Is there a link between Bipolar Disorder and Alzheimer's?

Not sure if there is a factual answer to this question or if it’s pure speculation.

Here’s why I wonder: I’ve taken my Grandma to a few doctor’s appointments recently, and when they find out she’s taking Risperdal (for dementia/Alzheimer’s) they ask me if she has a history of Bipolar Disorder.

I looked at risperdal.com, and I found that it’s primarily used to control manic episodes. But I want to know if someone who has Bipolar Disorder is more likely to suffer from dementia or Alzheimer’s later in life.

Any responses would be greatly appreciated, factual or personal experiences. This has been preying on my mind for months.