Dr. Rosebud O. Roberts and other experts at Mayo Clinic in Rochester studied individuals from Olmsted County, Minnesota, who were age 70 to 89 on Oct. 1, 2004.
The subjects underwent a neurological examination, neuropsychological evaluation and tests of blood glucose levels.
They also completed an interview with questions about diabetes history, treatment and complications.
The researchers used a medical records linkage system to confirm diabetes history.
Reporting their observations in the Archives of Neurology, one of the JAMA/Archives journals, the researchers said that 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 (high blood glucose), 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," the authors say.
"In contrast, late onset of diabetes mellitus, short duration of diabetes mellitus or well-controlled diabetes mellitus may have a lesser effect," they add.