Several months ago, I saw a video in which a neurologist said that there may be thirty or more types of Parkinson's, and that we might hope to see cures for one or two of them every five or ten years.
What this suggests to me is that it may be very difficult to find treatments that slow, stop, or cure the disease(s), because whatever combination of medications, supplements, or types of healthy activities (such as exercise or meditation), benefit one individual might not help another with a different type or sub-type of PD. Complicating the matter further, there may be other variables, such as the order in which various meds and supplements are taken, whether the disease (and consequently the treatment or cure for a particular individual) changes over time, whether the individual has other chronic conditions, etc..
It may be the kind of futile situation in which one finds a way out of a maze, only to realize that he's at the center of bigger maze.