Older men and women who have blood sugar levels at the high end of normal appear to have shrinkage of the brain in areas critical for memory, according to a new report. The findings give new weight to concerns that poor blood sugar control – typically associated with diabetes – takes a toll on the brain.
The new findings are worrisome because people in the study had blood sugar levels that were not considered high enough to put them at risk for diabetes. All were considered healthy, and none were overweight or obese.
Doctors typically test for blood sugar levels by giving a fasting blood glucose test, in which people do not eat the night before getting blood withdrawn. The blood is then measured for glucose, the form of sugar that travels through the blood and provides energy to tissues and organs, including the brain. Blood sugar levels are controlled by insulin, a hormone made by the pancreas, and high levels of blood sugar are a sign of diabetes.
With diabetes, the body either does not make enough insulin (Type 1 diabetes) or, far more commonly, it becomes resistant to insulin (Type 2 diabetes). Uncontrolled diabetes leads to abnormal levels of blood sugar and insulin, which can damage blood vessels throughout the body, including the brain. Increasingly, doctors are linking diabetes and poor blood sugar control to brain problems, including Alzheimer’s disease, leading some to call Alzheimer’s Type 3 diabetes, or brain, diabetes.
In the current study, published in the journal Neurology, researchers in Australia studied 249 men and women in their early 60s. Blood sugar levels were in the normal range: below 6.1 millimoles per liter, or 110 milligrams per deciliter. All appeared to be healthy, with no signs of obvious memory problems or Alzheimer’s disease.
The study participants were given brain scans at the start of the study, then again four years later. After controlling for factors like age, smoking, drinking and lifestyle, the researchers found that those with the highest blood sugar levels had shrinkage in two areas of the brain critical for memory processing – the hippocampus and the amygdala. Brain shrinkage in these regions is also commonly seen in those with Alzheimer’s disease and other forms of dementia.
"It has been generally assumed that blood glucose in the normal range is not a risk factor for brain health in non-diabetics," said Nicolas Cherbuin, a study author from Australian National University in Canberra. "If the present results are replicated in other studies, the definition of normal fasting blood glucose levels and of diabetes may need to be re-evaluated."
Dr. Cherbuin notes that more research is needed to better understand the many factors involved in regulating blood sugar levels. A diet high in sugary foods, lack of exercise and constant stress, for example, all likely play a role in chronically high levels, he said. "It is this chronic exposure to high glucose levels that is more likely to lead to poorer brain health," he said.
Source: N. Cherbuin, P. Sachdev, K.J. Anstey: “Higher Normal Fasting Plasma Glucose is Associated With Hippocampal Atrophy: the PATH study.” Neurology, Volume 79 (No. 10), September 2012. American Academy of Neurology.