Being mentally active won't prevent Alzheimer's disease, but it may delay its start.

Adults who continue to actively stimulate their brains - by reading, doing puzzles, and other mentally challenging tasks - may stave off the onset of dementia longer than people who don't. But there's a catch. Those who are mentally active also decline more rapidly when they do develop symptoms of Alzheimer's disease, according to the new study in the journal Neurology. But researchers point out these findings may mean people spend less of their lives living with this mind-robbing disease.

More than 1,100 mentally healthy adults, 65 and older, were followed for an average of 12 years. They answered questions about how often they engaged in stimulating mental activities, such as reading books, magazine and newspapers, listening to the radio, watching television, playing games, doing puzzles, and even going to a museum.

The experts think keeping the mind active in these ways encourages the brain to create more pathways for thinking- a kind of mental reserve - to help it continue to function normally even though deep within the skull, the disease may be taking shape. The study author recommends picking a mentally engaging activity that you enjoy and doing this on a regular basis, either daily or several times a week.