In addition, people with insulin resistance--a loss of sensitivity to this key blood-sugar-regulating hormone--tended to have a relatively small hippocampus, a region in the brain associated with short-term memory.

"This (finding) might give baby boomers a motivation to get off their couches and on their treadmills," said Dr. Antonio Convit of New York University and the Nathan Kline Institute for Psychiatric Research in Orangeburg, New York.

Although insulin resistance commonly results from excess weight and lack of exercise, most people who have the condition don't know it, and may consider themselves to be perfectly healthy, Convit told Reuters Health.

So while people may not be motivated to exercise and diet to improve their appearance, Convit said he hoped that the thought that their lifestyle was affecting their memories, as well as the shape of their brains, might do the trick. Past studies have suggested that full-fledged diabetes can also put people at risk of memory problems.

In the new study, Convit and his team obtained their findings from brain scans, memory tests, and tests of insulin resistance in 30 people without diabetes who were between 53 and 89 years old. They reported their results in the early online edition of the Proceedings of the National Academy of Sciences.

In an interview, the researcher explained that when people become resistant to insulin--a condition also known as impaired glucose tolerance--they have trouble getting glucose (blood sugar) out of the blood and into the tissues that need it.

During the test of glucose tolerance, Convit and his colleagues injected people with a certain amount of glucose--roughly equivalent to two donuts' worth, Convit said--and took many blood samples.

The authors discovered that people who had more trouble clearing glucose from their blood also tended to perform less well during tests of short-term memory. Brain scans also revealed that the size of the hippocampus tended to be smaller in people with insulin resistance.

Convit explained that the brain relies on glucose for fuel, and the hippocampus is especially vulnerable to stress. People with insulin resistance are unable to bring glucose to where it needs to go, he said, and a lack of fuel might affect how well the brain--in particular, the hippocampus--develops.

Whether these memory problems are permanent or not remains unclear, he said. However, diabetics who get their condition under control often also see an improvement in their memory, Convit noted, a sign that reduced memory is also reversible in pre-diabetics.

For people who know or fear they are insulin resistant and "want to retain as much of their marbles as possible," Convit recommended that they exercise and lose any excess weight--the best methods of getting blood sugar under control, he noted.

SOURCE: Proceedings of the National Academy of Sciences 2003;10.1073/pnas.0336073100.

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