People who want to stay sharp in later life should follow a number of simple lifestyle choices, according to a study.
Exercise, education, social activity and not smoking have all been identified as key factors involved in preventing mental decline.
Researchers from the University of California at San Francisco looked at more than 2,000 men and women aged in their 70s and 80s and found those who exercised moderately or vigorously at least once a week were 30% more likely to "stay sharp" than people who did not.
The study, published in the journal Neurology, also showed a person with a good education was nearly three times more likely to maintain their mental faculties than someone who was less educated.
Those who did not smoke were nearly twice as likely to remain quick witted than those addicted to nicotine, and people who lived with someone, or who regularly worked or volunteered, were 24% more likely to avoid mental deterioration in later life.
Study leader Dr Alexandra Fiocco said: "To this day, the majority of past research has focused on factors that put people at greater risk to lose their cognitive skills over time, but much less is known about what factors help people maintain their skills."