Does Bilingualism Protect against Cognitive Decline? Cross-sectional and Longitudinal Evidence from Ethnically Diverse Older Adults

The benefits of bilingualism for maintaining late-life cognition remain controversial, with mixed evidence across populations. We conducted the first large-scale, longitudinal investigation of bilingualism in an ethno-racially diverse cohort, with 4,140 participants at baseline (1,013 bilingual) and 1,760 individuals (522 bilinguals) with up to four follow-ups. Cognitive outcomes included dementia status and scores on executive function and episodic memory factors, with ethnicity and gender as potential moderators. Longitudinal analyses revealed that bilingualism predicted slower episodic memory decline irrespective of ethnicity, gender, education, baseline age, and practice effects. However, the cross-sectional associations between bilingualism and cognition varied by ethnicity. While these ethnicity-related differences in cognitive benefits of bilingualism may reflect other sociocultural factors, the longitudinal benefit of bilingualism on memory is more consistent with neuroprotective benefits. Overall, this study provides novel insights into how bilingualism shapes cognitive aging and highlights its potential for promoting late-life cognitive reserve.