FWIW, my caffienne avoiding (she's LDS) m-i-l has AD. Just anecdotal...but I know for myself, my second cup of coffee in the morning 'clears' the cobwebs to start the day...so maybe long term that 'clearing' helps (in addition to just being delish!!!)
Another anecdote: I know an aqauintance, 67, she drank coffe heavily, bedridden for two yrs now with Alz’s, basically incapable of anything.