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Illiterate Adults Have Higher Dementia Prevalence, Study Finds

Article In Brief

Illiteracy was independently associated with a high risk of prevalent and incident dementia, according to a new report. The study authors suggest that illiteracy may place individuals on baseline testing to be that their initial cognitive test scores place them closer to diagnostic thresholds for dementia.

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In a study of older adults with limited formal schooling, those who were illiterate had a higher prevalence of dementia—as well as a higher rate of progression to dementia over the study period—than those who were literate, according to findings published in the November 13 online edition of Neurology.

The results—from a community longitudinal study of adults at least 65 years old who had no more than four years of schooling—underscore the association of illiteracy with dementia risk independent of someone's years of educational attainment, said Jennifer Manly, PhD, professor of neuropsychology at the Taub Institute for Research in Aging and Alzheimer's disease at Columbia University, and Miguel Arce Renteria, PhD, a post-doctoral fellow who is on her research team.

“Illiteracy increased the risk of both prevalent and incident dementia, even after taking into account potential demographic and medical confounders,” Dr. Manly said. “We also looked at how literacy relates to change in cognitive function over time. As expected, illiterate participants started the study with lower scores—for memory, language, and visuospatial functioning—compared with literate participants, but surprisingly, literacy was not associated with rate of cognitive decline.”

Dr. Renteria added that the findings point to the need for better vigilance among populations vulnerable to illiteracy. “Although the rates of illiteracy are low in developed countries and are being reduced in developing countries, there is still a large percentage of older adults that did not acquire literacy skills, and this is more likely among older racial/ethnic minorities and/or immigrant populations in the United States,” he said.

The study found no differences in race/ethnicity between literate and illiterate participants, for example, but a greater proportion of participants from the Dominican Republic were in the illiterate group.

“Clinicians should ask questions about early life educational experiences of their patients, not assuming that patients with low education have low literacy (and vice versa). Patients with low literacy may be at increased risk of developing dementia, and thus should be monitored accordingly.”

Study Design, Findings

Participants in the study were drawn from the Washington Heights-Inwood Columbia Aging Project, a prospective study of dementia in ethnically diverse neighborhoods in northern Manhattan. Participants were asked, “Did you ever learn to read or write?”—and were administered cognitive tests at one or more visits. Researchers included only those individuals who had up to four years of no schooling to avoid having effects confounded by participants' lifetime educational experiences and to avoid confusing a lack of opportunity for schooling with learning disability. Those who attained literacy with no formal schooling mostly did so in childhood through informal lessons from family members, though the questionnaires did not directly ask about this.

The analysis included data on 983 adults, gathered across three recruitment cohorts in 1992, 1999, and 2009. They were followed for an average of 4.1 years, with follow-up evaluations completed every 18 to 24 months. Participants completed a comprehensive neuropsychological battery assessing memory, language and visuospatial learning that has been validated for use among people with low literacy. Researchers recorded demographics including age, gender, years of schooling, race and ethnicity, country of origin, adult and childhood socioeconomic status, as well as medical risk factors including hypertension, diabetes, and heart disease.

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“Clinicians should ask questions about early life educational experiences of their patients, not assuming that patients with low education have low literacy (and vice versa). Patients with low literacy may be at increased risk of developing dementia, and thus should be monitored accordingly.”—DR. MIGUEL ARCE RENTERIA

“We also looked at how literacy relates to change in cognitive function over time. As expected, illiterate participants started the study with lower scores—memory, language, and visuospatial functioning—compared with literate participants, but surprisingly, literacy was not associated with rate of cognitive decline.”

—DR. JENNIFER MANLY

A consensus group of neurologists, psychiatrists, and neuropsychologists diagnosed dementia cases using all available clinical information.

Researchers found illiterate individuals were almost three times as likely to have dementia at baseline (at 35 percent) and incidence over time (at 48 percent) compared with people who were literate (18 percent and 27 percent, respectively). Being illiterate, they found, increased the odds of prevalent dementia by 2.35 (95% CI=1.70 to 3.26). The increased odds remained after adjusting for covariates, they found.

The odds for developing incident dementia were 1.95 times higher among the illiterate participants, researchers found. Illiteracy's effect was reduced slightly—to 1.63 times more likely—after adjusting for covariates (95% CI = 1.12 to 2.36).

Illiterate participants had worse initial scores on measures of memory, language and visuospatial learning, but their literacy status did not affect the slope at which these worsened, showing that the rate of decline did not seem to be affected by literacy status.

Researchers said the results suggest that the higher incidence of dementia among illiterate participants may be “because their initial cognitive test scores place them closer to a diagnostic threshold for dementia compared to literate participants.”

Their initial hypothesis was that literacy status would influence the rate of cognitive decline, but this did not turn out to be the case in this study, Dr. Manly said.

One reason, they wrote in the paper, is that this hypothesis was based on prior studies that looked at people with low literacy—a broader category than illiteracy—and prior studies were not restricted to those with limited years of schooling, so “it is possible that literacy skills only affect cognitive change if the entire ranges of educational attainment and literacy are considered.”

Also, this study included only those 65 or older, and it is possible that illiteracy's effects on rate of cognitive decline happens before that age, they wrote.

Researchers noted that literacy was associated with higher scores across multiple cognitive domains—not just those usually linked with reading or language skills.

“Throughout life, knowing how to read provides an important means of acquiring and structuring new knowledge that benefits not just language ability, but reinforces skills in working memory, visual memory, visuospatial processing and visuomotor skills,” they wrote. “The underlying mechanism for this generalized effect of literacy may be changes in cortical network organization and function.”

Future studies could examine whether literacy lowers risk of dementia “via brain reserve or brain maintenance,” such as increasing the size or resistance of brain structures to neuropathology, the researchers said.

“Reducing disparities in literacy and educational quality during childhood would thus be expected to promote cognitive health in later life, but this study does not allow us to conclude that illiteracy causes dementia, or that teaching an illiterate adult to read will reduce their dementia risk.”

—DR. PAUL BREWSTER

Expert Commentary

Robert S. Wilson, PhD, professor of neurological sciences at Rush Medical College, said the study “elegantly demonstrates that illiteracy dramatically increases risk of developing dementia in old age.”

“The study suggests that becoming literate—and acquiring formal education—may help prevent dementia in old age,” Dr. Wilson said. “The results show that the effect of literacy is through its association with level of cognitive function rather than rate of cognitive decline. This is entirely consistent with prior research on the level of educational attainment. Education/literacy enhance the development of cognitive ability but do not protect against cognitive decline in old age.”

Paul Brewster, PhD, who studies aging and lifelong health psychology and is a clinical neuropsychologist and adjunct assistant professor of psychology at the University of Victoria in British Columbia, said the results on the rate of decline were not surprising. “The finding of no association between literacy and the rate of cognitive decline is in keeping with the broader literature examining early socioeconomic influences on late life cognition,” Dr. Brewster said.

“This has been described as a ‘decline/dementia paradox,’ whereby early and mid-life risk factors for subsequent dementia diagnosis are poor and inconsistent predictors of decline in longitudinal studies. The interpretation described in this article—illiterate individuals are closer to cognitive and functional threshold for dementia diagnosis at their baseline—is reasonable and has often been used to explain this paradox.”

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“The results show that the effect of literacy is through its association with level of cognitive function rather than rate of cognitive decline. This is entirely consistent with prior research on level of educational attainment. Education/literacy enhance the development of cognitive ability but do not protect against cognitive decline in old age.”—DR. ROBERT S. WILSON

Dr. Brewster emphasized that care should be taken when assessing cognition among the illiterate—performance on the Mini-Mental Status Examination and similar measures can reflect baseline ability rather than cognitive decline.

“Psychometric evidence of cognitive impairment should thus be corroborated by a detailed clinical interview and collateral from informants that have a close and longstanding relationship with the patient. Cultural norms around what constitutes normative activities of daily living functioning should also be considered, especially for racial/ethnic minorities,” he said.

The study, he said, adds to the growing literature showing early-life socioeconomic and educational experiences as “robust predictors” of dementia risk in old age.

“Reducing disparities in literacy and educational quality during childhood would thus be expected to promote cognitive health in later life,” he said, “but this study does not allow us to conclude that illiteracy causes dementia, or that teaching an illiterate adult to read will reduce their dementia risk.”

Disclosures

Drs. Manley, Renteria, Wilson, and Brewster had no competing interests.

Link Up for More Information

• Rentería MA, Vonk JM, Felix G, et al. Illiteracy, dementia risk, and cognitive trajectories among older adults with low education https://n.neurology.org/lookup/doi/10.1212/WNL.0000000000008587?. Neurology 2019; Epub 2019 Nov 13.