Scientists have found yet another reason to slim down: having a high blood sugar may contribute to the failing memory of old age.
A small study, published in the Proceedings of the National Academy of Sciences, showed that middle-aged and elderly people with high blood sugar actually had a smaller hippocampus, the brain region so crucial for recent memory.
If the findings are confirmed, simple diet and exercise could help many people protect their brains.
For every Alzheimer's patient, there are eight older people who suffer enough memory loss to significantly harm their quality of life even though they have no dementia-causing disease, says a NYU psychiatry professor who set out to uncover the causes.
Blood sugar was a natural suspect for memory loss because scientists have long known that diabetics are at higher-than-normal risk for memory problems. Diabetes harms blood vessels that supply the brain, heart and other organs.
The new study found that people's memory may be harmed long before they ever develop full-fledged diabetes -- and that it's a problem of fuel, not plumbing.
The NYU researchers studied 30 non-diabetic middle-aged and elderly people. He measured how they performed on several memory tests; how quickly they metabolized blood sugar after a meal; and, using MRI scans, the size of the hippocampus.
The slower those outwardly healthy people metabolized blood sugar, the worse their memory was -- and the smaller their hippocampus was.
Unlike most other tissues that have multiple fuel sources, the brain depends on blood sugar for almost all its energy. The longer that glucose stays in the bloodstream instead of being metabolized into body tissues, the less fuel the brain has to store memories.
The study found no specific threshold at which memory automatically worsened. Overall, though, the slower the glucose metabolism, the worse people did.
Once that metabolism reaches certain levels, it becomes a condition called "impaired glucose tolerance" or pre-diabetes. It strikes mostly in middle age, although people of any age who are overweight and sedentary are at risk. Without treatment, pre-diabetes usually turns into type 2 diabetes.
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