The NYT’s Well blog has the details. The brain’s hippocampus is a critical center for memory. Alzheimers disease is associated with a gene called apo-E4. Carriers of that gene who exercise regularly have less shrinkage of the hippocampus than non-exercisers.
To PROVE that regular exercise prevents dementia-related shrinkage of the hippocampus, you’d have to force some folks to exercise and stop others who wanted to exercise. A couple years later, scan their brains and compare the two groups. That study may never be done.
Another way to preserve your memory could be to keep your fasting blood sugars closer to the lower end of the normal range, rather than the higher end. That strategy may prevent degeneration of your hippocampus and amygdala.
The Mediterranean diet also seems to prevent or forestall dementia.
Steve Parker, M.D.
Paleo Diabetic 