Individuals with mild cognitive impairment appear more likely to have earlier onset, longer duration and greater severity of diabetes, according to a report in the August issue of Archives of Neurology, one of the JAMA/Archives journals.

Rosebud O. Roberts, M.B.Ch.B., M.S., and colleagues at Mayo Clinic, Rochester, Minn., studied individuals from Olmsted County, Minnesota, who were age 70 to 89 on Oct. 1, 2004. Participants received a neurological examination, neuropsychological evaluation and tests of blood glucose levels, and completed an interview with questions about diabetes history, treatment and complications. A medical records linkage system was used to confirm diabetes history.

Rates of diabetes were similar among 329 individuals with mild cognitive impairment (20.1 percent) and 1,640 participants without mild cognitive impairment (17.7 percent). However, mild cognitive impairment was associated with developing diabetes before age 65, having diabetes for 10 years or longer, being treated with insulin and having diabetes complications.

"Severe diabetes mellitus is more likely to be associated with chronic hyperglycemia, which, in turn, increases the likelihood of cerebral microvascular disease and may contribute to neuronal damage, brain atrophy and cognitive impairment," the authors write. That individuals with the eye disease diabetic retinopathy were twice as likely to have mild cognitive impairment supports the theory that diabetes-related damage to blood vessels in the brain may contribute to the development of cognitive problems.

"Our findings suggest that diabetes mellitus duration and severity, as measured by type of treatment and the presence of diabetes mellitus complications, may be important in the pathogenesis of cognitive impairment in subjects with diabetes mellitus," they conclude. "In contrast, late onset of diabetes mellitus, short duration of diabetes mellitus or well-controlled diabetes mellitus may have a lesser effect."

This study was supported by grants from the National Institutes of Health and by the Robert H. and Clarice Smith and Abigail Van Buren Alzheimer's Disease Research Program.