A new study shows that people with type 2 diabetes who are diagnosed with cancer ignore their diabetes in favor of cancer treatment. However, uncontrolled high blood sugar weakens their immune systems and is more likely to kill them than cancer.

The study, published in the journal Population Health Management, also showed that diabetics who received education about diabetes management after they were diagnosed with cancer were more likely to keep their blood sugar under control. They had fewer admissions to hospitals and emergency rooms, and their health care costs were also lower.

“People with diabetes hear cancer and they think that it is a death sentence, so who cares about diabetes at this point?” said Dr. June McKoy, a co-author of the study and the director of geriatric oncology at the Robert H. Lurie Comprehensive Cancer Center of Northwestern University. “But if they’re not careful, it’s the diabetes that will take them out of this world, not the cancer. That’s why this education is so critical when cancer comes on board. Patients must take care of both illnesses.”

Type 2 diabetes weakens patient’s immune system, putting them at higher risk for cancer and lowering their body’s ability to fight off cancer. For those with the disease, uncontrolled high blood sugar can cause kidney damage and blindness, or lead to foot amputation if blood vessels are damaged.

“If you are not taking good care of your diabetes, your cancer suffers, too,” said McKoy.

The study looked at five years worth of health records for 166,000 commercial insurance patients and 56,000 Medicare Advantage patients. Researchers found that 65.2% of patients who were educated about diabetes had their hemoglobin tested with a doctor at least twice over a period of three years. Among those who did not receive the education, only 48% had their hemoglobin tested over three years. The group of patients who received education had 416 emergency room visits over three years, while those who did not had 463 visits.

“If you don’t have the power of education, you are flailing in the wind,” said McKoy. “You have to get this information and physicians really need to be information brokers for our patients. Having diabetes and then getting cancer can be overwhelming.”