I have been told Vitamin B12 and zinc combination assist with neurological function
Vitamin B12 (cobalamin) and zinc are both essential micronutrients with distinct roles: B12 supports red blood cell formation and DNA synthesis, while zinc is crucial for immune function, enzyme activity, wound healing, and protein synthesis
Research indicates that at standard recommended daily intake levels, zinc does not significantly interfere with B12 absorption, and there are no clinically significant interactions reported between the two .
In fact, taking them together may help cover common nutritional gaps, particularly in older adults, vegetarians, and vegans.
Personally I ask my GP to do tests twice a year but sometimes dont get the response one looks for!

I'm reading about high dose Thiamine therapy - another Bvitamin. It's still in European trials and the FDA hasn't approved trials here, but it's being tried on PD patients with thiamine deficiency, with 70-85% effectiveness.

I've read a couple of articles recently saying that people with PD may be deficient in a couple of the B vitamins. B2 and B7 (biotin and riboflavin) were the ones mentioned in the most recent article I read.