[late follow up] I have some doubts over that correlation as it seems one common chronic use is Benedryl to go to sleep - so an overrepresentation of people with sleep issues. For that matter, sleep disorders (achronicity) are an early symptom of AD - which you probably knew. :-)
But why take a chance when there are alternatives...? And for anyone looking for an alternative to Benadryl for going to sleep, I'd suggest trying phosphatidyl serine. I find it effective for falling asleep at the 'wrong' time (jet lag). It works by reducing cortisol levels.