A few replied to the relevant post on this site of 4 years ago, but it's probably worth repeating for those who missed it: a 40% reduction in risk of PD (for those getting the most flavonoids versus those getting the least) is big! A mystery is why this dietary strategy does not work for women.
Another very common question with this kind of finding is whether risk-reduction by a therapy implies it will help treat/cure/slow the disease once you've got it. We usually assume this is so.
michaeljfox.org/foundation/...
Original journal article on the massive, 20-year study:
ncbi.nlm.nih.gov/pmc/articl...