Your Brain on Sugar

It has long been known that memory declines with age, and that people who are active – people who exercise more – have less cognitive decline.

Now we have a clearer picture of why. It's about the sugar.

A 2008 Columbia University study showed that rising blood sugar levels, a common occurrence with aging, affect a part of the brain critical to making new memories. [1,2],

views of the hippocampus

Researchers looked at measures that typically change during aging: blood sugar and insulin levels rise, cholesterol levels rise, and obesity settles in. Researchers looked specifically at the impact of those factors on the hippocampus, a seahorse-shaped section of the brain that is critical for memory and learning. Researchers found that of all these factors, a rise in the blood glucose levels was the only one closely tied to decreasing activity in a memory-critical part of the hippocampus called the dentate gyrus.

Using high-resolution brain imaging, researchers showed that rising blood sugar levels selectively target the dentate gyrus. They mapped brain regions in 240 elderly subjects. They found a correlation between elevated blood glucose levels and reduced cerebral blood volume, or blood flow, in the dentate gyrus. Reduced blood flow is an indication of reduced metabolic activity and function in that region of the brain.

Researchers found the same association in aging rhesus monkeys and in mice.

"The paper identifies an etiology [cause] for normal age-related memory decline," said senior study author Dr. Scott Small, an associate professor of neurology at the Taub Institute for Research on Alzheimer's Disease and the Aging Brain at Columbia University Medical Center in New York City. "Elevations in blood glucose levels differentially target the dentate gyrus part of the hippocampus implicated in aging and, as we age, we develop a slight but gradually worsening difficulty in handling blood sugar levels."

Exercise helps to lower blood sugar levels, which is why older people who are more active, have less cognitive difficulties. With exercise, the muscles use up glucose in the bloodstream.

It's not enough to deliver blood sugar to the brain efficiently. The sugar must get into the cells where it can be used. If you have become insulin resistant, your brain cells may not be efficient at taking up the glucose that's delivered. About 1 in 3 Americans have at insulin resistance,[3] which if it gets bad enough can lead to type II diabetes.

The findings suggest that maintaining blood sugar levels, even in the absence of diabetes, helps maintain aspects of cognitive health.

[1] Small, S.A., Annals of Neurology, December 2008, 64, 698-706

[2] http://www.cumc.columbia.edu/news/press_releases/081230_Aging.html

[3] American Association of Clinical Endocrinologists factsheet, accessed January 2009 at http://www.aace.com/meetings/consensus/irscc/irsfs.php

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