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Rising Blood Sugar May Harm the Aging Brain

TUESDAY Dec. 30, 2008 -- Scientists have unmasked what appears to be a major mechanism contributing to normal, age-related cognitive decline.

Happily, it's a mechanism that is amenable to change: rising blood glucose levels, which means that exercise might be the antidote.

Researchers reporting in the December issue of Annals of Neurology showed that rising blood sugar levels, a normal part of aging, affect a part of the hippocampus, a part of the brain critical to learning and memory.

"This would suggest that anything to improve regulation of blood glucose would potentially be a way to ameliorate 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.

The findings may also help explain why people who exercise don't have as many cognitive problems as they age: Exercise helps stabilize blood glucose levels.

"We had previously shown that physical exercise strengthens a part of the brain involved with aging but, at the time, we didn't know why physical exercise would have this selective benefit," Small said. "Now we have a proposed mechanism. We think it's because subjects who exercised had better glucose handling."

It's well known that damage to the hippocampus is evident with Alzheimer's disease, and there has been some suggestion that this region of the brain is also affected by normal aging.

The researchers used MRI to record the functioning of the hippocampus in 240 healthy older people (average age almost 80). Sixty of the participants had type 2 diabetes, while 74 had brain "infarcts" -- some damage to brain tissue. Diabetes and infarcts were each linked with separate areas of the hippocampus, indicating that different mechanisms are at work in each disorder.

The findings were confirmed in animal tests.

"The paper identifies an etiology [cause] for normal age-related memory decline," Small explained. "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."

That difficulty coincides with the beginning of loss of cognitive function, Small added.

"In my opinion, that's an interesting hypothesis and needs to be studied -- that exercise helps improve cognitive functioning through that mechanism, but I think there are other mechanisms as well," said Bryan Freilich, a clinical neuropsychologist at Montefiore Medical Center in New York City.

Mark Mapstone, an associate professor of neurology at the University of Rochester Medical Center in New York, said: "If these findings are replicated and confirmed, I think the implications could be very important, specifically, that maintaining optimal blood sugar levels throughout aging is a feasible way to [slow or prevent] cognitive decline. It goes beyond diabetes to look at people who don't have diabetes. The implication is even if you don't have a clinical condition of diabetes, that you can still do something about cognitive aging."

More information

For more on healthy aging, visit the U.S. National Institute on Aging.

Posted: December 2008


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