In a study of bilingual people and dementia risk, researchers found that speaking more than one language can cut a population’s prevalence of dementia in half.
Researchers studying the link between bilingualism and dementia risk found more evidence that people who have spoken two languages regularly throughout their lives have enhanced cognitive reserve and greater resilience against the onset of dementia symptoms and cognitive decline.
“The prevalence of dementia in countries where more than one language is spoken is 50 percent lower than in those regions where the population uses only one language to communicate,” lead author Marco Calabria, professor at the Universitat Oberta de Catalunya Faculty of Health Sciences, said in a news release.
“We have seen that the more you use both languages and the better your language skills, the more neuroprotective advantage you have,” he said. “When something is not functioning well due to the disease, thanks to the fact that it is bilingual, the brain has efficient alternative systems for resolving the problem … In fact, active bilingualism is an important predictor of delay in the onset of symptoms of mild cognitive impairment — a preclinical phase of Alzheimer’s disease — because it contributes to cognitive reserve” — the brain’s resistance to cognitive damage or degeneration.
The study’s findings, published in Neuropsychologia, are aligned with previous research establishing the cognitive advantages to bilingualism and multilingualism. For example, a study of 325 nuns at the Sisters of Notre Dame showed that of the nuns who spoke four or more languages, only six percent developed dementia. Meanwhile, 31 percent of nuns who spoke only one language developed dementia.
A 2007 study of 184 people at a Toronto memory clinic found that the monolinguals in the sample had an average age of 71.4 years at the time of their onset of dementia, while the bilinguals were diagnosed at an average age of 75.5 years.
Another study by researchers in India published in 2013 found that monolinguals among its study cohort started displaying dementia symptoms four and a half years before people who spoke two or more languages, even after controlling for factors like gender and occupation.
By some estimates, there are fewer people in the world who speak only one language fluently than there are bilingual and multilingual people. And these latter groups outperform monolingual people in cognitive skills like selective attention and multitasking.
In their book, Becoming Fluent: How Cognitive Science Can Help Adults Learn a Foreign Language, authors Richard Roberts and Roger Kreuz write that if the benefits of being bilingual spill over to other aspects of cognition, “then we would expect to see a lower incidence of Alzheimer’s disease in bilinguals than in monolinguals, or at least a later onset of Alzheimer’s for bilinguals.”
“As encouraging as these kinds of studies are, they still have not established exactly how or why differences between bilinguals and monolinguals exist,” Roberts and Kreuz write. “Because these studies looked back at the histories of people who were already bilingual, the results can only say that a difference between the two groups was found, but not why that difference occurred. Further research is needed to determine what caused the differences in age of onset between the two groups.”
In an effort to add more nuance to that research, Calabria’s team established a bilingualism gradient: “from people who speak only one language but are passively exposed to another, to individuals who have excellent proficiency in both and use them indiscriminately on a day-to-day basis.”
“We wanted to discover the mechanism through which bilingualism contributes to cognitive reserve in cases of mild cognitive impairment and Alzheimer’s, and whether there were differences in terms of the benefit gained from different degrees of bilingualism, and not only between monolingual and bilingual people,” he said.
He and his colleagues took into account variables including age of acquisition of the second language, the extent to which each language is used, and whether the speaker would switch between languages in the same context, focusing on the population of Barcelona, where Catalan and Spanish languages are both in common use.
“We wanted to take advantage of this variability, and instead of comparing monolingual and bilingual people, we looked at whether in Barcelona, where everyone is more or less bilingual, there was a certain degree of bilingualism that had neuroprotective benefits,” he said.
The researchers recruited 63 cognitively healthy study participants, 135 participants with mild cognitive impairment such as memory loss, and 68 participants with Alzheimer’s in four hospitals in Barcelona and the metropolitan area.
To establish proficiency in Catalan and Spanish and ascertain each person’s degree of bilingualism, they used a questionnaire and then correlated the degree of bilingualism for each participant with the age of neurological diagnosis and the onset of symptoms.
They then asked participants to perform various cognition tasks, focusing executive control, which kicks in when we perform several actions at once, as previous studies have suggested that this is the source of the benefit of bilingualism or multilingualism.
“We saw that the people with a higher degree of bilingualism received a diagnosis of mild cognitive impairment later than those who were passive bilinguals,” Calabria said.
In the context of neurodegenerative diseases, he said, the executive control system of the brain could offset the symptoms of cognitive decline.
For future research, researchers will examine whether bilingualism could have a beneficial impact on the brains of people with similar neurodegenerative diseases such as Parkinson’s.
Roberts and Kreuz would remind those following the research that there are so many variables, from education level to income to social interaction, which may also affect a person’s susceptibility to the symptoms of dementia, that individual studies have sprawling limitations.
But: “Even if studying a foreign language is not a magical cure-all,” the write, “there is one thing it will do: It will make you a better speaker of a foreign language. Doing that confers a whole host of advantages we do know about.”