Use it or lose it: that's the message from researchers who have spent 21 years studying ways to halt the onset of dementia, and have published their results today in the New England Journal of Medicine.

Doctors at the Albert Einstein College of Medicine in New York's Bronx district have found that you can significantly lower the likelihood you'll suffer from Alzheimer's or other forms of dementia if your engage in activities like playing chess or a musical instrument.

And Professor Joe Verghese has been telling our Correspondent, John Shovelan, that this sort of mental activity can reduce the risk of dementia by as much as 70 per cent.

JOE VERGHESE: Well what we found was increasing levels of participation in cognitive stimulating activities such as playing chess or checkers, bridge or reading or writing was associated with a reduced risk of dementia over this follow-up period.

JOHN SHOVELAN: Now as I understand it some mental activities brought a more positive result than others. Is that right?

JOE VERGHESE: Yes, we studied six different activities and among the activities that showed a significant effect were reading, playing a musical instrument and playing board games such as chess or checkers.

Doing crossword puzzles showed a trend towards reduced risk but the association wasn't significant according to our analysis.

JOHN SHOVELAN: So what you seem to have seen is that biological deterioration can be overcome by your habits, if in fact those habits are exercising your mind, is that right?

JOE VERGHESE: Yes. It's almost similar to, you know, the physical state where if you exercise and build up muscles then you're more resistant to injury and other illnesses. It looks like if you exercise your brain then you are also resistant to the effects of dementing illnesses such as Alzheimer's.

JOHN SHOVELAN: And is there a reason why, is there something that occurs physically in the brain as a result of chess, or crosswords, or playing a musical instrument that you can point to and say yes there is an activity in the brain that would not occur if you don't exercise the brain with those activities?

JOE VERGHESE: Yes. I mean, there's probably two possible explanations, probably even more, but the two main explanations for our finding.

One is to do with something called a cognitive reserve theory, which is that by engaging in these activities you're building a buffer or a reserve in the brain by increasing the connections between the cells or promoting new cell growth, and this way, when you do get the disease, you're resistant to the effects of the disease for a few more years. Then you only manifest the disease say three or four years later.

The other possibility, like you suggested, could be that the brain is plastic and if you challenge the brain and stress the brain by these mental activities you lay down new connections and even, you know, promote growth of new cells in areas which are affected by Alzheimer's disease.