The one thing that was very persuasively suggested long ago was that the more a person starts out with, the less she will suffer as the grip of dementia and Alzheimer's tightens with age.  I'm referring to the long-term study tracking a cohort of nuns over the course of decades.  Nuns were deemed a better group to study age-related mental decline than members of the general population since implicitly, variables such as excessive alcohol consumption, tobacco use, the indulgence of illicit drugs, and a generally unhealthy diet could be controlled or minimized. 

After many years it was observed that those nuns that when young, began their adult lives with a higher level of educational achievement, a more expansive vocabulary and related to it, very good reading comprehension and reasoning ability, were able to maintain their mental acuity longer than their peers who lacked those qualities.  It appears the more you have at the beginning - generally - the more you end up with at the end.