From what I’ve read it should be an essential addition to meds. VitD switches on genes for key anti-oxidant pathways. And as we know oxidative stess kills nerve cells, especaiily those that die off to cause PD. So D3 is neuroprotective. And should allow our remaining compromised neurones to function better.
I now take D3 6000 IU pd, and shall continue to do so indefinitely whatever meds for PD I need to take in future. USA Inst of Medicine recommends 2000 to 4000 IU pd, far more than UK bodies.
My specialist a geriatrician had not heard of VitD and PD…you might be luckier but the scince is well ahead of the clinics.
Peter