Having too much excess sugar in the bloodstream is never a good thing, and can lead to medical complications such as kidney failure, cardiovascular disease, and eye problems. But could high blood sugar also cause cancer? A Swedish research team addressed this question by tracking over 500,000 patients for 10-25 yeas, and published their results in the December issue of PLoS Medicine.

Similar to the findings of a study conducted in Korea in 2005, the European research team discovered that having elevated blood glucose levels increased the risk of developing certain types cancer later in life, such as pancreatic tumors in women and liver tumors in men. Not only had more cases of cancer occurred when people had high blood sugar, but the chance of survival also plummeted, especially when the person had cervical, espohageal, or colorectal cancers.

The authors present two theories on why elevated blood glucose levels could cause cancer: 1.) high sugar diets may cause an overproduction of insulin or insulin-like growth factor 1 (IGF-1), both of which promote rapid growth of new cells, the catalyzing step to tumor formation. 2.) More glucose in the blood stream could simply be adding fuel to the fire, feeding rogue tumor cells that need lots of energy to run.

Because the studies lacked certain controls, we can’t say for sure whether elevated blood glucose levels cause certain tumors to form. For example, the people with high blood glucose levels may have been sedentary, and so the lack of exercise may be what’s actually increasing the chances of developing cancer. Regardless, this study gives yet another example of unhealthy lifestyles contributing to comorbidity, a topic discussed at length by Thomas in The Decision Tree book.