Exercise is our best hope at the moment, in my opinion.....

In Parkinson's, Exercise That Pushes Limits Offers Benefits, Experts Say

Agreed. We're also slowly learning more about the required aerobic intensity to halt disease progression.

For example, the knowledge gained from the recent SPARX trial [1] (mentioned in the article) where participants were assigned to one of three groups: control, moderate-intensity treadmill exercise (60 to 65 percent maximum heart rate) or high-intensity treadmill exercise (80 to 85 percent maximum heart rate). After six months researchers found that the motor symptoms of only the high-intensity group had not progressed.

[1] Effect of High-Intensity Treadmill Exercise on Motor Symptoms in Patients With De Novo Parkinson Disease: A Phase 2 Randomized Clinical Trial, Margaret Schenkman et al., JAMA Neurology: 75(2) 2018.