Previous studies have suggested a causal relationship between physical activity and reduced risks of cognitive impairment in the aging population. Thorleif Etgen, from Technische Universitat (Munich, Germany), and colleagues studied 3,903 subjects, ages 55 and older, following them for a two-year period. Each was categorized as to physical activity (no activity, moderate activity [<3 times/wk], and high activity [3 times/wk]), and cognitive function was evaluated. At the beginning of the study, 418 participants (10.7%) had cognitive impairment. After two years, 207 (5.9%) of the remaining 3,485 unimpaired study participants developed cognitive impairment. Observing that the incidence of new cognitive impairment among participants with no, moderate and high activity at baseline was 13.9%, 6.7% and 5.1%, respectively, the researchers urge that: "Moderate or high physical activity is associated with a reduced incidence of cognitive impairment after 2 years in a large population-based cohort of elderly subjects. Physical activity can be performed by most elderly people but must be done correctly with the support of specialized personnel.

Thorleif Etgen; Dirk Sander; Ulrich Huntgeburth; Holger Poppert; Hans Förstl; Horst Bickel. "Physical Activity and Incident Cognitive Impairment in Elderly Persons: The INVADE Study." Arch Intern Med, Jan 2010; 170: 186 - 193.