Any intellectually stimulating activity can potentially stave off brain disease but crosswords are particularly well suited to maintaining mental agility --- to complete them requires daily, sustained bursts of cognitive effort.
The activity features almost universally in checklists of how to ward off neural decline, and is even a component of an experimental "brain boot camp" developed by experts on ageing at the University of California.
Those who flexed their brains most regularly almost halved their risk of developing Alzheimer's disease.
While physical exercise did not seem to delay the onset of Alzheimer's, intellectual exercise did.
Those who did four crossword puzzles a week were less likely to develop the disease than those who managed only one.
Other protective activities included chess, draughts, card and board games, museum visits, reading, playing a musical instrument and ballroom dancing (the last two require a good working memory and a degree of co-ordination).
It is unclear, though, how regular brain workouts are able to postpone Alzheimer's; this is now the subject of ongoing research.
The absence of an obvious biological mechanism has inspired worries that the link between mental exercise and delayed Alzheimer's onset is fictitious.
This means that even among people who left education early, the ones who enjoy puzzles, play games and stay mentally active still enjoy a lower risk of Alzheimer's.
This strengthens the theory that using your brain regularly really does sharpen and protect it.