver cancers.

In particular, Campbell says researchers want to further study whether other type 2 diabetes drugs have any effect on colon cancer risk, the “underlying molecular basis for the link” between diabetes and colon cancer, and the role of type 2 diabetes after a person is diagnosed with colorectal cancer. He also wants to investigate whether improvements in blood sugar control could lower the risk of colon cancer for those with type 2 diabetes. Campbell plans to try to answer these questions by studying people enrolled in the American Cancer Society’s new long-term follow-up study – Cancer Prevention Study-3 (CPS-3).