Healthy adults with chronically high HbA1c levels performed worse in cognitive tests for memory and learning ability, researchers found. Scans showed the poor performance was likely due to brain damage caused by the high sugar levels.
Low-calorie diets and exercise could help prevent people with normal and high levels of blood glucose from developing memory problems in later life, researchers said.
Studies have shown that patients with type 2 diabetes have a greater chance of developing poorer mental function and dementia in later life. But the risks to healthy, non-diabetic adults were unclear.
Researchers in Germany gave learning and memory tests to 141 healthy middle-aged adults without diabetes, and measured levels of HbA1c, fasting glucose and insulin. The tests measured delayed recall, learning ability and memory consolidation.
The researchers also examined each participant's brain structure using imaging scans, including MRI.
They found that higher HbA1c and fasting glucose levels were linked to poorer memory performance and smaller volume of the hippocampus. In a test to recite a list of 15 words 30 minutes after hearing them, people with higher blood sugar levels recalled two fewer words for each 7mmol/L increase in HbA1c.
Further imaging revealed that the microstructure of the hippocampus was damaged following long and short-term spikes in levels of blood glucose.
Researchers suggested the damage may be caused by glucose-related increases in inflammation and blood coagulation, causing small strokes and loss of brain volume.
Study author Agnes Floel, of Charite University Medicine in Berlin, said: 'These results suggest that even for people within the normal range of blood sugar, lowering their blood sugar could be a promising strategy for preventing memory problems and cognitive decline as they age.'