Blood Sugar Levels May Affect Hippocampus, Says Study

Memory linked to blood sugar levels

Individuals with elevated blood sugar levels are potentially at risk of developing memory problems, according to a new study presented in the latest online issue of journal Neurology, which was published by the American Academy of Neurology.

The study comprised of 141 subjects, with an average age of 63. Participants had no history of diabetes or pre-diabetes, a condition which is witnessed in patients displaying a higher than normal blood glucose level, but not high enough to be classified as full-blown diabetes. In addition, the following people were deliberately excluded from the study, for the sake of objectivity:

  • Overweight people
  • Individuals suffering pre-existing cognitive impairment or memory issues
  • Individuals who consume over three-and-a-half alcoholic beverages each day

The memory skills of participants were put to the test, using the Rey Auditory Verbal Learning Test, and blood samples were subsequently obtained to determine their blood sugar, or glucose, levels. Magnetic resonance imaging (MRI) brain scans were also performed to assess the size of a particular part of the brain, called the hippocampus, in each person.

The Rey Verbal Auditory Learning Test is designed to evaluate immediate memory recall, whereby participants are presented with a list of 15 entirely unrelated words and tasked with subsequent recall of as many of these words as possible. The process is then reiterated on two further occasions, and the final score is given as the total number of words recalled from all three tests.

The Hippocampus & Memory

The hippocampus is a major part of the human limbic system, responsible for assimilating information pertaining to short-term and long-term memory, as well as spatial

Image showing the Hippocampus in the human brain
Diagram showing the Hippocampus in the human brain

navigation. Specifically, the hippocampus is involved in episodic and declarative memories (memories that are readily verbalized, such as simple facts).

Extensive damage to the hippocampus, affecting both hemispheres of the structure, leads to difficulty in forming new memories (anterograde amnesia) and old memories (retrograde amnesia). A separate study, led by Dr. Eleanor A. Maguire of the Wellcome Department of Cognitive Neurology at University College London, looked into the cognitive affects of hypoxia-induced damage on the hippocampus of a patient called Jon. Jon demonstrated severely limited episodic memory, and could remember very little in the way of past events.

The hippocampus is one of the first parts of the brain to undergo significant damage in patients suffering with Alzheimer’s disease. Chris Zarrow, of the University of Southern California,  and his colleagues, found a relationship between the decline in the number of neurons within a specific part of the hippocampus of Alzheimer’s patients. Meanwhile, similar studies have found “functional disconnection” between the hippocampus and many other regions of the brains of Alzheimer’s patients.

High Blood Sugar Levels & Poor Memory

Participants that had low blood sugar levels, typically, showed greater aptitude for recalling words during the Rey Verbal Auditory Learning Test, yielding relatively high memory scores. Meanwhile, high blood sugar levels were associated with recall of fewer words.

glucose combines with hemoglobin
glucose combines with hemoglobin to form glycated hemoglobin (HbA1c)

Blood sugar levels were measured by performing fasting HbA1c tests. HbA1c looks at glycated hemoglobin, and measures the average plasma glucose concentration. Red blood cells are comprised of an oxygen-carrying pigment called hemoglobin. Glucose “sticks” to the hemoglobin molecules to form glycated hemoglobin (a.k.a A1c/HbA1c).

The higher the concentration of glucose within the bloodstream, the more glycated hemoglobin will be present. As red blood cells live for an average of around 120 days, the HbA1c measurement can provide an average blood glucose level over this period.

The researchers found that an increase in approximately 7 mmol/mol of HbA1c “… went along with recalling 2 fewer words.” When interpreting the brain scans of test subjects, the researchers correlated elevated blood sugar levels with smaller hippocampus volumes. If a subject’s HbA1c level went from 5 percent to 5.6 percent, this led to a reduction in the total number of words recalled.

Study author Agnes Flöel, working at the Charité University Medicine in Berlin, Germany, briefly discussed the implications of the team’s latest research endeavors:

“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.”

Flöel then goes on to discuss viable strategies for reducing blood sugar levels. She articulates her desire to see further investigation into the influence of reduced calorie consumption and enhanced physical activity in the brain structure and memory recall abilities of participants.

The researchers go on to explain that the study is relatively limited in terms of the sample size employed, pointing out that it does not substantiate cause and effect. Further clinical trials are mandated to ascertain whether reductions in blood sugar levels could aid in staving off dementia.

Speaking to USA Today, Robert Ratner, chief scientific and medical officer for the American Diabetes Association, also calls for caution in interpreting the results. He points out that the study only took a small snapshot of the blood glucose levels and memories of subjects, and does not definitively link the two factors.

However, Ratner claims it would not be “surprising” to eventually find such a link, citing the well-documented relationship between elevated blood sugar levels and increased risk of dementia as an indicator. Indeed, in a comprehensive study, published in the New England Journal of Medicine, entitled glucose levels and risk of dementia, researchers substantiated these claims. Looking at glycated hemoglobin levels from over 2000 subjects, the researchers found higher glucose levels to increase a person’s likelihood of developing dementia, in diabetics and non-diabetics.

Meanwhile, Dr. Clare Walton, who works for the Alzheimer’s Society, argues the importance of this research in understanding more about dementia. Dementia is a disease that is being described as an epidemic. According to the Alzheimer’s Association, the disease currently affects 5.2 million Americans, a figure that is projected to triple by the middle of this century.

Speaking to the Daily Mail, Walton explains the novel findings of the study:

“We already know that type 2 diabetes is a risk factor for developing Alzheimer’s disease, but this new study suggests that higher blood sugar levels may also be linked to poor memory in people without diabetes.”

By: James Fenner

American Academy of Neurology Press Release

Neurology Study

American Diabetes Association

Alzheimer’s Association

New England Journal of Medicine

Brain Journal Source

Daily Mail

USA Today

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