As glucose levels rise, cognitive function declines in patients who have type 2 diabetes and other cardiovascular risk factors, according to a report in the current issue of Diabetes Care.

Whether lowering glucose levels can improve cognitive function will be addressed in future assessments of the current study group, lead author Dr. Tali Cukierman-Yaffe, from Tel-Aviv University, Israel, and colleagues note.

This is not the first study to link diabetes with cognitive decline and dementia, the authors explain, but the extent to which high blood sugar (hyperglycemia) impacts cognition was unclear.

The researchers addressed this topic by analyzing data from the Memory in Diabetes substudy of the Action to Control Cardiovascular Risk in Diabetes (ACCORD-MIND) trial. Included were 2,977 subjects with type 2 diabetes who had their blood sugar levels estimated using fasting glucose levels and HbA1c.

HbA1c, also known as glycosolated hemoglobin, is a blood test to determine glycemic control. Glycated hemoglobin is a substance in red blood cells formed when blood sugar attaches to hemoglobin. The test also provides a good estimate of the patient’s average blood glucose level over the past 2 to 3 months.

The participants also completed four cognitive function tests: Digit Symbol Substitution Test (DSST); Mini Mental Status Examination (MMSE); Rey Auditory Verbal Learning Test; and the Stroop Test.

As glycemic control worsened, so did the scores on all four tests. An increase of 1 percent in HbA1c levels was associated with a 1.75-point drop in the DSST score, 0.20-point decline in the MMSE, a 0.11-point decrease in the memory score, and worse results on the Stroop Test. All of these declines were statistically significant.

By contrast, fasting plasma glucose levels did not correlate with performance on any of the tests, the report shows.

“This cross-sectional analysis illustrates that chronic hyperglycemia appears to be independently associated with cognitive function in individuals with diabetes. It also raises the hypothesis that strategies to lower HbA1c levels or prevent their rise may favorably affect cognitive function,” the research team concludes.

SOURCE: Diabetes Care, February 2009.