It is claimed that thinking too much or solving too many puzzles may actually damage the brains of some older people. Indulging in too many activities like doing crossword puzzles, reading and listening to the radio is believed to have an adverse effect on mental decline.

The new research on this topic shows that initially they slow down the decline of thinking skills but brain work-outs actually speed up the progress of dementia once it is set in.

“Mentally stimulating activities may enhance the brain's ability to function relatively normally despite the build-up of lesions associated with dementia. However, once diagnosed with dementia, people with a mentally active life are likely to have more negative brain changes than others,” said study author Robert Wilson, of Rush University Medical Centre in Chicago.

He said that as a result of this people with more mentally active lifestyles could experience a faster rate of decline after dementia starts.

He added, “This reduces the overall amount of time a person may suffer from dementia.”