High-normal blood sugar could adversely impact the brain

Friday, September 7, 2012. The September 4, 2012 issue of the journal Neurology® published the finding of Australian researchers of an association between high normal plasma glucose levels and a decrease in brain volume in nondiabetic men and women. Although research has established an association between type 2 diabetes and cognitive impairment, the current study suggests an adverse effect on the brain for glucose levels considered by most authorities to be within a normal range. "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," commented first author Nicolas Cherbuin, PhD, of Australian National University in Canberra. "These findings suggest that even for people who do not have diabetes, blood sugar levels could have an impact on brain health."

The study included 266 men and women between the ages of 60 and 64 enrolled in the PATH Through Life Study, which is a longitudinal study of aging. Fasting plasma glucose and other factors were measured upon enrollment, and those with glucose levels of 6.1 micromoles per liter (110 mg/dL, classified as impaired fasting hyperglycemia by the World Health Organization) or higher were excluded. Magnetic resonance imaging (MRI) scans of the brain were conducted at the beginning of the study and four years later.

Fasting plasma glucose levels ranged from 3.2 to 6.0 micromoles per liter (57.6 to 108 mg/dL) upon enrollment. Dr Cherbuin and his colleagues uncovered a significant association between a decline in volume in the brain's hippocampus and amygdala (cerebral structures affected by aging and neurodegeneration) and higher plasma glucose levels within this nondiabetic population. "Plasma glucose levels were found to be significantly associated with hippocampal and amygdalar atrophy and accounted for 6%–10% in volume change after controlling for age, sex, body mass index, hypertension, alcohol, and smoking," Dr Cherbuin and his associates write. "These findings suggest that even in the subclinical range and in the absence of diabetes, monitoring and management of plasma glucose levels could have an impact on cerebral health."

When asked if there is a specific level at which plasma glucose would begin to be considered risky, Dr Cherbuin told Life Extension: "We found that the top two highest quarters (or quartiles) had significantly more shrinkage than the lowest one which might suggest a tentative cut-off of 5.1 [micromoles per liter]. However because overall the association with hippocampal atrophy across all glucose levels was relatively uniform, more evidence was needed to point to a specific cut-off."

He concluded that "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."