Latter-day living makes moments of Zen rare, but I've found something that never fails to put me at ease. I do it every day, including when I'm at work. Sometimes I even do it with my boss. It's nothing shameful—President Clinton did it in the Oval Office, so you know it's O.K. And studies published in JAMA and The New England Journal of Medicine announce that this feel-good activity can make you smarter, more attentive, and more likely to enjoy a fuller life well into old age.

I'm talking, of course, about crossword puzzles. Though I've engaged in everyday wordplay since I was a girl (as with golf and rum, my grandmother got me hooked), it never occurred to me that it could have cognitive benefits. Then, having seen the aforementioned studies linking puzzle people with a reduced chance of developing Alzheimer's, I couldn't help but feel smart for having stuck to a brain fitness regimen all these years, even if unwittingly.

But there's a catch: Instead of wholly supporting this "neurobic" routine, scientists admit a sort of chicken-and-egg conundrum. Do crossword puzzles keep minds healthy, or are healthy minds more likely to do puzzles? "The data just isn't there for the crossword–sudoku approach," Dr. Aaron Nelson, author of The Harvard Medical School Guide to Achieving Optimal Memory and a professor at the university, told me. "The brain is a complex organ, and it's not going to benefit from some single, repetitive mental activity, as if you were doing push-ups."

If puzzles alone won't do the trick, finding other ways to fortify the brain has definite age-fighting appeal. Today, an estimated 5 million Americans suffer from Alzheimer's, and that number will certainly swell as the population lives longer: The likelihood of being afflicted doubles about every five years over the age of 65. Even without illness, brains fight a losing battle. By age 20, the cerebrum's estimated 100 billion neurons—the cells of the nervous system that process thoughts—begin to die at a rate of up to 100,000 per day.