Examining the relationship between multilingualism, age, and genetics to cognition across the lifespan: evidence from the Lifelines Cohort study

Aging is associated with a decline in cognitive functioning starting around the third decade of life (Ferguson et al., 2021). Different lifestyle factors have been found to contribute to the brain’s resilience against age-related cognitive decline, such as adhering to a healthy diet and engaging regularly in physical activity (Clare et al., 2017). Genetics have been found to play an important role in shaping aging trajectories. An example of a gene associated with aging is APOE ɛ4. Whereas younger APOE ɛ4 carriers tend to show enhanced cognitive performance, older APOE ɛ4 carriers have been found to exhibit accelerated cognitive decline and worse cognitive performance compared to non-carriers (Fan et al., 2019). Crucially, gene-lifestyle interactions have been identified (Klinedinst et al., 2020).

Multilingualism has been related to adaptations of the cognitive systems also affected by aging, suggesting it to be a cognition-enhancing lifestyle factor (Bialystok, 2017). Nevertheless, the positive association between multilingualism and cognition is debated, largely due to inconsistent findings across the lifespan. This, in turn, has been ascribed to several factors, such as the operationalization of multilingualism as a dichotomous variable and the fact that studies often did not control for other lifestyle factors that impact cognition (Leivada et al., 2021). Moreover, gene-lifestyle interactions have rarely been taken into account in multilingualism studies, despite the substantial evidence from the literature on other lifestyle factors.

The goal of this epidemiological study is to investigate the extent to which multilingual experiences moderate the effect of age on cognition across the adult lifespan in APOE ɛ4 carriers and non-carriers. We examined a sample of cognitively healthy adults from the Lifelines study - a population-based cohort study comprising data of 167.729 people living in the northern Netherlands (Sijtsma et al., 2022). The dataset includes cognitive, lifestyle and genetic data, and recently data from a language background questionnaire has been added. In our analysis, cognitive performance is assessed using the Cogstate Brief battery evaluating processing speed, visual attention, working memory and visual learning (Fredrickson et al., 2010). Based on the language background questionnaire, several multilingual experiences are evaluated, including second language (L2) age of acquisition, L2 proficiency, and degree of multilingual engagement (measured with language entropy scores (Gullifer & Titone, 2020)). Sex, physical activity, diet, and educational attainment are accounted for as nuisance covariates. APOE ɛ4 status is determined based on the genetic data available. Data analysis is currently ongoing (to be completed before June), with so far 12.000 participants included.

We predict enhanced cognitive performance as a function of multilingual engagement. We expect this to be stronger in older ages, as cognitive performance may be more compromised relative to younger ages in which subjects are still at peak cognitive performance (cf. Bialystok, 2017). Furthermore, we predict enhanced cognitive performance in younger APOE ɛ4 carriers and older APOE ɛ4 non-carriers (cf. Fan et al., 2019). With increasing age, we expect multilingual experiences to more prominently mitigate negative effects of APOE ɛ4 on cognitive performance.