A study of more than 1,100 participants aged 65 and older, none of whom had dementia when the research began, finds that people who regularly engage in mentally stimulating activities such as reading, doing puzzles, and going to museums  may stave off the onset of dementia longer than people who don’t. This has been shown in several other studies in the past.

But here’s the flip side: Those who are cognitively active also decline more rapidly when they do develop symptoms of Alzheimer’s disease, the new study in the journal Neurology found.

That’s not necessarily a bad thing, if you consider quality of life issues, researchers say.

“At the end of the day, you spend less of your lifespan in that demented state,” says Robert Wilson, neuropsychologist at Rush University Medical Center in Chicago, Illinois.

Participants in this study were followed for an average of 12 years. After six years, they received a full diagnostic evaluation for dementia. Researchers continued to track their cognitive functioning over the follow six to nine years.

“We found that highly cognitively active individuals who had no cognitive impairment at the beginning of the study had declined less at the end,” he said.

Keeping the mind active can help change the function and structure of the brain in such a way that when Alzheimer’s-related damage develops, the brain can better adapt to those changes, Wilson said. But exactly how that works, scientists aren’t sure.

Activities that counted toward being “cognitively active” included going to a museum, watching television, listening to radio, reading newspapers, reading magazines, reading books, and playing games. The researchers did not ask participants about whether they continued to be cognitively active after the initial assessment at the start of the study, Wilson said.

This is the first study to show a more rapid cognitive decline among people who engage in mentally stimulating activities such as reading, Wilson said.

It is also, however, an observational study and not a controlled experiment. That means researchers are drawing conclusions based on associations, but did not prove that cognitive activity caused any change at all.

The National Institutes of Health delivered the grim news in April that evidence on preventing the onset of Alzheimer’s disease continues to be fuzzy, and that there is no lifestyle modification a person can make that is proved to help.

Still, a better understanding of dementia is leading to more effective therapies. And Wilson is hopeful.

“This kind of research suggests that a cognitively active lifestyle can affect the course of the disease and how much of your lifespan it eats up,” he said.

Wilson recommends picking a mentally engaging, challenging activity that you enjoy, and doing it on a regular basis, he said. For example, reading every day or every other day could be a good hobby in this regard, he said.