Monday, May 16, 2011

Is Diabetes One of the Major Causes of Cancer?

A study recently published in the journal Diabetes Care states that women who have diabetes are nearly twice as likely to develop cancer, and men who have diabetes are more than twice as likely to develop cancer. But can these findings that diabetes might be one of the major causes of cancer be taken at face value?
Diabetics are at risk for horrendous complications. Blindness, kidney failure, and limb amputations can and do occur when blood sugars are not well controlled for long periods of time.

Diabetics are also at higher risk for heart attacks, Alzheimer's disease, and even acne, freckles, and age spots. Now another study reports that diabetics are at higher risk for cancer.

The US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia did a telephone survey of 400,000 adults in the United States, asking them whether they had diabetes or cancer. Among men responding to the survey, 7% of men who did not have diabetes said they had had cancer, while 16% of men who did have diabetes said they had had cancer. Among women responding to the survey, 10% of women who did not have diabetes said they had had cancer, and 17% of women who did have diabetes said they had had cancer.

These findings are not unique. Dr. Fred Brancati of Johns Hopkins University has found that diabetics are 40% more likely to die of cancer than non-diabetics.

Are these reliable cancer facts?

There are possible methodological problems with the CDC study. It is possible that more diabetics are home-bound, and therefore more likely to pick up the phone when researchers called, so that relative rates of cancer are lower than the study found. It is also possible that more diabetics died earlier from their cancers, so that relative rates of cancer are higher than the study found. And the data in the CDC study are correlational. They don't prove cause and effect. But is there anything a diabetic can do that might reasonably lower the risk of cancer?

There just is not any proven relationship between "good" blood sugar control and the risk of cancer. I'm hesitant to report it, but the data actually show that "tight control" of blood sugar levels results in more tumors and higher rates of cancer deaths, although not "significantly" higher. That isn't a reason to go out and eat two pieces of coconut cream pie, however.

The medication metformin seems to lower cancer risk in diabetics, but not because of lowering blood sugars. Metformin acts on a specific tumor suppressor gene. And there are many reasons it is a preferred (and quite inexpensive) medication for type 2 diabetes.

Telling diabetics they are at risk for one more disease does not seem to do much good unless there is also information about what to do about it. Right now, the scientific evidence points to metformin. The commonsense evidence points to taking care of diabetes by keeping blood sugar levels low, but not necessarily being compulsive about it--at least because of cancer risk.


Micic D, Cvijovic G, Trajkovic V, Duntas LH, Polovina S. Metformin: its emerging role in oncology. Hormones (Athens). 2011 Jan;10(1):5-15.

Stefansdottir G, Zoungas S, Chalmers J, Kengne AP, Knol MJ, Leufkens HG, Patel A, Woodward M, Grobbee DE, De Bruin ML. Intensive glucose control and risk of cancer in patients with type 2 diabetes. Diabetologia. 2011 Apr 21. [Epub ahead of print]

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