Elevated Sugars Linked to Brain Shrinkage

"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. " The study involved 249 people age 60 to 64 who had blood sugar in the normal range as defined by the World Health Organization. The participants had brain scans at the start of the study and again an average of four years later.

Those with higher fasting blood sugar levels were more likely to have a loss of brain volume in the areas of the hippocampus and the amygdala, areas that are involved in memory and cognitive skills, than those with lower blood sugar levels. 

Interesting note:

A fasting blood sugar level of 180mg/dl.(10.0 mmol/l) or higher was defined as diabetes and a level of 110mg/dl(6.1 mmol/l) was considered impaired, or prediabetes. 
This part is the language of an epidemiological study:

After controlling for age, high blood pressure, smoking, alcohol use and other factors, the researchers found that blood sugar on the high end of normal accounted for six to 10 percent of the brain shrinkage. 

http://www.diabetesincontrol.com/index.php?option=com_content&view=article&id=13511&catid=1&Itemid=17

These are interesting results, in that they correlate with the widely held view that high blood sugars are injurious to the nervous system.  In fact, for a while it was fashionable to cause Alzheimer's "Type III Diabetes" or "Alzheimer's of the brain."  However, as the authors noted, epidemiological studies only suggest a possible cause, and prove nothing.  Whether or not the effect is as dramatic as showing a loss of brain tissue in four years, there are many reasons to fear high blood sugar's negative impacts on your health, and zero negative side effects of eating for glycemic control.