Glucose metabolism naturally slows with age, and memory begins to decline in our 30s, says co-author Scott Small, an associate professor of neurology at Columbia University Medical Center in New York. The new study suggests a possible association between the two, because elevated blood sugar appears to damage the dentate gyrus, Small says.

The dentate gyrus's exact function is unknown. But it's one of several circuits in the hippocampus that, if disrupted, impairs memory, such as a person's ability to learn the names of new people or to remember where they parked their car.

The possible connection between its dysfunction and poor glucose regulation may explain earlier observations that exercise benefits the dentate gyrus, Small says. Until now, scientists believed that physical activity reduced the risk of age-related memory loss by allowing glucose to be absorbed more quickly into muscle cells, but were not sure why.

this explains a lot.. wait what was is just saying?