What percent of seniors over 75 years in age have alzheimer's disease?

See below: It has been noted in the literature that about 50 % of all seniors acquire dementia by age 85 (most are alzheimer's but some mixed with small strokes also). Based on a reverse approximation, likely that the risk at age 75 probably about 35%. However, be somewhat cautious, as many seniors with so-called dementia may well be experiencing anti-cholinergic rxtns from medications.

About 10 percent: The prevalence of alzheimer's disease increases two fold with every 5 years of age, reaching almost 50 percent in people older the 85.