Study author Robert S. Wilson of the Rush University Medical Center in Chicago said the study involved 294 people. They were given tests that measured memory and thinking annually for about six years. They died at an average age of 89.
The researchers also answered a questionnaire about whether they read books, wrote and participated in other mentally stimulating activities during childhood, adolescence, middle age and at their current age.
After the study subjects died, their brains were examined at autopsy for evidence of the physical signs of dementia, such as lesions, brain plaques and tangles.
The research found people who participated in mentally stimulating activities both early and late in life had a slower rate of decline in memory compared to those who did not participate in such activities across their lifetime.
The study, published in the online issue of Neurology, found the rate of decline was reduced by 32 percent in people with frequent mental activity in late life, compared to people with average mental activity, while the rate of decline of those with infrequent activity was 48 percent faster than those with average activity.
"Based on this, we shouldn't underestimate the effects of everyday activities, such as reading and writing, on our children, ourselves and our parents or grandparents," Wilson said in a statement.