Crossword puzzles, mind games and other brain-stimulating activities may be getting too much credit when it comes to the topic of warding off dementia, researchers say. These mental exercises could actually speed dementia in old age, investigators suggest.

Mentally stimulating activities do delay the onset of dementia, according to researchers at Rush University in Chicago, but only initially. In their study, the researchers discovered that, once a diagnosis of dementia was made, people who partook in more mental activity saw many more dementia-related changes in their brains compared to those without a lot of mental activity. As a result, their mental acuity declined significantly faster.

Researchers evaluated 1,157 mentally healthy seniors over 12 years to determine the effect of mentally stimulating activity on the delay of, then progression of, dementia. Participants were asked to answer questions on how often they participated in mentally stimulating activities, gathering more points the more they participated.

According to the results, the average rate of decline per year for Alzheimer’s patients increased by 42% for each point, while the rate of cognitive decline among healthy seniors was reduced by 52% for each point. Researchers say they aren’t certain why this happens, according to the report, which appears in the Sept. 1 online edition of the journal Neurology.