Neurologists have found that even people with blood sugar that is within the “normal” range can sustain blood sugar-related brain damage. According to the study, which was published this week in the journal American Academy of Neurology, people with blood sugar levels on the high end of the “normal” range could be at risk for brain shrinkage and dementia as they grow older.

“Numerous studies have shown a link between type 2 diabetes and brain shrinkage and dementia, but we haven’t known much about whether people with blood sugar on the high end of normal experience these same effects,” said Dr. Nicolas Cherbuin, author of the study and director of the neuroimaging and brain lab at Australian National University.

The study looked at 249 people of age 60 to 64 whose blood sugar was within “normal” levels as defined by the World Health Organization. Brain scans at an average interval of four years showed that those with higher blood sugar levels were more likely to have a loss of brain volume. Researchers controlled for blood pressure, smoking, alcohol, and other factors. They estimate that blood sugar on the high end of normal accounts for 6%-10% of the brain shrinkage.

“These findings suggest that even for people who do not have diabetes, blood sugar levels could have an impact on brain health,” Cherbuin said. “More research is needed, but these findings may lead us to re-evaluate the concept of normal blood sugar levels and the definition of diabetes.”