Women with type 2 or non-insulin dependent diabetes have an 80 percent increased risk of developing colorectal adenomas - growths or polyps that can become cancerous, a team from Washington University in St. Louis, Missouri, reported here at Digestive Disease Week 2006.

Also, diabetes plus obesity more than doubles the risk of colorectal adenomas, and of adenomas found at more advanced stages, compared with the risk in non-obese non-diabetic women.

Dr. Jill E. Elwing and colleagues studied 100 women with type 2 diabetes and 500 non-diabetic women who were undergoing screening colonoscopy.

They observed that the rate of any adenomas was significantly higher in the diabetic women compared with that in the non-diabetic women - 37 percent versus 24 percent. The rate of advanced adenomas was also much higher in diabetic women compared with non-diabetic women - 14 percent versus 6 percent.

Compared with non-obese non-diabetic women, obese diabetic women had a more than twofold higher likelihood for any adenoma and a more than threefold higher likelihood for advanced adenoma.

“Estrogen is known to affect the rate of colorectal cancer growth, so we controlled for estrogen status,” Elwing pointed out in comments to Reuters Health.

As for the possible cause for the link between diabetes and colorectal adenoma, abnormally high insulin levels “may be the reason,” she said. Insulin itself is a growth factor, she explained and it may have a direct pro-cancerous effect, or it may act indirectly, through growth factors.