Diabetes may significantly increase a woman's risk of developing colorectal cancer, based on the findings of a study involving more than 45,000 women across the United States.
“There was about a 50% increased risk of colorectal cancer in women with diabetes,” said Andrew Flood, Ph.D., a professor of epidemiology and community health at the University of Minnesota in Minneapolis.
Dr. Flood presented study findings at a press briefing held in conjunction with the annual international conference of the American Association for Cancer Research. He and his colleagues prospectively analyzed data from the Breast Cancer Detection Demonstration Project follow-up cohort study.
From 1987 to 1989, 45,519 women without a history of colorectal cancer completed a series of questionnaires that assessed dietary and other health and lifestyle risk factors for colorectal cancer. The average age at the time of the interview was 62 years. On average, the time between the baseline and follow-up was 9 years, during which time 489 women developed colorectal cancer. After the researchers controlled for age, physical activity, energy intake, alcohol consumption, hormone therapy, smoking, multivitamin use, education, ethnicity, NSAID use, calcium supplementation, and calcium intake from diet, women with diabetes at baseline had an adjusted hazard ratio (HR) of 1.50 for developing colorectal cancer.
The researchers hypothesized that the elevated levels of insulin typically seen in people with type 2 diabetes may play a central role. Insulin stimulates the growth of normal colonic and carcinoma cells. Insulin also modulates insulin-like growth factor 1 (IGF-1) and its binding proteins, creating a promitotic environment for colonic epithelial cells.
When the researchers conducted a second analysis that included women who were likely prediabetic at baseline, according to self-reports at the 1993–1995 follow-up, the multivariate adjusted HR for developing colorectal cancer was slightly lower (1.36) in this population of women.
Among the prediabetic women, the degree of hyperinsulinemia may not have been of a sufficient magnitude or duration to increase the risk of colorectal cancer, the researchers speculated. Or there may be some factor related to diabetes, independent of hyperinsulinemia, that is driving the observed increase in colorectal cancer risk among the diabetic women.