Diabetes and Dementia

Abstract & Commentary

By Michael Lin, MD, PhD, Assistant Professor of Neurology and Neurosciences, Weill Cornell Medical College. Dr. Lin reports no financial relationships relevant to this field of study.

Synopsis: Diabetes mellitus is a risk factor for dementia, and poor glucose control is associated with worse cognitive function and greater decline.

Source: Yaffe K, et al. Diabetes, glucose control, and 9-year cognitive decline among older adults without dementia. Arch Neurol 2012;69:1170-1175.

Alzheimer's Disease (AD) and strokes (vascular dementia) are the most common causes of dementia in aging, and there is a close relationship between the two. At least half of AD cases at pathology have other significant pathology, most commonly stroke, and at least three quarters of vascular dementia cases have associated AD pathology. There is also a close relationship in their risk factors; many risk factors for stroke — including hypertension, hyperlipidemia, and diabetes — also are risk factors for AD.

This is particularly well illustrated by the recent study from Yaffe and colleagues reporting that diabetes mellitus (DM) and elevated hemoglobin A1c (HbA1c) among those with DM are associated with worse cognition at baseline and greater decline over time. A total of 3069 older adults (mean age 74.2) without dementia were followed prospectively for an average of 9 years at two community clinics in the Health, Aging, and Body Composition (Health ABC) study. DM status and HbA1c were determined at baseline and during follow-up. Cognition was assessed using the modified Mini-Mental State Exam (3MS) and digit symbol substitution test (DSST) at baseline and during follow-up.

At baseline, 23% of participants had prevalent DM, and during follow-up, 5.2% developed incident DM. Prevalent DM was associated with black race, male gender, lower education, history of hypertension or myocardial infarction (MI), and higher body mass index (BMI). After adjustment for all these associations, prevalent DM was still associated with lower baseline 3MS and DSST scores, and with greater decline in 3MS and DSST scores, compared to those without DM. Subjects with incident DM tended to have baseline scores and mean declines intermediate between subjects with prevalent DM and those without DM. Among subjects with prevalent DM, higher HbA1c levels (mid and upper tertiles) were associated with lower 3MS and DSST scores than the lowest tertile of HbA1c.

Commentary

Other studies have also reported an association between DM and increased risk of cognitive impairment with aging.1 This was a large prospective study, with a diverse sample and long follow-up, and the results reinforce the notion that maintenance of general health, with particular emphasis on control of vascular risk factors, might reduce the risk of dementia or possibly reduce the rate of cognitive decline in dementia. As an outgrowth of these epidemiological studies, a new trial of intranasal insulin for treatment of early AD has been initiated.

Reference

1. Biessels GJ, et al. Risk of dementia in diabetes mellitus: A systematic review. Lancet Neurol 2006;5:64-74.