One 2014 study found that among adults ages 50 to 69, those taking a cocoa supplement with high flavanol content for three months had better performance on tests of memory than those assigned to take a low-flavanol cocoa supplement.
By Lupus in Saxonia (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons