Bilingualism for delaying the onset of Alzheimer's disease: a systematic review and meta-analysis.

OBJECTIVE: To assess the effects of bilingualism compared to monolingualism on the clinical manifestation of Alzheimer's disease. METHODS: We searched the databases: MEDLINE, The Cochrane Central Register of Controlled Trials, Embase and LILACS, and searched by hand and in gray literature for studies published before September 2019. The quality of included studies was assessed using the Newcastle-Ottawa Scale. Two reviewers independently searched for studies, extracted data, and performed the quality assessment. RESULTS: Eight studies were included in this review. Data from meta-analyses suggest that bilingual individuals with Alzheimer's disease exhibit symptoms (694 participants; mean difference (MD) (4.05 years; 95% CI: 1.87-6.22 and are diagnosed later (1012 participants; MD 2.0 years; 95% CI: 0.08-3.92) than monolingual participants. CONCLUSION: Bilingualism may delay the manifestation of symptoms and diagnosis of Alzheimer's disease. Further studies with more rigorous methodology are needed to improve the precision of the results.