Alzheimer's disease is the most common form of dementia, a general term used to describe severe cognitive decline.
Over the past few decades, much has been written about the protective effects on memory and cognitive function that learning a foreign language brings. So much so that many people think learning a foreign language may help prevent Alzheimer's disease.
Research shows, however, that this is not the case. What learning a foreign language can do, though, is delay the onset of the disease. And it can do so for up to five years.
Researchers from Iowa State University, Centre for Addiction and Mental Health, Toronto, Canada, and York University published a meta-analysis (a research process in which several independent studies are merged to calculate an overall effect) in 2021 in which they reviewed dozens of studies comparing both incidence and onset of Alzheimer's disease in monolingual and bilingual adults while controlling for confounding.
The researchers concluded that, even though the incidence rate was not statistically different in the two groups, the average age of onset was robustly delayed in the bilingual group.
The mechanism for this protective effect is not fully understood. The authors speculated that bilingualism "likely strengthens alternative functional circuits, which may be recruited to allow individuals with increasing amounts of Alzheimer’s pathology to present as cognitively normal."
But regardless, the data is clear: learning a foreign language does not prevent the incidence of Alzheimer's, but it contributes to cognitive reserve in a way that allows people to resist the progression of the disease.