It is mainly poorly-controlled type 2 diabetes that carries an elevated risk of cognitive impairment and dementia, not the diabetes per se, a longitudinal study by researchers at Karolinska Institutet in Sweden shows.
The study comprises more than 2,500 people over the age of 60 and is published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association.
It has long been known that type 2 diabetes is associated with a higher risk of developing dementia.
However, research findings have been contradictory for the risk of developing cognitive impairment – a preclinical or very early phase of dementia.
None of participants, who were followed by the researchers for 12 years, had a diagnosis of dementia when the study began, but over 700 had cognitive impairment.
Their levels of HbA1C, which indicates long-term levels of blood glucose, and CRP, an inflammation marker, were measured.
At the start of the study, 8.6% had type 2 diabetes, and approximately one in three had prediabetes.
After 12 years, a number of participants showed a decline in cognitive faculties.
Almost 30% had developed cognitive impairment.
Of those who had preclinical dementia at the start of the study, 20% had developed dementia.
Nuanced analyses of the part played by type 2 diabetes in the development of the dementia found that the important factor was how well-controlled the diabetes was, not the presence of the diabetes itself.
In the study, people with poorly-controlled diabetes were twice as likely to develop preclinical dementia and three times more likely to deteriorate from preclinical dementia to dementia disease, compared to those without diabetes.
The researchers also examined the risk of impaired cognitive health in participants who had type 2 diabetes and concurrent 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 both type 2 diabetes and heart disease had twice the risk of developing preclinical dementia or dementia disease, compared with those who had neither.
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,” says Abigail Dove, a doctoral student at the institute’s Aging Research Center.
“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.”
It is common in type 2 diabetes for there to be chronic inflammation in the body.
The same applies to many heart diseases and dementia.
In this study, the researchers observed that people with type 2 diabetes and elevated CRP levels had a three times higher risk of passing from preclinical dementia to dementia disease.
“It appears as if people with higher levels of CRP had faster progressing cognitive impairment,” says Dove.
“Inflammation seems to play an important part in this, but more studies are needed to better understand its role.”
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