... helps keep the crazies at bay:

Regular exercise may reduce the risk of dementia and Alzheimer’s disease in the elderly by as much as 40%, according to a new study. And the effect is even more pronounced for those who are more frail, say the researchers.

The US team, at Group Health Cooperative in Seattle, studied a group of 1740 people aged 65 or over, all of whom began the study with good cognitive function.

So don't just sit there, exercise! :)