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People battling diabetes — a disease known to trigger heart disease, kidney failure, blindness and nerve damage — now have another problem to worry about: colon cancer.

A series of recent studies is confirming an alarming link between the most common form of diabetes, known as type 2, and a significantly greater chance of developing cancer of the large bowel.

The surprising link is especially important to Southern Arizonans, who suffer some of the highest type 2 diabetes rates in the world, mostly among minorities.

Most affected are American Indians in this region, with the Tohono O'odham and Pascua Yaqui tribes have tenfold higher rates of this form of diabetes, while Hispanics face a doubled risk.

Type 2 diabetes — by far the most common form — is known as a "lifestyle" disease, triggered by obesity, poor diet and lack of exercise. Under such conditions, the body begins to produce insufficient insulin, the hormone that converts blood sugar into energy.

Some of the factors involved in type 2 diabetes — too much insulin in the blood, a high-fat diet, obesity, and chronic inflammation — are also risk factors for colon cancer, which may explain the link between the two killer diseases, experts say.

"We now know there is a definite likelihood that diabetes means an increased risk of colon cancer — that's valid," said Dr. Peter Lance, a specialist in the prevention of colon cancer at the University of Arizona Cancer Center.

"There's a great interest now in the effects of chronic inflammation, which is implicated in diabetes, heart disease and some cancers."

The most recent study of the issue compared colon cancer rates among nearly 2,000 type 2 diabetics to the general population, and found a significantly increased cancer risk in the diabetic group, most notably among men, and especially if they smoked.

"Colorectal cancer presents yet another serious health risk to diabetes sufferers," said Dr. Paul Limburg, a gastroenterologist at Mayo Clinic Cancer Center in Minnesota and lead author of the study, in a statement issued by the American Journal of Gastroenterology, which published the results in August.

"The need for all adults to follow a healthy diet, lifestyle and regular medical visits becomes even more important when considering that approximately one-third of persons with type 2 diabetes may not be aware of their diagnosis."

Nationwide, most diabetes experts estimate that more than 18 million Americans have diabetes, but 6 million don't know it. More than 145,000 Americans will be diagnosed with colon cancer this year, and more than 56,000 will die from it, according to the American Cancer Society.

In a larger study completed last year, data collected on 226,000 Americans during the National Health Interview Study found that the 6 percent with confirmed diabetes were 1.4 times as likely to develop colon cancer as non-diabetics.

Researchers involved in that study pointed to the elevated levels of insulin in the blood of diabetics as the possible reason. In laboratory studies, cells in the lining of the colon turn cancerous when exposed to high levels of insulin, they noted in a report to the American College of Gastroenterology.

Even so, doctors are not yet calling for increased colon-cancer screening for diabetics. But they are strongly warning these patients to follow screening guidelines recommended for all Americans.

Those guidelines say regular screening should start at age 50, with a stool blood test every year, or a flexible sigmoidoscopy every five years, or a colonoscopy every 10 years. However, anyone with a family history of colon cancer or inflammatory-bowel disease should be screened earlier and more often.

"At this time, we are not recommending any special screening for our diabetic patients, but we certainly insist they follow the guidelines that are out there now," said Dr. Douglas Spegman, an internist at El Rio Community Health Center, with a high patient population of diabetics.

Noting that a high-protein, high-fat diet puts a person at risk for both diabetes and colon cancer, Spegman said healthier eating is just as important as cancer screening.

"Is it just poor eating habits that explain the link between these two diseases? We don't know," he said. "But we do know that a better diet will lower both risks."