For several years, experts have advised people to exercise their brains to conflict the memory loss related with Alzheimer's disease and other disorders leading to cognitive decline. For example, they suggest computer games, playing cards or chess, doing cross-word puzzles, and simply maintaining active social interactions. And such brain exercises do seem to result in modest benefits.

Lot of small observational studies had suggested that physical activity can also help maintaining memory power and reduce the threat of cognitive decline. Reports in 2006 on two large prospective studies supported the benefits of exercise on cognitive function. Participants on those studies were 65 years of age or older and free of cognitive impairment, and they were followed for an average of about 6 years. One study of 1,740 men and women from Seattle found that the risk of dementia was 38 percent lower in those who exercised 3 or more times a week compared to those who exercised fewer than 3 times a week. The authors concluded that their results “suggest that regular exercise is associated with a delay in onset of dementia and Alzheimer disease.”

The second study of 3,375 men and women found that participants who were in the group with the highest expenditure of physical activity had a 50 percent lower likelihood of developing dementia than those with the lowest level of physical activity.

Similarly, an article in a recent Journal of the American Medical Association described the results of a randomized trial of aerobic exercise in 138 Australian subjects older than age 50. On their entry, the participants did not have objective evidence of dementia. When assessed after 18 months for signs of Alzheimer disease and cognitive decline, subjects who had been assigned to the exercise group showed a modest improvement in cognition compared to non-exercisers.

None of these or other studies have shown that physical exercise has a truly dramatic effect on preservation of mental function. Nonetheless, the results suggest that healthier aging and prevention or delay in the development of dementia may be added to the many other benefits of regular exercise.