Blood Sugar Levels Linked to Normal Cognitive Aging

A new study has found that memory loss in senior citizens is linked to increased blood glucose levels, and suggests that exercise, even in the absence of disease, may be an important strategy for preserving cognitive health.

Researchers at Columbia University Medical Center (CUMC; New York, NY, USA) used high-resolution functional Magnetic Resonance Imaging (fMRI) to map the specific areas of the hippocampus impacted by late-life diseases such diabetes and stroke. The researchers discovered that decreasing brain function in an area of the hippocampus called the dentate gyrus was a main contributor to normal decline in memory as people age. The researchers then looked at measures that typically change during aging, such as elevated blood glucose levels, body mass index (BMI), cholesterol, and insulin levels, and found that the decreasing activity in the dentate gyrus only correlated with levels of blood glucose. Additional animal studies in aging rhesus monkeys and mice confirmed the relationship between glucose and dentate gyrus activity.

Previous imaging studies at the CUMC in both humans and in mice have documented that among all hippocampal subregions, only physical exercise causes an improvement in dentate gyrus function. The study was published in the December 2008 issue of Annals of Neurology.

"Beyond the obvious conclusion that preventing late-life disease would benefit the aging hippocampus, our findings suggest that maintaining blood sugar levels, even in the absence of diabetes, could help maintain aspects of cognitive health,” said lead author Scott Small, M.D., an associate professor of neurology at CUMC. "More specifically, our findings predict that any intervention that causes a decrease in blood glucose should increase dentate gyrus function and would therefore be cognitively beneficial.”

The dentate gyrus is thought to contribute to the formation of new memories, which preferentially utilize newly formed cells, providing a potential mechanism for distinguishing multiple instances of similar events, or multiple visits to the same location. Additionally, the dentate gyrus may be important in recognizing the differences that make each place unique. Thus, damage to the dentate gyrus could play a role in the déjà vu phenomenon. The dentate gyrus is also notable for being one of a select few brain structures currently known to have high rates of neurogenesis in adult humans, with other sites including the olfactory bulb and cerebellum.

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