Diabetes again linked to colon cancer risk: study

People with diabetes have a somewhat increased risk of colon cancer, an international study said - but the reasons for the connection, and what should be done about it, remain unclear.

Researchers headed by Hiroki Yuhara, at the University of California, Berkeley, combined the results of 14 international studies and found that, overall, people with diabetes were 38 percent more likely to be diagnosed with colon cancer than those who were diabetes-free.

There was also a 20 percent increase in the risk of rectal cancer, though that appeared to be confined to men, according to the findings, published in the American Journal of Gastroenterology.

"These data suggest that diabetes mellitus is an independent risk factor for colon and rectal cancer," Yuhara and his colleagues wrote.

The findings do not prove that diabetes directly contributes to colon cancer in some people.

The results come from observational studies in which people with diabetes were found to have a higher risk of colon cancer than those without diabetes. In most of the studies, the researchers adjusted for at least some factors that might explain the link - like older age, obesity and smoking - and the diabetes-cancer connection remained.

"I think we can make the statement that diabetes is consistently associated with colorectal cancer," said Edward Giovannucci of the Harvard School of Public Health, who was not involved in the study.

"The cause-and-effect aspect is a bit difficult to consider since diabetes is such a complex disease," he told Reuters Health in an email.

Impact of Diabetes on Colon Cancer Risk

A study published in the Journal of the National Cancer Institute examined data from more than two million colorectal cancer patients to determine the impact of diabetes on colon cancer risk. The researchers reported that diabetics have a 20-40% increased risk of developing colon cancer.

Other studies have determined that people with diabetes have a 60% increased risk of developing colon cancer. The actual percentage increase may not be that clear, but the take-home message is: if you have diabetes, you're at increased risk for colon cancer

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He said it seems likely that some aspect of diabetes contributes to colon cancer, but it's not certain what.

One theory is that hormones are involved.

People with Diabetes tend to have high levels of the blood-sugar-regulating hormone insulin, as well as related hormones called insulin-like growth factors. Those hormones cause cells to grow and spread, and that may include cancer cells.

Impact of Diabetes on Colon Cancer Recurrence and Survival