|
|
HONOLULU— —Diabetes mellitus has been linked to cognitive impairment in the elderly, but the association is murky at best in some studies and quite clear in others. So which studies do we believe? According to Adnan I. Qureshi, MD, the effect of diabetes mellitus may be related to adequacy of glucose control.
Dr. Qureshi, Director of the Cerebrovascular Program at the University of Medicine and Dentistry in Newark, New Jersey, and colleagues examined the link between diabetes and impaired cognition among nearly 2,600 US residents 60 and older. “People with uncontrolled diabetes had almost twice the risk of cognitive dysfunction as those who did not have diabetes,” Dr. Qureshi told Neurology Reviews.
The good news, he added, is that adequately controlled diabetes did not increase the risk of cognitive decline. “This finding raises the important issue that aggressive glucose control may benefit patients with diabetes in terms of their ability to function cognitively and perform activities of daily living,” he suggested. The study findings were presented at the 55th Annual Meeting of the American Academy of Neurology.
All participants in the study were drawn from the Third National Health and Nutrition Examination Survey conducted by the Centers for Disease Control and Prevention during a five-year period. “The work-up on these patients was pretty extensive,” Dr. Qureshi remarked. Diabetic status was determined through tests of serum glucose and hemoglobin A1C, a marker of long-term diabetes control. Based on these tests, the patients were categorized as having normal glucose tolerance (1,671 patients), impaired glucose tolerance (ie, subclinical diabetes; 311 patients), adequately controlled diabetes (351 patients), or poorly controlled diabetes (264 patients). Patients received a cumulative cognition score based on their responses to questions designed to evaluate orientation, registration, calculation, and recall. The maximum possible score was 19.
A total of 205 patients received a low cognition score (less than 9). In a multivariate logistic regression analysis adjusting for differences in race/ethnicity, age, sex, education, hypertension, hyperlipidemia, alcohol use, body mass index, and cigarette smoking, the odds ratio for such a score was 1.9 in the poorly controlled diabetes group. No other diabetic status was associated with an increased risk of cognitive impairment.
POSSIBLE CAUSES
Dr. Qureshi suggested that poorly controlled diabetes may impair cognition by compromising the microvessels of the brain and causing small strokes. “These strokes could be small enough that the classic signs of stroke are not apparent but large enough to produce ischemic damage that affects cognitive function,” he said.
Another hypothesis is that a high level of glucose may directly damage the neurons, although, Dr. Qureshi cautioned, “Currently, we have limited understanding about how chronically elevated serum glucose interferes with the function of brain cells in a way that causes cognitive impairment.”
—Timothy Begany
Suggested Reading
Haan MN, Mungas DM, Gonzalez HM, et al. Prevalence of dementia in older Latinos: the influence of type 2 diabetes mellitus, stroke and genetic factors. J Am Geriatr Soc. 2003;51:169-177.
Hewer W, Mussell M, Rist F, et al. Short-term effects of improved glycemic control on cognitive function in patients with type 2 diabetes. Gerontology. 2003;49:86-92.