[Bilingualism as a factor in the protection of Alzheimer's disease: a systematic review]

Alzheimer's disease (AD) is the most prevalent type of dementia today, with an incidence estimated at 30% of the population over 85 years of age, which is why it represents a health problem in today's society.

To know if bilingualism can act as a protection factor for AD, thus increasing cognitive reserve.

We searched for studies in the PsychInfo, Pubmed, Psicodoc, Medline and PubPych databases, based on the combination of various terms related to the keywords. Finally, ten studies were included.

Seven of the ten selected studies suggest a significantly positive relationship between bilingualism and AD, although on the contrary two of the remaining studies find a partial relationship, where there is only a relationship in very specific circumstances (in the first one there is only one positive relationship when there is a low level of education, while in the second one there is only a relationship when more than two languages are spoken); only one of the studies found no significant relationship between bilingualism and AD.

The aforementioned studies have found a delay at the time of diagnosis or at the onset of clinically significant symptoms, between 4.5 years and 7 years; thus, bilingualism could be considered a contributing factor of the cognitive reserve and as a consequence a probable protection factor to prevent or slow the onset of AD and its subsequent progression.