Writing in the journal Neurology, the research team investigated whether raised blood glucose and glycosylated hemoglobin (HbA1c) levels have an impact on cognitive functions including memory performance and hippocampal volume and microstructure in a group of healthy, older, non-diabetic people without dementia.
Led by Dr Agnes Flöel, of Charité University Medicine in Berlin, Germany, the team found that people with lower blood sugar levels were more likely to have better scores on the memory tests.
Even for people who don’t have diabetes or high blood sugar, those with elevated blood glucose levels are more likely to have memory problems, said the authors.
“These results suggest that even for people within the normal range of blood sugar, lowering their blood sugar levels could be a promising strategy for preventing memory problems and cognitive decline as they age,” said Flöel.
“Strategies such as lowering calorie intake and increasing physical activity should be tested,” she suggested.
The study involved 141 people with an average age of 63 who did not have diabetes or pre-diabetes, which is also called impaired glucose tolerance. People who were overweight, drank more than three-and-a-half servings of alcohol per day, and those who had memory and thinking impairment were not included in the study.
The participants’ memory skills were tested, along with their blood glucose, or sugar, levels. Participants also had brain scans to measure the size of the hippocampus area of the brain, which plays an important role in memory.
On a test where participants needed to recall a list of 15 words 30 minutes after hearing them, recalling fewer words was associated with higher blood sugar levels, Flöel and her team reported.
For example, an increase of around seven mmol/mol of HbA1c (a long-term marker of glucose control) was associated with recalling two fewer words.
People with higher blood sugar levels also had smaller volumes in the hippocampus, the team found.
"Our results indicate that even in the absence of manifest type 2 diabetes mellitus or impaired glucose tolerance, chronically higher blood glucose levels exert a negative influence on cognition, possibly mediated by structural changes in learning-relevant brain areas," said the authors.
"Therefore, strategies aimed at lowering glucose levels even in the normal range may beneficially influence cognition in the older population," they concluded.
Published online ahead of print, doi: 10.1212/01.wnl.0000435561.00234.ee
"Higher glucose levels associated with lower memory and reduced hippocampal microstructure"
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