Illiteracy Tied to Dementia Risk

Illiteracy was linked to a higher risk of prevalent and incident dementia, but not to more rapid cognitive decline, a longitudinal community study showed.

Older adults who never learned to read or write were nearly three times as likely to have dementia at baseline as people who were literate, according to Jennifer Manly, PhD, of Columbia University Vagelos College of Physicians and Surgeons in New York City, and colleagues.

And of those who were dementia-free at baseline, people who were illiterate were twice as likely to develop dementia over time, they reported in Neurology.

"It is important to understand what early life factors, especially those that can be modified, increase dementia risk," Manly told MedPage Today. "Current rates of illiteracy in the United States are relatively low; nevertheless, there are around 32 million adults who are illiterate."

"Physicians and other healthcare professionals should ask about educational and literacy background of their patients," and should be aware that people who are illiterate may be at increased risk of developing dementia and might need to be monitored, she added.

Because attempts to develop effective drug treatments for dementia so far have been unsuccessful, there's increasing interest in how lifestyle factors might protect against cognitive decline. This includes education, which "often is discussed in the context of cognitive reserve," observed Thomas Bak, MD, of the University of Edinburgh in Scotland, who was not involved with the study.

"Education is one of the most discussed potential protective factors, but its effects are not universal and can be limited to certain groups," he told MedPage Today. "So this paper addresses an important and still unresolved issue."

In their study, Manly and colleagues followed 983 adults from the Washington Heights-Inwood Columbia Aging Project (WHICAP) in northern Manhattan. Participants had an average age of 77 and all had ≤4 years of schooling; many were born and raised in rural areas of the Dominican Republic where access to education was limited.

A total of 237 people reported they were illiterate, responding "no" to the question "Did you ever learn to read or write?" At each follow-up visit of 18 to 24 months, participants had functional, cognitive, and medical data reviewed and a dementia diagnosis made. Evaluations were administered in the participants' preferred language, English or Spanish. The average time in the study was 4.10 years, with a range of 0 to 23 years.

Overall, participants who were illiterate had lower childhood socioeconomic status and greater cardiovascular disease risk burden than literate participants. They also had a greater proportion of dementia cases at baseline (35%) than those who were literate (18%). After adjusting for covariates, participants who were illiterate had nearly three times higher odds of prevalent dementia (OR 2.65, 95% CI 1.55-4.50).

Similarly, individuals who were illiterate were more likely to develop dementia over time (48%) than those who could read or write (27%), though the effect of illiteracy was less after factoring in covariates (HR 1.63, 95% CI 1.12-2.36).

In multiple domains -- memory, language, and visuospatial functioning -- participants who were illiterate had lower initial scores than literate participants, but literacy status did not affect the rate of change over time.

"This study investigates a complex topic -- complex as it is difficult to tease apart potential interrelations between factors like literacy, education level, quality of education received, and learning disabilities, and how those factors might later influence cognitive test performance and dementia diagnosis in aging," noted Allison Kaup, PhD, of the Neurology Center of Southern California in Carlsbad, who was not involved with the study.

"It is interesting that in this study, illiteracy was associated with increased risk of new dementia diagnosis during the course of the study, but there was no association between illiteracy and rate of decline in cognitive performance," Kaup told MedPage Today. "This unexpected pattern seems to highlight the need for further advances in the field to address how to best measure and detect cognitive decline and diagnose dementia among individuals with low literacy."

The study had several limitations, Bak noted. It did not assess executive functions, which are "known to play a crucial role in cognitive reserve and dementia," he said. It also does not address reverse causality: "Does literacy improve cognition, or are more intelligent people, even if they come from low socio-economic status, more likely to learn to read?"

Literacy also is highly dependent on the country or society people live in, Bak pointed out. "In Western countries, we assume that everybody should be literate, so most information -- like events, but also health tips and warnings -- are written, and those who cannot read miss out on all this," he said.

"In a society with a lot of illiterates, there might be other ways of conveying important information so even without being literate, one is not left outside," he continued. "We cannot assume that the effects of literacy will be the same across the whole world."

Another limitation is that the study did not ask how or when literate study participants learned to read and write, the researchers noted. Literacy was determined by self-report in response to a single question, and it was not clear whether some participants knew how to read but not write, which might lead to differential dementia risks.

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