As per article posted on the Northwest Parkinson's Foundation website one of the best way to prevent PD dementia is to increase social interaction.
For me, right now, it requires effort to go out, or "interact" (tired, medication issues, tremor, etc) and I am only in the beginning of PD journey. Once I force myself to go out I feel better afterwords but it doesn't make it easier when I have an opportunity to do it again. Also, I live in a town where there are limited resources for PD patients. When I tried to sign up with local Parkinson organization I was told that they are full but I could be placed on the waiting list. I am thankful for interactions on this forum, no waiting list here.

http://www.nwpf.org/news.aspx?item=3721