Study at the Rush Alzheimer's Disease Center (716 dementia-free volunteers, average age of 82): one's level of activity can impact the risk for developing Alzheimer's--even in people in their 80s. Individuals in the bottom 10% of intensity of physical activity were 2.8 times as likely to develop Alzheimer's disease compared to those in the top 10%. An actigraph, a watch-sized device worn on the wrist, was used to measure physical activity. Interestingly, much of the recorded movements came from regular activities of daily living rather than formal exercise. The bottom line? Stay active! (Source)
Longitudinal study in eastern Finland started in 1970s: Of the 2000 people in the study, 76 had Alzheimer’s disease in 1998. Those who had been physically active in midlife (e.g., leisure-time physical activity that lasts at least 20-30 minutes and causes breathlessness and sweating) were less likely to have Alzheimer’s and other dementia. (Fields, Helen (writer). U S News and World Report. Reported October, 2005.)
Study of nearly 5,000 men and women over 65 years of age: those who exercised were less likely to lose their mental abilities or develop dementia, including Alzheimer's.
A five-year study at the Laval University in Sainte-Foy, Quebec suggests that the more a person exercises the greater the protective benefits for the brain, particularly in women. (The Franklin Institute.)