One thing people don't really seem to realize is that Alzheimer's disease is relatively new.
Alzheimer’s wasn’t even clinically defined until 1906. Disease that were more common (like smallbox, for instance) were described in excruciating detail by historians. Before 1906 there was something known as "senile dementia", which was estimated at less than 5% of those over 85.
Around between 1970 and 2000, prevalence rose to 25% to 35% of those over 85 years old.
The projections are that within 25 years, unless there's significant breakthroughs, about half of people over 85 will have Alzheimers. But with the way the incidence of this condition is growing, I would say the above estimate is optimistic.
How do you avoid this sad, debilitating, very expensive disorder?
Eat less sugar and carbs. That's it. Go on a low-carb, keto, or carnivore diet.
Sugar and carbs are VERY strongly implicated in Alzheimer's (and of course many other diseases like heart disease, diabetes, etc).
Here's a good article:
Atlantic Magazine: The Startling Link Between Sugar and Alzheimer's
https://archive.vn/U33Qv
https://www.theatlantic.cotm/health/archive/2018/01/the-startling-link-between-sugar-and-alzheimers/551528/