DIABETES, AS WELL as obesity and prediabetes, increases the risk of many different types of cancer, including breast, colon, endometrial, kidney, and bladder cancers. This suggests that factors other than increased blood glucose play a major role in the development of cancers, further disproving the glucotoxicity paradigm as the major cause of disease.

Insulin, a hormone well known to promote growth, can drive tumor growth, and women with the highest insulin levels carry a 2.4-fold higher risk of breast cancer. Obesity may be a contributing factor, but hyperinsulinemia is associated with an increased risk of cancer, independent of weight. Lean and overweight women, when matched for insulin level, exhibit the same risk of breast cancer.

The intimate link between insulin and cancer is reinforced by the discovery of a single mutation in the PTEN oncogene that significantly increases the risk of cancer. What’s the connection? This mutation increases the insulin effect. It lowers the blood glucose and reduces the risk of diabetes, but increases the risk of obesity and cancer.

Similarly, medications that raise insulin toxicity are associated with higher rates of cancer. Insulin use increases the risk of colon cancer by approximately 20 percent per year of therapy. The UK General Practice Database revealed that insulin increased the risk of cancer by 42 percent compared with a glucose-lowering drug that did not raise insulin. And a review of the newly diagnosed diabetics in the Saskatchewan population disclosed that use of insulin raised the risk of cancer by 90 percent.

It’s simple to understand why high insulin levels should favor cancer cell growth. First, insulin is a known hormonal growth factor. Second, cancer cells are highly metabolically active and need large supplies of glucose to proliferate. Insulin increases the risk of cancer, and once cancer has been established, high blood glucose enables it to grow faster.