This is experts' opinion:

It has been scientifically proven that physical exercise and mental stimulation such as learning new things is the best way to prevent Alzheimer's, as combination of both can stimulate neuronal growth. Even for people with bad genes that make them predisposed to Alzheimer's, this is still the best way to slow down the progress. From that perspective, old Chinese sayings such as 生命在于运动，生于忧患死于安乐 是有道理的。