I have over the years made a list of substances or events which make PD symptoms worse, and those whichreduce symptoms.
Typical on the "worsen" list are
Stress
Ageing
Pesticides etc
Typical of the improve list are
Curcumin
Alpha lipoic acid,
CDP Choline
GDNF
antihypertension drugs
So far, everything on the worsen list increases BBB permeability.
Everything on the improve list decreases BBB permeability.
I am still adding to each list, and recently caffeine is shown to decrease the incidence of PD.
http://www.medicine.ox.ac.uk/bandoli...d78/b78-6.html

We can add caffeine to the "improve" list since, of course, it reduces the BBB permeability. See
http://content.karger.com/ProdukteDB...ame=136581.pdf

In another post, aluminium, implicated in causing AD, increases BBB permeability, so can be added to the worsen list.

So not a [U][single exception/U] has been found.
Can this be a coincidence??? Surely not, but it is an area much neglected by research.
Ron