Summary

Diabetes causes a number of complications and is known to affect the blood vessels. A team from the Mayo Clinic has carried out neuropsychological assessments that shows there is a link between long-standing diabetes, and its complications, and mild cognitive impairment, which is a precursor to dementia.

Introduction

Mild cognitive impairment (MCI) is a transition stage between normal cognitive aging and dementia. It is important to pinpoint those with MCI in case they can benefit from interventions that will slow down progression to dementia. Previous studies have identified diabetes as a risk factor in MCI and dementia. Poor blood glucose control can affect the brain through impaired blood vessel functioning and loss of neurons. But some studies have failed to demonstrate a link between diabetes and MCI, so it was important to try to clarify the association.

What was done

A team at the Mayo Clinic had been assessing the prevalence of MCI among the residents of Olmsted Country, Minnesota, and the current study is part of that. They compared 329 subjects known to have MCI with 1640 subjects free of MCI. They were all in the 70 to 89 age group. All subjects had neurologic and neuropsychological exams to diagnose normal cognition, MCI or dementia. History of diabetes, and its complications, was also recorded and blood glucose measured.

What was found

The overall frequency of diabetes was similar among those with MCI and those without. However, those whose diabetes had been diagnosed before age 65 were more likely to develop MCI, as were those who had had diabetes for more than 10 years, or were on insulin. Also, the presence of complications, like diabetic retinopathy, increased the risk of MCI.

What this study means

Severe, long-standing, diabetes is linked to high blood glucose, say the researchers. This increases the likelihood of damaging brain blood vessels which may set the scene for MCI. The fact that those with diabetic retinopathy - where blood vessels in the retina are damaged - have double the risk of MCI seems to support this view. Therefore, avoiding diabetes may help protect the long-term health of the brain. For those who already have the condition, control and management are key to reducing the risk of MCI and dementia.