I have been taking curcumin for 5 years now, and after 15 years of PD I am on 250mg levodopa per day, less than Iwas on 15 years ago.
It is certainly a multifunctional supplement. As Birte said, it is a powerful antioxidant, it is anti inflamatory, it chelates heavy metals and removes them from the body. It is known to improve the efficiency of the blood/brain barrier,
I originally started taking it when I read that the incidence levels in India were 14 per 100,000 population against 280 per 100,000 in USA and UK.
It was proposed this was due to the high level of curcumin in the Indian diet.
It is a very safe supplement also, having undergone 6 human trials, and up to doses of 8 grams per day.

Ron