Effects of bilingualism on the age of onset and progression of MCI and AD: Evidence from executive function tests.

Abstract

Previous articles have reported that bilingualism is associated with a substantial delay in the onset of both Alzheimer's disease (AD) and Mild Cognitive Impairment (MCI). The present study reports results from 74 MCI patients and 75 AD patients; approximately half of the patients in each group were bilingual. All patients were interviewed to obtain details of their language use, onset of their condition, and lifestyle habits. Patients performed three executive function (EF) tests from the D-KEFS battery (Trails, Color-Word Interference, Verbal Fluency) on 3 occasions over a period of approximately 1 year. Results replicated the finding that bilingual patients are several years older than comparable monolinguals at both age of symptom onset and date of first clinic visit. This result could not be attributed to language group differences in such lifestyle variables as diet, smoking, alcohol consumption, physical activity, or social activity. On the first testing occasion, performance on the EF tasks was generally comparable between the language groups, contesting arguments that bilinguals wait longer before attending the clinic. Finally, EF performance tended to decline over the 3 sessions, but no differences were found between monolinguals and bilinguals in the rate of decline.

The Protective Effect of Cantonese/Mandarin Bilingualism on the Onset of Alzheimer Disease

“…The results of this study demonstrated that Cantonese/Mandarin bilingual AD patients were significantly older when AD symptoms began than Cantonese or Mandarin monolingual patients, which is consistent with the previous reports of other language pairs [1-3]. The bilinguals also had an older age than both groups of monolinguals at the first clinic visit.…”

“…The multivariate linear regression analyses showed that relocation history was not an influential factor associated with the onset age of AD, but the p values reached marginal significance ( p = 0.082), suggesting that relocation history may have the potential to delay the onset of AD. Even though the term “relocation” in this study seems similar to “migration” in the study by Bialystok et al [3], they are substantially different in meaning. Relocation in this study was defined as moving within China.…”

“…It may be that relocation in China partly led the patients to learn to speak both Cantonese and Mandarin. In comparison, the study by Bialystok et al [3] showed that a history of migration does not delay dementia onset. Bhugra and Becker [18] suggested that migration could enrich environment exposures to increase the CR, but often involves a loss of socioeconomic status and increased rates of mental illness.…”

“…Patients who spoke only one language were defined as monolinguals. The criterion developed by Bialystok et al [3] for bilingualism was adopted, with slight modification: “the criterion for bilingualism was that individuals had spent the majority of their lives, beginning at least in early adulthood, speaking two languages fluently – ideally daily, but at least weekly.” As this study focused on the relationship between Cantonese/Mandarin bilingualism and the onset age of AD, we replaced “two or more languages” in Bialystok’s criterion by “two languages.”…”

“…Recently several studies have found strong evidence that bilingualism can delay the age of onset of Alzheimer disease (AD) [1-3]. The interpretation of the protective effect of bilingualism against AD is that the use of two languages can enhance cognitive reserve (CR) by switching between the two languages, and increasing the efficiency of the executive control system [4].…”