doi:10.1038/nindia.2013.161 Published online 27 November 2013
A bilingual person is likely to develop dementia at a later age than a monolingual person, according to neurologists studying the association between bilingualism and the age of onset of dementia and its subtypes .
The study — the largest so far documenting a delayed onset of dementia in bilingual patients and the first one to show it separately in different dementia subtypes — concluded that overall, bilingual patients developed dementia 4.5 years later than monolingual ones.
The bilingual group was drawn from the same environment as the monolingual one. The results were, therefore, free from the confounding effect of immigration. In all, the researchers examined case records of 648 patients with dementia (391 of them bilingual) diagnosed in a specialist clinic. They compared the age at onset of first symptoms and compared the results between monolingual and bilingual groups. They examined the influence of number of languages spoken, education, occupation, and other potentially interacting variables.
This is also the first study reporting a bilingual advantage in those who are illiterate, suggesting that education is not a sufficient explanation for the observed difference. It demonstrates a delay in 3 different types of dementia: Alzheimer disease (AD), frontotemporal (FTD) and vascular (VaD).