Diabetes mellitus is a metabolic disorder in which blood sugar levels are abnormally high. This can cause ketoacidosis and hyperosmolality in the short term and in the long term predisposes to atherosclerotic disease. Ultimately, diabetes increases the risk of heart disease and stroke through hardening of the arteries of the heart and brain. There have been several studies that have shown that diabetes increases the risk of mild cognitive impairment and dementia. We have previously discussed the findings of Dr. Yutaka Kiyohara and colleagues regarding the association of diabetes with increased risk of developing dementia in a Japanese population. Researchers, lead by Dr. Kristine Yaffe, have added to the body of work that suggest that diabetes confers an increased risk of developing mild cognitive impairment and dementia. The results of the research were published online in the Archives of Neurology. In the current study, the researchers also investigated whether newly diagnosed diabetes can lead to declining cognitive function. The investigators used a prospective cohort study design with the Health, Aging, and Body Composition (Health ABC) Study at two community clinics. There were a total of 3,069 study participants with a mean age of 74.2. The study participants were evaluated with the Modified Mini-Mental State Examination (3MS) and Digit Symbol Substitution Test (DSST) at the onset of the study and at various times during the 9 years of follow up. Diabetes mellitus status was evaluated at the onset of the study and at various intervals throughout the study. Overall diabetes control was assessed by measuring hemoglobin A1c (HA1c) levels during the course of the study. The investigators found that study participants with diabetes had lower test scores for cognitive function as compared to those study participants without diabetes. Study participants who developed diabetes during the course of the investigation were found to have lower cognitive function as compared to study participants who did not develop diabetes during the course of the study. In addition, individuals with poorly controlled diabetes, as measured by HA1c levels, were found to have declining cognitive function. These results remained even after correcting for possible confounding factors. The authors of the study wrote, “In this prospective study of well-functioning older adults, persons with prevalent [diabetes] had lower baseline and greater 9-year decline in cognitive scores compared with participants who remained free of [diabetes] over the follow-up. Participants who developed [diabetes] during follow-up tended to have scores between those without [diabetes] and those with prevalent [diabetes] but scores were not statistically different from the non-[diabetes] group. Decline scores on the 3MS among those with incident [diabetes] were also similar to those with prevalent [diabetes]. In addition, participants with [diabetes] who had a higher HbA1c level performed more poorly on cognitive tests, suggesting that glucose control is related to cognitive function”. The investigators propose that diabetes and poorly controlled blood sugar levels may contribute to cognitive decline by increasing risk for renal disease, depression, stroke, hypertension, hyperlipidemia, and cardiovascular disease. Future studies should focus on the treatment of diabetes in patients with mild cognitive impairment and dementia, and determine whether better control of diabetes can prevent or slow the progression of cognitive decline in diabetics.
Kristine Yaffe et al. “Diabetes, glucose control, and 9-year cognitive decline among older adults without dementia” Arch Neurol 2012; DOI: 10.1001/archneurol.2012.1117