One thing I've always been perplexed by, and I remember when I asked questions about this years ago I was surprised by it, is how little we really knew about the brain. It was a very frustrating process. I've heard people say that mental activity certainly helps avoid the onset. Then I think of people like Ronald Reagan and Margaret Thatcher, who have had incredibly stimulating lives. You hear about physical activity, but then you hear in the NFL there are higher rates of Alzheimer's and dementia than anywhere else, and they have incredible levels of physical activity.
How certain are we that those are means to delay onset? When you see examples like that, it certainly causes confusion.