An elderly woman smiles while joking with a nurse during her lunch at the Canevaro old people's home in Lima.Picture taken March 25, 2010. REUTERS/Enrique Castro-Mendivil

It is common belief that staying mentally active in old age keeps Alzheimer's at bay. But once a person develops dementia despite engaging in brain exercises, he is more prone to extensive brain damage, Reuters reports according to Neurology, an online journal. This does not mean that a mentally stimulating lifestyle is a bad thing.

The researchers suspect that delaying Alzheimer's onset by keeping the mind active with hobbies, reading, crossword puzzles can cost a person. Once a mentally active older adult shows signs of dementia and later diagnosed with it, may have a more advanced stage of brain damage compared with less mentally active seniors.

The current study, led by Dr. Robert S. Wilson of Rush University in Chicago, included 1,157 older adults who were dementia-free at the outset and were evaluated for cognitive decline over roughly six years.

At the study's beginning, participants engaged in a number of activities that were considered mentally stimulating -- including reading, doing crosswords or other puzzles, playing games like cards or checkers, watching TV, listening to the radio and going to museums. During the study period, 614 participants remained cognitively healthy, while 395 developed mild impairment in their thinking abilities, and 148 were diagnosed with Alzheimer's disease.

The team found that study participants who were diagnosed with Alzheimer's were those who were the most mentally active at the study's outset. They showed a quicker rate of decline over time than those who had been the least mentally engaged.

According to Wilson's team, all of this suggests that mentally stimulating activities in older age might compress the amount of time a person ultimately spends with dementia symptoms.