International Alzheimer's Day: bilingualism protects against cognitive decline

By: Marco Calabria, UOC – Open University of Catalunya

According to data from the World Health Organization, the prevalence of Alzheimer's disease will triple between now and 2050. And that forecast poses a major public health challenge.

There are many variables that influence the increase in cases, from the increase in life expectancy to the incidence of new risk factors. The good news is that modifying any of these factors can slow the upward curve, or at least delay the age of onset of cognitive symptoms of neurodegenerative diseases.

Without going any further, taking good care of our emotions, maintaining a good network of social relationships and intensifying our mental activity will stop Alzheimer's. And the same seems to do certain cognitive activities. Among them, bilingualism. Does speaking two languages ​​really act as a protective factor? What type of bilingualism and what mechanisms promote an advantage?

Clinical trial

Conflicting results on bilingualism and Alzheimer's

In 2004, Ellen Bialystok and colleagues from York University in York, Canada, published a study that became famous for suggesting that bilingualism delayed the diagnosis of Alzheimer's disease. These researchers compared the clinical data of 184 patients, half of whom were bilingual and the other half monolingual. The results were surprising: bilinguals had a four-year lead, that is, they received a diagnosis later than monolinguals. After that work, other researchers have replicated similar results in bilingual communities like India and Scotland.

However, there are also many who have failed to demonstrate that speaking two languages ​​protects against cognitive decline. Furthermore, according to some reviews, around 40% of studies do not show positive benefits of bilingualism in delaying the onset of neurodegenerative diseases.

This conclusion is not surprising, since the literature on the benefits of bilingualism in healthy people is not consistent, and in several studies the effect is negligible.

Not all bilinguals are the same

In the face of these conflicting results, the crucial question to ask is whether there are any factors that influence the benefits of speaking two languages. If so, it would explain that sometimes they are robust and sometimes not.

After all, it should not be forgotten that bilingualism is a heterogeneous concept that includes several variables such as the age of acquisition of the second language, the use made of it, linguistic competence, and the frequency with which a specific speaker alternate their two languages. That makes a simplistic binary classification of monolingual vs. bilingualism.

The suspicion that it is the degree of bilingualism that generates an advantage was what motivated our recent study, carried out in collaboration with several hospitals in Catalonia, the Pompeu Fabra University of Barcelona and the Neuropsychology and Functional Neuroimaging group of the Jaume I University from Castellón de la Plana.


To find out which were the crucial characteristics of bilingualism in the context of cognitive reserve, that is, as a protective factor against cognitive deterioration, we worked with 200 Catalan-Spanish bilingual patients.

We started with an advantage since in reality sociolinguistics In Catalonia there is some variability in the speakers, ranging from what we could call "active" to those who are "passive". The assets are distinguished by a profile of high linguistic competence, balanced use and with frequent changes between the two languages. The passive ones, on the contrary, would be the speakers who have a knowledge of their second language (Catalan), due to exposure to it, but who do not usually practice it.

This way of classifying bilinguals gave us a gradient, a continuum. The results of the analyzes revealed that the degree of bilingualism would be correlated with the age of onset of symptoms and diagnosis. That is, the higher the grade (more "active"), the higher the age at which symptoms of cognitive decline appear.

A relevant fact is that this advantage is independent of other cognitive reserve factors that moderate the effect of protection against cognitive deterioration, such as the level of schooling, status socioeconomic or mental, social and leisure activity.

How is this bilingual advantage explained?

A second aspect that we investigated was the specific mechanism that determines bilingual advantage. To do this, we collected data on the performance of the participants in various cognitive memory and executive control tasks. Executive control is a set of skills that helps us efficiently manage the change between tasks, as well as filter out irrelevant information and plan our actions. We took into account to change the language and monitor the interference of a language that we do not speak are activities that the bilingual brain performs continuously and in close contact with executive control.

In this sense, the results of our research indicated that active bilinguals perform better than passive bilinguals in tasks that involve the management of information that involve cognitive conflict.

In conclusion, everything indicates that the active use of the two languages ​​allows for more efficient executive control. And, as suggested by the theories of cognitive reserve, if we have high cognitive efficiency it is possible that it can compensate for the deficits cognitive factors associated with a disease neurodegenerative.

All of this means that the symptoms of cognitive decline appear later – or to a lesser degree neurodegeneration-, as we demonstrated in a previous study that we carried out with a group of researchers from the Jaume I University.

The next challenges will be to extend this research to other pathologies neurodegenerative like the disease of Parkinson's.

Marco Calabria, Professor of Health Sciences Studies (Master of Neuropsychology), UOC – Open University of Catalunya

This article was originally published on The Conversation. Read the original.