Is there a link between diabetes and cancer?

It is estimated that up to 4.6 million people are living with diabetes in South Africa and an alarming 60 000 new cases of cancers are reported annually, according to the South African National Cancer Registry.

“It is important to delve into the link between these two prevalent conditions in the hope that this understanding may lead to better lifestyle choices and positive changes in clinical management,” says Dr Jay Narainsamy, Specialist Physician/Endocrinologist, Centre for Diabetes and Endocrinology (CDE).

A report in the New England Journal of Medicine in March 2011 looked at causes of deaths in patients with diabetes.

“The article estimated cancer-related deaths at seven per 1000 person-years and four per 1000 person-years among men and women respectively. Diabetes was associated with an increase in cancer-related deaths involving the pancreas, ovaries, liver, colorectum, breasts, lungs and bladder,” explains Dr Narainsamy.

Common risk factors

Diabetes and cancer have a number of common risk factors, some of which are modifiable and some not.

Non-modifiable risk factors include age, gender and ethnicity, with increased risk for older people, men and the African American population in the United States.

Modifiable risk factors include obesity, diet, physical activity, smoking and alcohol.

Uncontrolled diabetes may welcome tumour growth

“Obesity is linked to the development of insulin resistance and type 2 diabetes. It is thought that the high levels of insulin produced by the body to compensate for insulin resistance and obesity-associated inflammation may precipitate cancer development,” says Dr Narainsamy.

“In addition, diabetes itself (especially if not controlled) may cause vascular damage and an inflammatory state, which may create an environment for tumour development.”

Three protective steps

Eat – following a diet low in processed meats, red meats and high in vegetables, fruits and whole grains lowers the risk of developing certain cancers. A healthy diet may also lead to weight loss and reduce the risk of developing insulin resistance and diabetes.

Exercise – increased physical activity has shown to reduce the risk of certain types of cancer, as well as improving overall health.

Quit – smoking and alcohol are both associated with the development of cancer as well as diabetes.

Diabetes medication may help fend off cancer

“On a further positive note, the oral diabetes medication metformin, which is our first-line drug of choice for patients with type 2 diabetes, has been shown to inhibit abnormal cell growth and has potential anti-cancer properties,” says Dr Narainsamy.

“Further studies are currently underway to assess the interaction between metformin and cancer.”

The link between diabetes and cancer in the other classes of oral diabetes agents are, however, less conclusive.

“On the opposite spectrum, injectable insulin was thought to be associated with an increased risk of cancer development. However, this has not been conclusively proven and risk is probably better evaluated in the context of duration of diabetes, other oral diabetes agents already on board and poor glycaemic control.”

“There is undoubtedly a link between diabetes and the development of certain types of cancer. With this in mind, it is important that doctors ensure that routine screenings for at-risk patients are completed timeously. They also need to be vigilant for ‘red flag’ complaints and act promptly to investigate these problems,” says Dr Narainsamy.

“While further research still needs to be done on the links between diabetes and cancer, the positive takeaway message is that foundational lifestyle therapies for diabetes, including healthy eating, increased physical activity, weight loss and not smoking, as well as our first-line pharmacological therapy, metformin, may have the additional benefit of reducing your cancer risk,” she concludes.

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