Does having type 2 diabetes increase your risk of certain cancers?
Type 2 diabetes increases the risk of at least six cancer types, most likely primarily through chronically elevated insulin levels. A healthy lifestyle helps limit that risk.
Yes, type 2 diabetes increases the risk of quite a number of cancer types. For six types, the association has been robustly demonstrated in observational research: colorectal cancer, liver cancer, gallbladder cancer, breast cancer, uterine cancer, and pancreatic cancer. In addition, people with type 2 diabetes develop cancer at a younger age more often than people without diabetes. Cancer is now the leading cause of death in people with type 2 diabetes.
What causes this higher risk? Clues from genetic research point not so much to high blood sugar itself, but to the chronically elevated insulin levels that are common in type 2 diabetes. Insulin acts as a growth-promoting hormone: higher levels are associated with an increased risk of uterine, pancreatic, kidney, breast, lung, and cervical cancer. High blood sugar on its own appears to play hardly any role, with the exception of one specific subtype of lung cancer.
Obesity plays a key role. It is both the primary cause of type 2 diabetes and an independent risk factor for cancer. Insulin resistance, which is almost always present with excess weight, is likely the connecting mechanism.
Do you have type 2 diabetes and do you also smoke, drink alcohol regularly, exercise little, or follow an unhealthy diet? If so, the risks compound. Each of those factors further increases the risk of cancer, on top of the risk that type 2 diabetes already carries. This makes good lifestyle management especially worthwhile: not only for your blood sugar, but also as protection against cancer.
Based on multiple large observational studies and Mendelian randomisation analyses (PMID 33737302, 34521128, 32422026). Mendelian randomisation uses genetic variants to distinguish causality from mere chance or reverse causality, but is not a randomised trial.