Recently I listened to a talk about PD at a scientific conference. The speaker has both medical qualifications and a PhD.

He made the point, backed up with a lot of technical detail in both cases, that PD is not "one disease" any more than cancer is "one disease".

He concluded that it is most unlikely that high doses of Vitamin C will be a "silver bullet" for treatment of all of the many forms of PD any more than there will ever be a "silver bullet" for treating all of the many forms of cancer.