The Association of Multilingualism and Written Linguistic Ability with Mild Cognitive Impairment in the Nun Study

Abstract

Background: Multilingualism may be associated with enhanced cognitive function and reduced risk of mild cognitive impairment (MCI) due to enhanced cognitive reserve. Objectives: To investigate the association of multilingualism with overall MCI and MCI subtypes (non-amnestic versus amnestic). Methods: Participants from the Nun Study, a longitudinal study of 678 Catholic sisters in the U.S. aged 75+ years, were assessed for MCI in late life using standard neuropsychological tests and activities of daily living. Convent archives provided data on self-reported multilingualism from midlife and written linguistic ability (idea density and grammatical complexity) from early adulthood. Logistic regression models controlled for age, apolipoprotein E (a genetic risk factor), country of birth and education (n=384); sensitivity analyses (n=122) additionally controlled for written linguistic ability. Results: Speaking 4+ languages (but not 2 or 3) was associated with a significantly lower risk of overall MCI (OR: 0.32; 95% CI: 0.11-0.96) compared to monolinguals. However, this association weakened to non-significance after controlling for education. In the sensitivity analyses, multilingualism did not reduce the risk of overall MCI and its subtypes; however, written linguistic ability (specifically idea density) was significantly associated with a reduced risk of amnestic MCI, even after adjusting for education. Conclusion: By examining the number of languages spoken, in addition to examining written linguistic ability and controlling for education, this study contributes to the understanding of how these cognitively stimulating activities can act individually as well as in combination and how this may lead to a ceiling effect in their protective impact on MCI.