In fact, there’s only one practice that’s been proven, without question, to preserve your memory: exercise. "Aerobic activities tend to show larger effects than non-aerobic activities," University of Pittsburgh psychologist Kirk Erickson tells Yahoo.

I read that on this article: http://shine.yahoo.com/event/vitality/the-number-one-way-to-improve-your-memory-2401728/

The only other thing to help prevent symptoms of Alzheimer's, from what I learned on the HBO documentary as well as a study by TIME Magazine, was to have large social networks as well as those who teach. It seems that those engaged with more people in their social network as well as those who participated in exercising the mind, via teaching, for instance, showed the least signs of the horrible disease.