How Do You Solve a Problem Like Dementia?

Is multilingualism the key to warding off cognitive decline? Researchers turned to the famous "Nun Study" for some new insights.


The ability to speak four languages or more could lower a person’s chances of developing dementia, according to a University of Waterloo study.

Speaking many languages may help prevent dementia by helping build resistance to cognitive decline, as well as sharpening neural networks in the brain through extra stimulation and challenge.

The evidence remains mixed, but the authors of the University of Waterloo study say the questionable quality of previous research and differences in the study populations may explain this. For these reasons, they were keen to work with a more uniform population, to level out other socioeconomic and environmental factors that could have an effect.

So, they sourced data on 325 religious sisters aged 75+ from a larger, internationally-recognized longitudinal study nicknamed ‘The Nun Study’.

“The Nun Study is unique: It is a natural experiment, with very different lives in childhood and adolescence before entering the convent, contrasted with very similar adult lives in the convent,” said lead author Suzanne Tyas, a health professor at the University of Waterloo in a press release.

“This gives us the ability to look at early-life factors on health later in life without worrying about all the other factors, such as socioeconomic status and genetics, which usually vary from person to person during adulthood and can weaken other studies.”

Four languages seems to be the benchmark for benefits

The sisters underwent routine cognitive assessments by gerontologists who conducted tests like the Mini-Mental State Exam, a 30-point questionnaire commonly used in clinical settings. For a diagnosis of dementia, researchers required measurable declines in the activities of daily living, like eating or using the washroom, in tandem with cognitive challenges like memory issues.

The prevalence of multilingualism among the sisters was determined using 1983 convent data sourced from the School Sisters of Notre Dame. At the time, the sisters reported their language skills for the purpose of determining international mission placements with occupations including teaching roles.

Abilities ranged from one to five languages, and since only a small portion of the cohort spoke four or five languages, they were bundled together as one category.

Researchers also took into account data on age, education, occupation, and writing samples. With the writing samples, the team looked for idea density and grammatical complexity as measures of ability. They defined idea density as the average number of ideas expressed per ten words.

Researchers found that around 6% of the study participants who spoke four or more languages developed dementia, compared to 31% of monolingual participants. Speaking two or three languages did not appear to be advantageous in this context, but it may be that higher levels of multilingualism would have led to a more active use of their abilities.

“[A sister’s] job posting and regular teaching duties may have been chosen specifically because they were highly capable in many different languages, and thus were placed into situations where they more regularly and actively made use of their linguistic abilities,” say the authors.

Idea density may be more significant than multilingualism

Interestingly, when researchers compared the influence of idea density to their larger findings, they found it had an even more powerful effect than multilingualism. Speaking many languages can improve our general abilities with language and literacy skills, but this finding suggests there may be more than one route to get there.

“This study shows that while multilingualism may be important, we should also be looking further into other examples of linguistic ability,” commented Tyas.

“In addition, we need to know more about multilingualism and what aspects are important — such as the age when a language is first learned, how often each language is spoken, and how similar or different these languages are. This knowledge can guide strategies to promote multilingualism and other linguistic training to reduce the risk of developing dementia.”

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Barry is a journalist, editor, and marketer for several media outlets including HeadStuff, The Media Editor, and Buttonmasher Magazine. He earned his Master of the Arts in Journalism from Dublin City University in 2017 and moved to Toronto to pursue a career in the media. Barry is passionate about communicating and debating culture, science, and politics and their collective global impact.