Midlife diagnosis of type 2 diabetes: association with cognitive impairment

This study investigated the implications of age at diabetes onset on brain pathology, and its impact on cognition in patients with type 2 diabetes mellitus.

Diabetes-related damage to blood vessels leads to brain atrophy (a condition in which cells in the brain are lost, or the connections between them are damaged) which results in a decrease of the functions controlled by that area of the brain. Cognitive impairment, defined as slowness in memory and thinking and including aspects such as awareness, perception, reasoning, and judgment is likely the result of brain atrophy. Since brain atrophy occurs before cognitive impairment, this study compared the implications of age at diabetes onset on brain pathology (disease conditions), and its impact on cognition.

A total of 1,437 participants without dementia (a decline in mental ability severe enough to interfere with daily life), were included in this study. These participants were characterized as having onset of diabetes in midlife (ages 40–64 years), in late life (age 65 years or older), or never.

Compared to late life onset of diabetes, onset of diabetes in midlife was associated with more pathologic conditions affecting the brain. These were identified by ischemic (restriction of blood supply to tissue) and atrophic imaging changes. Midlife onset of diabetes was associated with an 85% higher risk of subcortical tissue death due to failure of blood supply. It was associated with a reduction in hippocampal volume (a major memory component of the brain) of 4.0% and reduction in whole brain volume of 2.9%. Late life onset of diabetes reduced hippocampal volume by 0.8% and whole brain volume by 0.9%.

Midlife onset of diabetes was independently associated with many alterations in the measures of cognitive function. Midlife onset of diabetes elevated the risks of developing mild cognitive impairment (a slight but noticeable and measurable decline in cognitive abilities), including a 44% risk of reduction in the performance of brain executive functions (mental skills coordinated by the frontal lobe of the brain e.g. planning, organizing and remembering details). Late-life onset of diabetes was associated with fewer effects on cognitive functions.

In summary, this study concluded that midlife diabetes affects late-life cognitive abilities through loss of brain volume.

Patients diagnosed after 65 years of age may have had undiagnosed or subclinical diabetes for a number of years before diagnosis.