Parkinson’s dis-ease is due to accumulation of heavy metals in the brain and most likely throughout the nervous system. I developed it as a child and lived with it throughout my teenage years from the placement of 5 mercury fillings.
The human body can produce Metallothionein proteins to remove these heavy metals but a lack of Vitamin A and D will prevent the production of these proteins. Fasting also increases Metallothionein proteins when there’s sufficient Vitamin A and D. So too much insulin and not enough growth hormone most likely suppresses the production of Metallothionein proteins.
Beta-carotene neutralises heavy metals. I noticed major benefits after consuming carrots for a couple weeks.
I wouldn’t be surprised if the composition of fat intake turned out to be implicated in one way or another. Given that the brain is largely fat and cholesterol, a possible mechanism for damage might be the introduction of trans-fats and polyunsaturates from industrial seed oils that replace the fats that the body really needs. Also, as Chris Knobbe points out, anything that disrupts mitochondrial health is going to pose a problem to the body.