Dementia is the largest cause of dependency and disability in older adults, affecting millions of people worldwide. It has been suggested that bilingualism, where an individual speaks two or more languages, may delay the development of dementia. But what evidence is there for this?
My recent paper, published in the Journal of European Psychology Students, reviewed the evidence, using a series of nine studies published in scientific journals. Participants in the studies spoke a variety of languages (e.g. English, French, Spanish) and differed in terms of participant characteristics (i.e. education status and immigration status). The methods used between studies also differed substantially, with some examining medical records of patients already diagnosed with dementia, and others following healthy older adults over a period of several years.
The evidence for a delayed onset and diagnosis of dementia in bilinguals was mixed. Some studies found that bilinguals were diagnosed with dementia several years later than monolinguals, even after controlling for demographic variables (such as age and education status). However, others found no significant differences between bilinguals and monolinguals.
The review therefore explored whether language factors, such as age of acquisition and proficiency could account for the inconsistencies in findings. From this, it was suggested that lifelong bilingualism may protect against dementia, if both languages are used frequently throughout life. However, it appears that bilingualism is not associated with a later onset or diagnosis of dementia if the second language is learned later on in life or used infrequently.
Becoming bilingual in adulthood in order to delay the development of dementia is therefore unlikely to be successful. However, it is important to note that this conclusion is tentative at present, and would require further experimental study before stronger conclusions can be drawn. This should therefore not deter adults who wish to become bilingual, particularly as there are a magnitude of other benefits that come from learning a second language.
A more concerning finding was that results also appeared to depend on the methods used. In studies which examined medical records of patients already diagnosed with dementia, it was often found that bilingualism protected against dementia. However, in prospective studies, which followed healthy older adults for a number of years to see who developed dementia, there was often no effect of bilingualism. Ideally, findings using differing methods should yield consistent findings, highlighting a need for further research to resolve these inconsistencies.