Having diabetes is unhealthy enough. Now scientists have found
a link between diabetes and cancer.
By Lisa James
Diabetes is like a thief in the night, often robbing people of their health before they even know they’re ill. (The American Diabetes Association says that of the nearly 19 million people with diabetes in the US, 7 million are undiagnosed.) Marked by the body’s inability to properly control glucose, or blood sugar, diabetes leaves its victims at risk for heart disease as well as losing limbs, eyesight and kidney function.
What’s worse, nearly two decades’ worth of research has provided evidence that people with diabetes run a higher risk of developing cancer as well. In the largest study of its kind, researchers examined the records of more than 125,000 people in Sweden who had been hospitalized for complications of type 2 diabetes, the most common form; risk increases were found for 24 types of cancer (The Oncologist 6/10).
The National Cancer Institute reports that the cancer rate has been dropping in terms of both new cases and deaths. But this could change, given the relentless upward rise in the diabetes rate—to as much as a third of the adult population by 2050, according to the Centers for Disease Control.
“The biggest concern is that the obesity and diabetes epidemic may increase the rate of cancer in the next 20 to 30 years, especially aggressive cancers,” says Emily Gallagher, MD, of the Division of Endocrinology, Diabetes and Bone Disease, Mount Sinai School of Medicine, New York City.
The news is not all grim, however. Recognition of the problem has led to collaboration among major research organizations, including the American Diabetes Association and the American Cancer Society, in an effort to better understand how the two diseases are related. And for people who have blood-sugar problems, making wise lifestyle choices now can help forestall trouble later.
Scientists first noticed a link between diabetes and cancer in the early 1990s. Studies show that risk increases the most for cancers of the pancreas and liver. In addition, having diabetes doubles the risk for cancers of the esophagus, kidney, nervous system, small intestine and thyroid.
Besides increasing risk, diabetes appears to make cancer more difficult to control once it develops.
“If you have diabetes and you get breast cancer, you are more likely to die from any cause than a breast cancer patient without diabetes,” says Kimberly Peairs, MD, assistant professor of medicine at Johns Hopkins School of Medicine in Baltimore, who led a study that reached this conclusion (Journal of Clinical Oncology 1/11). “If you better control diabetes, are cancer outcomes better? That’s an area to be studied.”
Women with diabetes appear to be especially at risk for cancer. The authors of one research report found having type 2 diabetes to double the risk of female malignancies and cited hormonal changes as a possible cause (Cancer Causes & Control 6/10). This could explain why scientists have found that prostate cancer rates actually go down in men with diabetes.
Now that researchers have established the link between diabetes and cancer, they’re trying to discover why they are related. One factor may be insulin resistance, in which the body does not respond properly when insulin attempts to move glucose out of the bloodstream and into cells.
Insulin resistance, which can develop 15 to 20 years before glucose rises to diabetic levels, forces the pancreas to create more insulin in order to keep blood sugar under control. “Diabetes patients have more insulin in their blood and insulin itself may stimulate cancer cell growth. They have higher glucose levels, which may promote growth of tumors,” says Peairs.
Higher insulin levels mean higher levels of insulin-like growth factors (IGFs), proteins that help regulate cell growth. Researchers have found correlations between higher levels of certain IGFs and increased cancer risk (Endocrine Practice 9-10/10). IGFs can also promote development of new blood vessels, a process called angiogenesis that tumors use to keep themselves alive.
Insulin resistance has been linked to low-level inflammation. “We think that chronic inflammation increases insulin resistance,” explains Gallagher. “It can also cause damage to DNA, which can cause cells to have to repair themselves more frequently. If they don’t repair themselves properly, DNA mutations can turn the cell into a cancer cell.”
Colorectal cancer provides a telling example; although diabetes does increase the risk, colorectal cancer rates are going down. “We think it’s because of the use of anti-inflammatories such as an aspirin a day to prevent heart attacks,” says Lisa Richardson, MD, associate director for science, CDC Division of Cancer Prevention and Control in Atlanta. A study she coauthored suggested screening cancer patients for diabetes and a precursor called glucose intolerance (Nature Clinical Practice Oncology 1/05).
Obesity is a key—and controllable—factor that fuels both diabetes and cancer. “Almost everyone with type 2 diabetes is overweight. That’s why the 2050 projection is a concern, because we are becoming more and more overweight as a nation,” says Richardson.
Losing weight is the first line of diabetes defense. “If you lose even 5% to 10% of your body weight that makes a huge difference,” says Richardson.
What makes the idea of weight loss less daunting is that you don’t have start with drastic changes in lifestyle. “If you can learn to not ‘clean your plate’ as your mother taught you, you would go a long way towards decreasing the excess calories you may eat every day,” says Ann Peters, MD, director of the USC Clinical Diabetes Program in Beverly Hills and author of Conquering Diabetes (Plume/Penguin).
In addition to practicing portion control, Peters advises sneaking extra exercise into your day, such as parking in the far corner of the lot, avoiding escalators and elevators, and putting a treadmill or stationary bike in front of the TV. (For more suggestions, visit www.americaonthemove.org.)
Peters does not recommend any specific diet to reduce the risk of diabetes. “Whatever approach resonates with you personally is the one you should try,” she says, adding that you should work with a trained nutritionist to find the diet that suits you best. Peters does believe in eating small, frequent meals so as not to become too hungry. She also suggests planning and shopping for meals once a week to help you avoid temptation at the supermarket.
Some foods have shown anti-diabetes potential. Any carbohydrates you eat should be in whole form; refined carbs can cause glucose and insulin levels to surge. One study found that spinach and other leafy vegetables reduced type 2 diabetes risk by about 15% (BMJ 8/10).
Specific nutrients have also shown an ability to fight diabetes. Insulin depends on the mineral magnesium to function properly; in one study, supplements improved insulin sensitivity and lowered glucose levels (Diabetes, Obesity & Metabolism 3/11). A study of nearly 40,000 people found that diabetes risk dropped with increased vitamin K intake (Diabetes Care 8/10). And researchers in another study found that fish oil may activate genes that help regulate glucose levels (Journal of Nutritional Biochemistry 2/11). Other nutrients and herbs have been found to help control blood sugar levels.
Easing Diabetic Neuropathy
Excess blood sugar can lead to nerve damage, a condition known as diabetic neuropathy. Generally occurring between 10 and 20 years after a diabetes diagnosis, neuropathy can cause numbness, tingling and pain in the feet, although other parts of the body may be affected. If neuropathy is not controlled the nerves may die; if an infection takes hold because of sluggish circulation it may not be noticed until quite advanced, sometimes to the point that amputation is required.
The best way to avoid neuropathy is to keep your blood sugar levels under control (see the glucose regulators in the box above). In addition, a number of supplements may help forestall damage to nerves and blood vessels, including the small vessels that serve the extremities. For example, lipoic acid is a powerful antioxidant protects nerves helps counteract the effects of high blood sugar and cholesterol on arterial linings. (Some supplements combine ALA, the better-known form, with its nutritional partner RLA).
Homocysteine, a byproduct of amino acid metabolism that can also damage blood vessels, may rise to unhealthy levels if there is a deficiency in folic acid and vitamins B6 and B12. Vitamin C may inhibit the formation of toxins within cells. Hawthorn, an herb long used to in heart patients, has been shown to be helpful in fighting small-vessel abnormalities, as has bilberry. And the flavonoid quercetin promotes insulin secretion and inhibits glycation, in which excess glucose creates damaged proteins.