Tests showed that people who drank flavanoid-rich cocoa beverage had ~10-15% increase in blood flow to the brain. those who drank cocoa without flavonoids had no significant increase in brain blood flow. Cocoa that retains its flavonoids is quite bitter, so they are often removed in mass produced cocoa.
Tests were reported by Norman Hollenberg of harvard Med school, et. al. studying the Kuna Indians on the San Blas Islands off Panama (these are the artisans who make "molas" for those of you who are interested in textile folk art). These people have a very low incidence of hypertension and heart attacks, stroke and vascular dementia. when they move from the islands , this protection is lost. the difference between the population who stayed and the people who left the island was their intake of cocoa. on the island, the people drank at least 2 cups /day. the mainlanders typically did not.
(Information from Science News, March 3, 2007, vol 171 p. 142--i am sure Hollenberg's report must appear somewhere, though have not accessed it)