(Reuters Health) - People who get diagnosed with cancer may be more likely to develop diabetes, a Korean study suggests.

The study included 524,089 men and women, ages 20 to 70, who didn’t have cancer or diabetes at the start. By the time half the participants had been in the study for at least seven years, 15,130 people had developed cancer and 26,610 had developed diabetes.

Cancer patients were 35 percent more likely to develop diabetes than people without malignancies, the study found. The excess diabetes associated with tumors persisted even after accounting for other diabetes risk factors like obesity, smoking and drinking.

“The reasons why patients with cancer may be at increased risk of diabetes are unclear,” said senior study author Juhee Cho of Sungkyunkwan University in Seoul, South Korea.

In some cases, the cancer itself or treatments used to eradicate tumors might cause diabetes, Cho said by email.

Also, Cho said, “cancer is a highly stressful experience, associated with multiple high-stress episodes such as infections, bleeding episodes, and surgery, that may also increase the risk of diabetes.”

Worldwide, about one in 10 adults have diabetes.

Most have type 2 diabetes, which is associated with obesity and aging and happens when the pancreas can’t properly use or make enough of the hormone insulin to convert blood sugar into energy. Left untreated, diabetes can lead to nerve damage, amputations, blindness, heart disease and strokes.

In the current study, the risk of diabetes varied by cancer type.

With pancreatic cancer, the increased risk of diabetes was more than five-fold, while it was roughly doubled for liver and kidney malignancies.

Gallbladder and lung tumors were associated with at least a 70 percent greater risk of diabetes. Breast, thyroid and stomach malignancies were also tied to an increased risk of diabetes.

Time also played a role, with a 47 percent greater risk of diabetes in the first year or two after a cancer diagnosis. Six to ten years after the cancer diagnosis, the increased diabetes risk was 19 percent.

The study wasn’t a controlled experiment designed to prove whether or how cancer itself or tumor treatments might directly cause diabetes. It’s also possible that some people in the study had undiagnosed diabetes before they developed cancer, researchers note in JAMA Oncology.

“A significant number of people are living with diabetes, but do not know about it as they have no symptoms,” said Tahseen Chowdhury, a researcher at Royal London Hospital in the U.K. who wasn’t involved in the study.

Even so, the findings add to a growing body of evidence linking cancer to diabetes, Chowdhury said by email.

“Cancer therapies such as steroids, and many chemotherapy and radiotherapy regimes can increase glucose (or blood sugar) levels,” Chowdhury said. “This may in part explain the link.”

“A further important factor might be that many of these patients are being seen (by doctors) frequently and having lots of blood tests, which might mean their diabetes is picked up quicker than people who do not have lots of blood tests,” Chowdhury added.

SOURCE: bit.ly/2uagWsI JAMA Oncology, online June 7, 2018.