Characterization of Bilingual Mexican Americans among a Community Dwelling Cohort: An HABS-HD Study

Introduction: Bilingualism has been increasingly studied in the context of neuroprotection particularly as it relates to cognitive decline. Despite higher rates of English/Spanish bilingualism, Mexican Americans also experience a higher risk of cognitive decline related to Alzheimer’s disease (AD) and Alzheimer’s Disease Related Dementias (ADRDs) as compared to Non-Hispanic Whites. Few studies to date have broadly examined the link between bilingualism and specific demographic, cognitive, and biomarkers among this ethnic group.The aim of this study is to examine the relationship between language status (monolingual/bilingual) on select demographic, cognitive, and AD specific blood biomarkers among this racial/ethnic group.

Methods: Data were analyzed on n=890 Mexican Americans from the The Health & Aging Brain Study - Health Disparities (HABS-HD) study. Participants completed a clinical interview, which includes a self-report of language status (monolingual/bilingual) as well as various neuropsychological tests and an informant interview in order for clinicians to determine cognitive and functional status. Plasma amyloid (A), tau (T), and neurofilament light chain NfL blood biomarkers were assayed using the ultra-sensitive Single molecule array (Simoa) technology. Demographic characteristics were generated utilizing independent t-tests or chi square analyses for continuous and/or categorical variables. ANCOVAs were conducted with covariates of age, sex, and education for cognitive test performance and A/T/(N) blood biomarkers split by language status (monolingual, bilingual) as well as by cognitive status (cognitively unimpaired, cognitively impaired).

Results: Of the n=890 Mexican Americans, n=393 self reported as monolingual and n=497 as bilingual. Among monolinguals, 70% were diagnosed as cognitively unimpaired, 20% with mild cognitive impairment (MCI), and 10% with Dementia while among bilinguals, 78% received a diagnosis of cognitively unimpaired, 17% with MCI, and 5% with Dementia. Regarding neuropsychological testing, bilingual individuals performed significantly better across measures of global cognition, attention, and processing speed (ps<0.001). While examining blood biased biomarkers, a trending significance of higher total tau was found among bilinguals compared to monolinguals. When separated by cognitive status, total tau was higher among bilingual Mexican Americans who were cognitively unimpaired (p=0.044). Higher Aβeta 40 levels were found to be significantly associated with reduced performance on measures of attention, processing speed, and executive functioning among bilinguals who were cognitively unimpaired (ps<0.001). Among bilinguals with cognitive impairment, higher total tau levels were associated with lower performance on a measure of working memory (p=0.001) and higher NfL levels were associated with lower performance on measures of global cognitive screening measure and working memory (ps=0.001).

Discussion: As rates of AD and ADRDs increase in Mexican Americans, their bilingualism may be advantageous in delaying this pathology. Bilingualism is differentially related to cognitive and AD biomarkers. Better understanding the relationship between bilingualism and these markers might be informative regarding potential protective effects for this at risk group.