Type 2 Diabetes Linked to Cognitive Decline in Seniors

According to new findings recently published, among older men and women, those with type 2 diabetes have lower baseline general cognition scores and experience a steeper cognitive decline subsequently.

Dr. Olivia Okereke, of Harvard Medical School, Boston, Massachusetts, and colleagues points out that, "Although already known to be associated with major clinical sequelae, such as vascular and renal diseases, diabetes mellitus has been identified in recent large-scale epidemiological studies as a significant risk factor for age-related cognitive impairment, cognitive decline, and dementia."

For their study, the researchers examined the association between diabetes status and duration and late-life cognitive impairment and decline in 5907 men enrolled in the Physicians’ Health Study and 6326 women enrolled in the Women’s Health Study. The mean ages were 74 and 72 years, respectively, at baseline.

General cognition was assessed by the Telephone Interview for Cognitive Status (TICS), and a composite global score combined all five tests in the battery. All of the participants had second assessments approximately 2 years later. Third assessments were obtained for the women an average of 4 years later.

Overall, 553 men and 405 women had diabetes. These subjects had significantly lower baseline scores for all outcomes compared to participants without diabetes. Longer duration of diabetes was associated with lower scores (p-trends < 0.001).

Significant associations were observed between diabetes status and cognitive decline in men after 2 years of follow-up, and longer duration of diabetes was associated with worse decline (p-trends < 0.01).

Similarly, there was a significantly greater 4-year cognitive decline in all outcomes among women with diabetes compared to those without diabetes. As with men, longer duration of disease in women was associated with greater cognitive decline.
The authors note that several potential biological explanations have been proposed for the association between diabetes mellitus (DM) and diminished cognitive function. "One important potential explanation could be DM’s indirect effect on cognition through clinical or subclinical vascular disease, because DM is associated with cerebral microvascular and macrovascular damage, both of which contribute to cognitive decline," Dr. Okereke and colleagues write.

However, the researchers found that adjusting for factors related to subclinical cardiovascular disease had little effect on the association between diabetes and cognitive decline. "Thus, the findings suggest that nonvascular pathways (e.g., the effect of insulin dysfunction on the brain) may be highly important in mediating observed associations between DM and cognitive decline."
J Am Geriatr Soc 2008;56:1028-1036.

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