Breast cancer survivors over the age of 55 are at greater risk for developing diabetes than women who have never had breast cancer, a new Canadian study has found.

While the research found an increased risk for diabetes among all breast cancer patients, it detected a particular link between diabetes risk and whether a woman has undergone chemotherapy.

The study, conducted by researchers at the Institute for Clinical Evaluative Sciences and the Women’s College Research Institute in Toronto, is published in Diabetologia, the journal of the European Association for the Study of Diabetes.

For their study, the researchers looked at diabetes incidence rates among Ontario breast cancer patients aged 55 and older. They included data from 1996 to 2008, and compared it to women of the same age who had never been diagnosed with breast cancer.

The researchers found:

  • The breast cancer survivors had a 7-per-cent increase in risk for diabetes two years after diagnosis compared to women who had never had breast cancer, and a 24-per-cent increase in risk 10 years after diagnosis.
  • Breast cancer patients who had undergone chemotherapy were actually at highest risk two years after diagnosis, with a 24-per-cent increase in risk for diabetes compared to the women without breast cancer. After 10 years, that figure dropped to 8 per cent.

Lead study author Dr. Lorraine Lipscombe said the findings suggest chemotherapy may “bring out diabetes earlier” in women who are susceptible for the disease.

“Increased weight gain has been noted in the setting for adjuvant chemotherapy for breast cancer, which may be a factor in the increased risk of diabetes in women receiving treatment,” Lipscombe said in a statement.

“Estrogen suppression as a result of chemotherapy may also promote diabetes, however this may have been less of a factor in this study where most women were already post-menopausal.”

The research follows previous studies that have detected a link between diabetes and cancer. For example, recent research has suggested that women with diabetes have a 20-per-cent increase in risk of developing post-menopausal breast cancer, and have as much as a 50 per cent greater risk of death from the disease.

In this most recent study, the researchers say there are many factors that could account for an increased risk of diabetes among breast cancer survivors in addition to the effects of chemotherapy or hormone suppression, including common risk factors such as obesity and sedentary lifestyle.

“As breast cancer survival continues to improve, the long-term health consequences for this population are becoming increasingly important to understand,” they write.

The researchers say their findings suggest that greater diabetes screening and prevention strategies among breast cancer survivors “may be warranted.”