It turns out that the answer is very simple:

The four key factors involved in preventing mental decline were found to be exercise, education, social activity and not smoking.

That’s the results of a study published in the journal, Neurology.

While the fact that exercise can help keep your mind healthy into old age is not new, this was a long term study of people in their 70s (when the study began). When 30% of participants had no decline in mental capacity, researchers began looking for common factors. That is when they found that this group all had at least some high school education (high school graduates did better), didn’t smoke, had social activities, and exercised at least once a week.

Even better news, these things are inexpensive, and require no prescription.