Dementia is a general term for a cluster of symptoms associated with progressive brain decline, such as memory loss. There is currently no cure for dementia but studies continue to deepen our understanding of the risk factors that contribute to it. It has long been known that diabetes is associated with a higher risk of developing dementia.
At the start of the study, 8.6 percent of the participants had type 2 diabetes and approximately one in three had prediabetes.
Prediabetes is characterised by blood sugar levels that are higher than normal, but not high enough yet to be diagnosed as type 2 diabetes.
After twelve years, a number of participants showed a decline in cognitive faculties. Almost 30 per cent had developed cognitive impairment. Of those who had preclinical dementia at the start of the study, 20 percent had developed dementia.
The researchers were able to conduct nuanced analyses of the part played by type 2 diabetes in the development of the disease and found that the important factor was how well-controlled the diabetes was, not the presence of the diabetes itself.
According to the treatment guidelines for older adults, HbA1C of over 7.5 percent is considered poorly controlled diabetes.
In the study, people with poorly controlled diabetes disease, compared to people without diabetes, were twice as likely to develop preclinical dementia and three times more likely to deteriorate from preclinical dementia to dementia disease.
The researchers also examined the risk of impaired cognitive health in participants who had type 2 diabetes and comorbid heart disease, in this case atrial fibrillation, heart failure or coronary artery disease.
Heart disease can be a complication in type 2 diabetes and an indication of more severe diabetes disease.
The participants who had type 2 diabetes and concurrent heart disease had twice the risk of developing preclinical dementia or dementia disease compared with those who had neither type 2 diabetes nor heart disease.
However, having either type 2 diabetes or heart disease was not associated with a higher risk.
“We didn’t find that type 2 diabetes per se entails a higher risk of developing cognitive impairment or of cognitive impairment worsening to full dementia,” said Abigail Dove, doctoral student at the Aging Research Center at the Department of Neurobiology, Care Sciences and Society, Karolinska Institutet.
“What matters is how well-controlled the diabetes is. Since there is currently no cure for dementia, prevention is vital, and here we have evidence that this can be done through the careful control of diabetes. Our results can also possibly explain why earlier studies have produced conflicting results, since few of them factor in how well-controlled the participants’ diabetes was.”