A Chinese study in Neurology (March 2006, subscription only) studied 5000 people aged over 55 for 5 years. It found that those who developed cognitive impairment were less likely to play mahjong or to read. It showed that spending a lot of time watching television was associated with a 20% increase in risk of developing cognitive impairment.
A US study in the same journal found that crosswords, board games, reading, writing, group discussion and music prevented cognitive impairment among the elderly but watching television hastened it.
I am getting to the age where these findings become relevant. I have largely abandoned television and read quite a bit. I play a bit of chess and enjoy classical music. Will I escape 'cognitive impairment'? I'd like to see studies which included the factors above, life-style and dietary choices.