In the final study of 73,312 men and 81,663 women, 1,567 men (227 with type 2 diabetes) and 1,242 women (108 with type 2 diabetes) were diagnosed with colon or rectal cancer by 2007. Among men, type 2 diabetes was associated with increased risk of incident CRC compared to not having type 2 diabetes. CRC risk was higher for those participants with type 2 diabetes regardless of whether or not they used insulin.

Among women, type 2 diabetes and insulin use were not associated with CRC risk. These findings support recent observations that the association may be more prominent in men than in women, and raise the possibility of a stronger association among individuals with a family history of CRC. This finding could have clinical relevance if confirmed by other large studies. The authors speculate that the lack of an association between type 2 diabetes and CRC risk among women might relate to improved glucose control among women with type 2 diabetes in recent years.

Participants were selected from the Cancer Prevention Study II Nutrition Cohort, a prospective study of cancer incidence. In 1992 or 1993, 184,194 adult participants completed a detailed, self-administered questionnaire. Follow-up questionnaires were sent in 1997 and every two years thereafter.

Source: American Gastroenterological Association