It says the decline the brain experiences late in life is not inevitable. It can be affected by things like habitual exercise.

What is striking is that it didn't take much to reduce the risk ... If you don't exercise, you should start. It's never too late.

I think those people may have already been starting down that pathway toward Alzheimer's, and you can delay or reduce the rate of that pathway proceeding.

What we learned was that the modest amount of exercise would reduce a person's risk by about 40 percent.