Beneficial effect of bilingualism on Alzheimer's disease CSF biomarkers and cognition

Abstract

Bilingualism as a component of cognitive reserve has been claimed to delay the onset of Alzheimer’s disease (AD). However, its effect on cerebrospinal fluid (CSF) AD-biomarkers has not been investigated. We assessed cognitive performance and CSF AD-biomarkers, and potential moderation effect of bilingualism on the association between age, CSF AD-biomarkers, and cognition. Cognitively healthy middle-aged participants classified as monolinguals (n ¼ 100, nCSF ¼ 59), early (n ¼ 81, n CSF ¼ 55) and late bilinguals (n ¼ 97, nCSF ¼ 52) were evaluated. Models adjusted for confounders showed that bi- linguals performed better than monolinguals on digits backwards (early-bilinguals p ¼ 0.003), Judgment of Line Orientation (JLO) (early-bilinguals p ¼ 0.018; late-bilinguals p ¼ 0.004), and Trail Making Test-B (late-bilinguals p ¼ 0.047). Early bilingualism was associated with lower CSF total-tau (p ¼ 0.019) and lower prevalence of preclinical AD (NIA-AA classification) (p ¼ 0.02). Bilingualism showed a moderation effect on the relationship between age and CSF AD-biomarkers and the relationship between age and executive function. We conclude that bilingualism contributes to cognitive reserve enhancing executive and visual-spatial functions. For the first time, this study reveals that early bilingualism is associated with more favorable CSF AD-biomarker profile.