Researchers studied 983 adults over 65 years of age living in the New York area of Washington Heights who had four or less years of school.
Visiting participants' homes, scientists performing tests of memory, language, and visual or spatial abilities, During these visits, they were diagnosed with dementia based on standard criteria.
Illiterate participants performed worse than these tests.
In establishing basic measures, those who have never learned to read or write are almost three times more likely to have dementia than those who can read.
And among those who did not have dementia at the start of the study, the illiterate section of the cohort was twice as likely to develop it.
One reason for brain decline, writes the authors, is that those who do not learn to read have a "lower range of cognitive function" than those who are literate.
The findings are part of a long-term study of aging
Jennifer Manley, a professor of neuropsychology at Columbia University and senior author of the study, told CNN that scientists have observed a cohort of adults over 65, many of the most diverse environments in the Washington Heights area since 1
Over the past three decades, they have studied 6,500 New Yorkers as they aged, she said.  While it has long been recognized that educational attachement can be linked to better health outcomes, the primary purpose of the study is to determine how literacy may or may not be related to one's ability to maintain brain health through your golden years.
For example, many of the illiterate adults in Washington Heights came from the Dominican Republic and said they might have to drop out of school to work.
She says more research is needed to confirm the results of her team, but they could create a public health case for early school leavers to enroll in adult literacy courses help maintain protection against dementia.
Policymakers need to take this into account, says scientist
Manley said the study had implications for how countries think about their educational policies.  "The reason for not going to school is due to Dominican education policy," she said.
Manly said that in the US, policymakers must take into account the fact that "educational quality shapes brain health in the aftermath of life."
"Increasing opportunities for children and adults to acquire literacy can be protective of brain health later in life," she said.
Manly likens the positive effects that learning to read can have on the mind of the positive effects that exercise can have on the body.
"For people and families, health behaviors should include education," she said.