A temporary rise in blood glucose levels in people with both types of diabetes can interfere with their ability to think quickly and solve problems.
The study has been published in Diabetes Care.
Researchers at the University of Virginia Health System ( UVHS ) found that people who had both type 1 and type 2 diabetes performed poorly on math and verbal tests when they became hyperglycaemic.
Symptoms of hyperglycemia include high blood glucose, high levels of sugar in the urine, frequent urination, and increased thirst.
Roughly 55 percent of the people in the study showed signs of cognitive slowing or increased errors while hyperglycemic, suggesting that the consequences of hyperglycemia vary among individuals.
However, among those whose cognitive performance deteriorated when blood glucose levels rose, the negative effects consistently appeared once levels reached or exceeded a threshold of 15 mmol/l or 270 mg/dl.
Because hypoglycemia can cause dizziness and an inability to focus, many people consume large amounts of carbohydrates to avoid this state prior to school exams and other cognitive-sensitive tasks. But this study suggests that carbohydrate-loading could be counterproductive, the researchers conclude, because hyperglycemia often occurs after overeating.
The best way to minimize any negative effects on cognitive functioning is to keep blood glucose levels tightly controlled, said lead researcher Daniel J. Cox, of the Center for Behavioral Medicine Research at UVHS. People who have diabetes should pay careful attention to the warning signs of hyperglycemia so that they can quickly take action to treat it.
Treatment for hyperglycemia can include increasing insulin or reducing food intake.
Source : American Diabetes Association, 2005