But before you invest in those online linguistic courses, caveat emptor. The study, of 211 people with probable AD was retrospective and cross-sectional in design, making it unclear if it was the bilingualism per se that delayed onset of dementia, or some other characteristic of polyglots. The researchers ruled out obvious factors, including immigration status (had no effect on age at onset) and the amount of formal education, which has been shown to protect against dementia (bilingual patients had less formal education). Nevertheless, they note that a prospective study would yield more definitive results.

Another recent study of language and dementia tells a slightly different story. Also conducted in Canada, it found that multilingualism, but not bilingualism, protects against AD in non-immigrant populations, whereas bilingualism is protective in immigrant populations (see Chertkow et al., 2010).

If multilingualism can protect against dementia, then it may be because it has laid some groundwork that helps neurons communicate in the face of encroaching pathology. “Our interpretation...is that bilingualism is a cognitively demanding condition that contributes to cognitive reserve in much the same way as do other stimulating intellectual and social activities,” write Craik and colleagues. The downside for monoglots (who are outnumbered by polyglots according to Wikipedia) is that for some it may be too late to brush up on that second language. Craik’s study only looked at people who were bilingual for the majority of their lives—since at least early adulthood. It is not clear if adopting another language in mid-life would bring any benefit. Quel dommage!—Tom Fagan.

Reference:
Craik FI, Bialystok E, Freedman M. Delaying the onset of Alzheimer disease: Bilingualism as a form of cognitive reserve. Neurology 2010 November 9;75:1726-1729. Abstract