Now another study suggests "education" (brain exercise) does not alter the fundamental disease process:
Bloomberg.com: U.K.The "educated" experience the same dementing process as everyone else, but they have further to fall before they meet the diagnostic criteria for dementia. Genes and brain injuries can speed or slow the fundamental dementing process. I strongly suspect the "education" marker is spurious and that IQ is really the primary protective effect, and IQ is probably almost entirely determined by genes and intrauterine environment .
... The new study shows that the brains of more educated people can tolerate changes for longer periods of time, meaning signs of decreased mental agility typical of Alzheimer's disease appear later. When those signs do appear, the disease progresses faster than it does in less educated patients.
``The amount of nerve connections and information hubs are likely to be more numerous and more efficient in people who are highly educated,'' said lead author Nikolaos Scarmeas in his study. ``The subsequent impact is likely to be greater than it would be in less educated brains, because of the higher levels of accumulated damage.'
So you can mostly relax. There's nothing you can do to slow the onset of Alzheimer's except try to avoid head injuries. Wear a helmet. Don't box or play football.
If there's any hope for folks with unlucky genes, it will come from drugs.
 Sure, lots of very good and smart people claim otherwise. I've read their stuff and my personal non-expert opinion is that it's wishful thinking. Nowadays most of the people who make serious claims about environmental impacts on IQ are thinking of the intrauterine environment.