BOSTON -- We all forget the keys occasionally, or what we had for lunch yesterday. But when you're a senior citizen, forgetfulness can be frightening -- and perhaps a sign of dementia, for which there is no cure.

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Use It Or Lose It RESOURCES What is dementia? How do you treat dementia? Signs of dementia Alzheimer's Association New England Journal of Medicine

There's now more evidence that an active mind may significantly lower that risk.

Some seniors read, others work crossword puzzles. And some play poker twice a week for fun, and a little change.

"We play 5 and 10, and we have a kitty, and you can't bet more than a quarter," card player Florence Rose said.

But they may be substantially upping the ante when it comes to brainpower. A new aging study found certain leisure activities played regularly may stave off dementia.

In the study of 469 elderly people, those in the top third in mental activity had a 63 percent lower risk of dementia than the bottom third. Taking part in a single activity one day a week reduced the risk by 7 percent. Those who did crossword puzzles four times a week were 47 percent less likely to develop dementia than those who did not. Seniors who played musical instruments, board games or read regularly had similar risk reductions.

"The findings are significant," said Richard Jones, spokesman for Hebrew Rehabilitation Center for the Aged in Boston.

But epidemiologists are quick to point out the 21-year study published in this week's New England Journal of Medicine offers no proof, only observations. And it has limitations -- participants were predominantly white.

"However, it's hard to imagine how the results that were demonstrated in the research wouldn't apply to people belonging to other groups," Jones said.

The use-it-or-lose-it notion is not a new idea. But it is hard to prove, since early dementia without obvious symptoms may cause people to slack off their hobbies. If this is so, dementia affects hobbies -- and maybe not the reverse.

Experts say it's possible leisure activities increase connections between nerves in the brain, but they don't really know. One thing is certain: unlike drugs, they have no harmful side effects and may stack the deck in your favor.