Diabetes Linked to Mild Cognitive Impairment

NEW YORK, April 9 -- Diabetes increases the risk of mild cognitive impairment with memory loss, often a precursor to Alzheimer's disease, investigators here have found.

The rate of mild cognitive impairment is especially high among groups at risk for type 2 diabetes, particularly Hispanics and African Americans, said Jos Luchsinger, M.D., of Columbia, and colleagues, reported the April issue of the Archives of Neurology.

"Our results provide further support to the potentially important independent role of diabetes in the pathogenesis of Alzheimer's disease," the investigators asserted.

They suggested that diabetes might be linked to higher risk of Alzheimer's disease by contributing to cerebrovascular disease, or by direct effects on mechanisms of amyloid deposition.

Diabetes might also be a risk factor for non-amnestic forms of mild cognitive impairment, the authors noted, but they did not have a large enough study sample to confirm the findings.

They looked for evidence of an association between diabetes and mild cognitive impairment in a multiethnic cohort of Northern Manhattan residents who were part of a longitudinal study.

The investigators studied participants who had neither mild cognitive impairment nor dementia at baseline and who had at least one 18-month follow-up interval.

They identified at total of 918 participants, all of whom had had a complete neuropsychological exam at study entry. The primary study outcome measures were the association between self-reported diabetes and all-cause, amnestic, and non-amnestic mild cognitive impairment.

There were 334 incident case of mild cognitive impairment, 47.9% of them amnestic, and 52.1% non-amnestic. The authors found that after adjusting for age, gender, years of education, ethnic group, apolipoprotein E-4 allele status, hypertension, LDL levels, current smoking, heart disease, and stroke, diabetes was still related to a significantly higher risk for all-cause mild cognitive impairment. The hazard ratio for diabetics for all-cause impairment was 1.4 (95% confidence interval, 1.0-1.8, P=0.04).

Similarly, the hazard ratio for amnestic impairment among diabetics was 1.5 (95% CI, 1.0-2.2, P=0.02). But when they looked at nonamnestic impairment, they found that the effect was significant in models controlling for some of the co-variates, but became non-significant after socioeconomic variables and vascular risk factors were thrown into the mix.

Diabetes contributed an 8.8% excess risk for diabetes among the whole, and accounted for a higher risk among African Americans (8.4%) and Hispanics (11%) compared with non-Hispanic whites (4.6%). This difference reflected the higher prevalence of diabetes in minority populations in the United States, the author noted.

"Diabetes is related to a higher risk of Alzheimer's disease," the investigators wrote. "Thus, we expected that it would be related to all-cause and amnestic mild cognitive impairment, which is a predictor of Alzheimer's disease. Because diabetes is related to a higher risk of cerebrovascular disease and vascular dementia, we also expected that it would be related to a higher risk of non-amnestic mild cognitive impairment, which is more likely to be related to vascular cognitive syndromes."

They noted that because data on diabetes in their study came from self-reports, they could not determine whether patients had hyperglycemia or glucose intolerance, or whether there might have been undiagnosed cases of diabetes that might have affected their results.