A three-university research team has identified the risk of dementia varying by the period of hyperglycemia and its complications, the Yongin Severance Hospital said in a news release Tuesday.

Various studies pointed out that diabetes increases the risk of dementia by producing dementia-causing substances in the body or by chronically affecting the blood supply to the brain. However, studies on the relationship between prediabetes, diabetes complications, and dementia were relatively scarce, and their relationship was unclear.

To resolve this issue, the joint research team conducted a study based on the National Health Insurance Service (NHIS) data to examine the relationship between hyperglycemia and comorbidities and the onset of dementia.

Professors Kim Woo-jung at Yongin Severance Hospital, Lee Eun-young at Seoul St. Mary's Hospital, and Han Kyung-do at Soongsil University led the study.

The team divided all examinees over 40 who participated in the general health checkup from 2009 to 2010 into four groups -- normal, prediabetes, newly onset diabetes, diabetes under treatment for less than five years, and diabetes under treatment for more than five years – and performed a Cox regression analysis.

As a result of the analysis, the team found that the degree and duration of hyperglycemia, including prediabetes, showed a significant association with increased risks of Alzheimer's disease.

Patients with comorbidities, such as ischemic heart disease, stroke, and chronic kidney disease, showed a relatively higher risk of dementia than those with simple diabetes alone.

The researchers also found that the risk of developing dementia was higher for patients with newly onset diabetes before treatment than patients who had received diabetes treatment for less than five years of onset but lower than patients receiving diabetes treatment for more than five years.

"These results suggest that if patients manage their diabetes in the early stage, they can lower the risk of developing dementia. However, eventually, if the duration of diabetes prolongs, the risk of dementia inevitably increases," Professor Kim said. "To prevent dementia, it is crucial to prevent diabetes through sufficient exercise and proper diet control."

Based on the research, the team plans to develop a customized dementia prevention method for people with diabetes or prediabetes, Kim added.