Diabetes and cancer – is there a link?

An estimated 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. Dr Jay Narainsamy says 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.

The link between diabetes and cancer was considered as early as 1959. 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 7 per 1000 person-years and 4 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.

Common risk factors

Diabetes and cancer have common risk factors, some of which are modifiable and some not. Non-modifiable risk factors include: age, gender and ethnicity, with increased risk in older people, men and in the African American population in the United States. Modifiable risk factors include: obesity, diet, physical activity, smoking and alcohol.

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

Diets low in processed and red meats, with a high content of vegetables, fruits and whole grains aid in lowering 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. Increased physical activity has shown to reduce the risk of certain types of cancer as well as improving overall health. Smoking and alcohol are both associated with the development of cancer as well as diabetes.

Metformin and cancer

On a further positive note, the oral diabetes medication metformin – the 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. Further studies are currently underway to assess the interaction between metformin and cancer.

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

Injectable insulin and cancer

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.

The link between diabetes and cancer

There is undoubtedly a link between diabetes and the development of certain types of cancer. With this in mind, doctors must ensure 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.

Reduce your risk

While further research needs to be done on the link between diabetes and cancer, the positive message is foundational lifestyle therapies for diabetes – healthy eating, increased physical activity, weight loss, not smoking, and first line pharmacological therapy, metformin – may have the additional benefit of reducing your cancer risk.


Dr Jay Narainsamy is a specialist physician and endocrinologist.