I might be in a higher risk group then: I can drink at most 1 coffee per morning (I love coffee but coffee doesn't love me). In addition, the only anti-allergy pill that works for me is a first generation allergy medicine (chlorpheniramine) that's strongly associated with increased chance of dementia. I could stop taking chlorpheniramine, but then my nose would keep me up at night, and poor sleep is also associated with increased chance of dementia.

So I am hoping there are confounding factors in all these studies, such that it's not coffee per se that helps with dementia but rather something along the lines of "the type of person who desires coffee is less likely to develop dementia".