Blood sugar spikes linked to memory decline

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Spikes in blood sugar can take a toll on memory by affecting the dentate gyrus,

an area of

the brain within the hippocampus that helps form memories, a new study reports.

Researchers said the effects can be seen even when levels of blood sugar, or

glucose, are

only moderately elevated, a finding that may help explain normal age-related

cognitive

decline, since glucose regulation worsens with age.

The study, by researchers at Columbia University Medical Center and funded in

part by the

National Institute on Aging, was published in the December issue of ls of

Neurology.

" If we conclude this is underlying normal age-related cognitive decline, then it

affects all

of us, " said lead investigator Dr. Small, associate professor of neurology

at Columbia

University Medical Center. The ability to regulate glucose starts deteriorating

by the third

or fourth decade of life, he added.

Since glucose regulation is improved with physical activity, Dr. Small said, " We

have a

behavioral recommendation — physical exercise. "

In the study, researchers used high-resolution functional magnetic resonance

imaging to

map 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, an indication of reduced metabolic activity and function in that region

of the brain.

By manipulating blood sugar levels in mice and monkeys, researchers said, they

tried to

confirm a cause-and-effect relationship between the glucose spikes and the

reduced

blood volume, Dr. Small said.

Bruce S. McEwen, who heads the neuroendocrinology lab at Rockefeller University

in New

York and was not involved in the research, said the study's findings were

" compelling, "

with important implications not just for the elderly but for the growing number

of

overweight children and teens at risk of Type 2 diabetes.

" When we think about diabetes, we think about heart disease and all the

consequences for

the rest of the body, but we usually don't think about the brain, " he said.

" This is

something we've got to be really worried about. We need to think about their

ultimate

risks not only for cardiovascular disease and metabolic disorders, but also

about their

cognitive skills, and whether they will be able to keep up with the demands of

education

and a fast-paced complex society. That's the part that scares the heck out of

me. "

Previous observational studies have shown that physical activity reduces the

risk of

cognitive decline, and studies have also found that diabetes increases the risk

of

dementia. Earlier studies had also found a link between Type 2 diabetes and

dysfunction

in the dentate gyrus.

Sheri Colberg-Ochs, an associate professor of exercise science at Old Dominion

University

in Norfolk, Va., said her research has found that regular exercise, even light

physical

activity, can offset the potentially negative effects of Type 2 diabetes on

cognitive

function. It is not clear what the mechanism is, she said, but may have

something to do

with the effect of insulin.

" This new study is interesting in that it allows for a greater understanding of

which region

of the hippocampus is likely most affected by poorly controlled diabetes, " she

said.

But the elevations in blood glucose seen in the new study are more subtle and

would not

be considered a disease state, Dr. Small said.

" It's part of the normal process of aging, much like wrinkling of skin, " he

said. " It happens

to all of us inexorably, and it worsens progressively across the life span. "

Copyright 2009 The New York Times Company