Women with type 2 diabetes have an 80% increased risk of colorectal adenoma compared with non-diabetics, a team from Washington University in St. Louis, Missouri, reported.
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.
The mean age of the diabetic group was 60 years, 41% were Caucasian, and 10% had a first-degree relative with colorectal cancer. Mean body mass index was 34.4, and 29% were on insulin.
The non-diabetic control group was comparable in hormonal status. The mean age was 59 years, 68% were Caucasian, mean BMI was 28.5 and 7% had a first-degree relative with colorectal cancer.
Any adenoma, or advanced adenoma that was either villous or tubulovillous and that was greater than 1 cm in size, or any high-grade dysplasia met the definition of adenoma in this study.
The rate of any adenomas was 37% among the diabetic women compared with 24% among the non-diabetics. This translated to an odds ratio of 1.80. Diabetics had a rate of advanced adenomas of 14% compared with 6% in non-diabetics, for an odds ratio of 2.4.
Obese women with diabetes had an odds ratio of 2.6 for any adenoma and 3.5 for advanced adenoma, compared with non-obese non-diabetics.
"Estrogen is known to affect the rate of colorectal cancer growth, so we controlled for estrogen status," Dr. Elwing pointed out in comments to Reuters Health.
As for the possible cause for the link between diabetes and colorectal adenoma, "hyperinsulinemia may be the reason," she said. "Insulin itself is a growth factor. It may have a direct pro-neoplastic effect, or it may act indirectly, through growth factor-1."
Digestive Disease Week 2006.