It seems there may be some hope, research is linking levels of fructose in the brain to the debilitating Alzheimer’s disease -

New research proposes that Alzheimer's disease may be driven by the overactivation of fructose made in the brain. The study outlined the hypothesis that Alzheimer's is a modern disease driven by changes in dietary lifestyle that has resulted in excessive fructose metabolism in the brain (https://www.sciencedaily.com/release...0923124802.htm)

Which suggestions that it is not a natural part of ageing and is in fact completely preventable. Of course science is looking at ways to inhibit the fructose in the brain, rather than just tell people to watch what they eat!