It's from the newspapers that people I know - relatives and co-workers - have got the idea that crosswords are a prophylactic against Alzheimer's. Newspapers are of course also the place where crosswords (and now sudokus) are most readily available, so the association is presumably good for circulation.
Alan Connor, Two Girls, One on Each Knee (7): The Puzzling, Playful World of the Crossword
crosswords, fact, fiction, framing, newspapers, reporting, research