By Carolyn Crist

(Reuters Health) – People with type 1 diabetes who are able to maintain good blood sugar control may reduce their long-term risk of developing dementia, a U.S. study suggests.

Among more than 3,400 type 1 diabetes patients in a large healthcare system, those with average blood glucose readings near the normal range more than half of the time were 45 percent less likely to develop dementia than those whose readings were routinely higher, the study team reports in Diabetes Care.

“People with type 1 diabetes are living longer than ever before. This increase in life expectancy is accompanied by an increased risk of developing aging-related diseases such as dementia,” said lead study author Mary Lacy, a postdoctoral fellow at the University of California at San Francisco.

The Diabetes Control and Complications Trial, considered a landmark clinical trial, found that intensive diabetes therapy aimed at achieving glycemic control decreases the risk for developing complications such as stroke, heart disease, eye disease and vascular diseases, Lacy’s team notes. The researchers are now evaluating links between blood sugar control and dementia as well as other age-related diseases.

“Given the aging population of individuals with type 1 diabetes and the importance of cognitive function in type 1 diabetes self-care, understanding the role of glycemic control on dementia risk is especially important,” she told Reuters Health by email.

Using health records, the researchers followed 3,433 people over age 50 with type 1 diabetes who were members of Kaiser Permanente Northern California between 1996 and 2015. The research team analyzed the patients’ repeated measurements of HbA1c, a protein on red blood cells that indicates blood sugar levels over a period of two to three months.

HbA1c readings of 5.7 percent or less are considered healthy and normal, according to the National Institute of Diabetes and digestive and Kidney Diseases. And levels of 6.5 percent or more are diagnostic of diabetes. People with type 1 or type 2 diabetes are encouraged to try to get their blood sugar down and keep it as close to normal levels as possible.

Half of the study participants were followed for 6.5 years or more, and over time, 155 people, or 4.5 percent of the group, were diagnosed with dementia.

After adjusting for age, sex, race and ethnicity, baseline health conditions, and the frequency of blood sugar measurements, researchers found that patients for whom more than half of HbA1c readings were 9 percent (75 mmol/mol) or higher, had a 79 percent greater risk of dementia compared to those without such high readings most of the time.

Similarly, patients with more than half of their readings between 8 percent and 9 percent (or 64-74 mmol/mol) had a 65 percent higher risk of dementia.

At the other end of the spectrum, those with more than half of their blood sugar measurements between 6 percent and 8 percent (or 42-63 mmol/mol) had a 45 percent lower risk of dementia than people with higher readings more than half of the time.

Overall, those who developed dementia were older when the study started (age 65 versus 55) and were more likely to have a history of stroke. Among those who eventually developed dementia, the average age at dementia diagnosis was 65.

“It was really gratifying to see that, generally speaking, the HbA1c levels that were associated with lower risk of dementia are consistent with currently recommended . . . targets,” Lacy said.

Future studies should look at the mechanisms behind blood glucose control and dementia risk, which is likely related to structural brain abnormalities that come from chronic exposure to high or low blood sugar, the study authors write.

Recent research has also found an association between poor glycemic control and decreased cognitive functioning in older adults with type 2 diabetes. The lead author of one of these studies, published in 2015 in the Journal of Alzheimer’s Disease, who was not involved in the current study, noted that a type 2 diabetes diagnosis on its own was not linked with dementia risk in his team’s work.

“The diagnosis, per se, did not increase the risk of either all-cause dementia or Alzheimer’s disease,” said Dr. Alfredo Ramirez of the University of Bonn Institute of Human Genetics in Germany. “Type 2 diabetes mellitus diagnosis was not associated with an increased risk if HbA1c levels were below 7 percent.”

SOURCE: Diabetes Care, online September 4, 2018.