Evidence indicates a modest increase in risk of bowel cancer among people with type 2 diabetes

For two decades, investigators have recognised the overlapping risk factors for type 2 diabetes mellitus and colorectal cancer—obesity, Western diet, and sedentary lifestyle—and speculated about a link between these two common diseases. Accumulating evidence shows that type 2 diabetes mellitus is associated with a 40-60% increased risk of cancer of the large bowel,1 2 and specifically, proximal colonic malignancy.3 These associations are independent of body mass index and are more consistently reported than those with breast and endometrial cancers. Recent data from the European Prospective Investigation into Cancer (EPIC-Norfolk) study show that this increased risk is largely explained by changes in glycated haemoglobin (HbA_1c) concentrations.4 This implies that glycaemic control is likely to be important in determining which patients develop colorectal cancer. In contrast to type 2 diabetes mellitus, no associations have been found between colorectal cancer risk and type 1 diabetes mellitus, nor gestational diabetes.5

Recently published data from the large US Cancer …