Cancer and diabetes: Often more than a chance encounter

Although most research supports a link between cancer and diabetes, finding the root of that connection has proven elusive.

Like familiar faces in a crowd, cancer and diabetes seem to bump into each other often. At first blush, the two diseases appear to be strangers, but scientists have found they have multiple connections and often are found together in the same patients. The results of a new study, conducted at the University of Toronto and published this summer in the American Cancer Society's Cancer magazine, conclude that patients with diabetes have an increased chance of being diagnosed with cancer just months later.

Although most research supports a link between cancer and diabetes, finding the root of that connection has proven elusive. The Toronto study offers no direct physiological connection between the two diseases, but it suggests the dual diagnosis may be explained by "increased health care visits and screening tests following a diagnosis of diabetes," says co-author  Dr. Iliana Lega, in an interview with medicalxpress.com.

How prevalent is diabetes?

Cancer and diabetes are two of the most damaging and prevalent diseases in the United States, and the world. According to the Centers for Disease Control and Prevention (CDC), nearly 30 million Americans—more than 9 percent of the population—have diabetes. The CDC also estimates that 86 million Americans have pre-diabetes. According to the American Cancer Society (ACS), nearly 14 million Americans have a history of cancer and 1.6 million new cases will be diagnosed each year.

The numbers alone suggest it's inevitable that some patients will develop both diseases. But research shows the connection is more than just happenstance. In 2010, the American Diabetes Association (ADA) published a report that explores the relationship between the two diseases and concluded: "Cancer and diabetes are diagnosed within the same individual more frequently than would be expected by chance."

The most direct connection between the two diseases is lifestyle. Diet, obesity, smoking and alcohol are risk factors for both cancer and Type 2 diabetes, also known as adult-onset diabetes, which accounts for more than 90 percent of all cases. People with Type 2 diabetes may have an increased risk of breast cancer, endometrial cancer, pancreatic cancer, liver cancerkidney cancer and colon cancer. "Diet and activity may have direct effects on risk of cancer and diabetes and also play a major role in the energy-balance equation that helps individuals achieve and maintain a healthy body weight," says Carolyn Lammersfeld, MBA, MS, RD, CSO, LD, Vice President of Integrative Medicine at Cancer Treatment Centers of America® (CTCA). "A plant-based diet that includes fish along with regular physical activity may help individuals achieve and maintain a healthy body weight to lower risk for both diseases."

What causes diabetes?

Diabetes occurs when the pancreas doesn't produce any or enough insulin to convert glucose into energy. The disease may also develop if the body cannot process the insulin that is produced. Diabetes has been definitively linked to heart disease, stroke, blindness, kidney damage and an increase likelihood of amputations due to circulatory damage. But the direct clinical connection between cancer and diabetes has vexed researchers for years. "Potential biologic links between the two diseases are incompletely understood," the ADA report says.

Still, many doctors and patients are faced with the reality of having to treat both diseases at the same time, which can be a difficult balancing act. Steroids used as part of chemotherapy regimens may increase glucose levels in the blood, making it difficult to control blood sugar during cancer treatment. This may lead to poorer outcomes, delayed wound healing and increased risk of infection. High blood sugar may also exacerbate cancer-related fatigue, and the appetite loss caused by some cancer treatments makes it difficult for some diabetes patients to eat well and maintain their blood-sugar levels.

"This requires communication between members of the health care team and the patient to modify goals and balance managing diabetes during treatment with medications and diet," Lammersfeld says. "During cancer treatment, eating quality food in the right quantities can be challenging when managing both diseases. If you are eating and feeling well, follow the guidelines for healthy eating. If you are struggling to eat, work with your health care team to liberalize your diet to make sure you meet your nutritional needs while also managing blood sugar."

Tips for managing diabetes and cancer

Lammersfeld offers these additional tips for those battling both diseases:

  • Eat a consistent amount of carbohydrates at meals and snacks. Examples of recommended carbohydrates include fruits, legumes, whole grains and low-fat dairy products like yogurt and kefir.
  • Do not skip meals. Work with your health care team to identify options for days when you are not eating well.
  • Participate in physical activity as tolerated.
  • If you are carrying extra weight, talk with your health care team about whether weight loss is appropriate and, if so, how you may achieve an optimal weight.