Being well versed in multiple languages can help thwart the development of dementia, a study done at the University of Waterloo has found.

Dementia generally refers to a decline in mental ability serious enough to disrupt everyday life. There are over a hundred causes of dementia, the most common being Alzheimer’s disease. Alzheimer’s is estimated to affect 5.8 million Americans of all ages in 2019 and is the sixth leading cause of death in the U.S.

Led by Suzanne Tyas, a public health professor at Waterloo, the research team examined the health outcomes of 325 Roman Catholic nuns who were members of the Sisters of Notre Dame in the United States. The data was drawn from a larger, internationally recognized study examining the Sisters, known as the Nun Study.

Between nuns that spoke four or more languages and nuns that spoke only one, the former experienced a 6 percent incidence of dementia while the latter a 31 percent. Being in between and speaking two or three languages did not have much effect in lowering the risk in this study. However, this differs from previous research.

"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 Tyas. "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."

Tyas added, "Language is a complex ability of the human brain, and switching between different languages takes cognitive flexibility. So it makes sense that the extra mental exercise multilinguals would get from speaking four or more languages might help their brains be in better shape than monolinguals."

When the researchers examined 106 of the nuns’ writing samples and compared it to the broader findings, they found that the ability to write a language influenced an individual’s risk of developing dementia. For example, idea density -- the number of ideas expressed concisely in written work -- helped reduce the risk even more than multilingualism.

"This study shows that while multilingualism may be important, we should also be looking further into other examples of linguistic ability," said 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."