1. Bilingualism or multilingualism has protective effect on dementia onset: is there any evidence? A systematic review
Yadav AK, Yadav J, Kumar P, Sagar R, Bhasin R, Misra S, Kumar A, Prasad K
Department of Neurology
All India Institute of Medical Sciences, New Delhi
RESULTS:
INTRODUCTION:
In past decade there has been renewed interest in bilingual or multilingual and its effect of dementia.
Emerging literature suggests that speaking two or more languages may significantly delay the onset of dementia.
Mechanism is unknown , however cognitive reserve is suggested.
Cognitive reserve may involve reorganisation and strengthening of neural networks that enhances executive control, evidence from the fMRI and DTI studies in children collaborate the hypothesis.
However recently two large cohort studies have refuted the protective effect of bilingualism on delay in dementia. Hence this systematic review look into the evidence available till date for protective effect of multilingualism on dementia
On literature search we found 82 article which had bilingual or multilingual and dementia or MCI or Alzheimer disease in their abstract. We further found 9 article looking for references.
Out of these article only nine studies studied association of delay in onset of dementia and bilingualism and multilingualism.
Two case series one comprising of two patient and other forty four patients respectively.
One nested case control study
Four case control study
Two cohort study
Findings of these studies in tabulated form is shown below
S. No
Place
Author and Year
Setting
Sample size
Criteria for bilingualism
Remarks 1
Luxembourg
Perquin et 2013
Community setting
232
Subjects practicing 2 or more language (no definition given)
Protective Odds ratio 0.3( ). Progressing from 2 to 3 languages, associated with 7 fold protection 0.14 ( ) 2
Canada
E. Bialystok et al 2007
Clinic
184
Patients spent the majority of their lives,
at least from early adulthood, regularly using at least two languages.
Found significant delay in dementia in bilinguals 3
F. I. M. Craik et al 2010
211
-do- 4
H.Chertkow et al 2010
632
significant delay in onset of dementia in multilingualism not bilingualism 5
India
S. Alladi et al 2013
648
Bilinguals were defined as persons with an ability
to meet their normal communicative demands in two or more languages when interacting with speakers of any or all of these languages. In addition, these individuals spent
the majority of their lives, from late childhood and early
adulthood, regularly using at least two or more languages
Bilingualism was associated with a
significant delay in age of onset of dementia 6 US
Sanders et al 2012
Community based
1779
Non-native English speaking population
No statistically significant association between n-NES status and incident dementia (HR= CI ) 7
Zahodne et al 2014
1067
Self reported and validated with wide range achievement test (WRAT-3) in subpopulation.
bilingualism was not independently associated with rates
of cognitive decline or dementia conversion
OBJECTIVES:
To review the evidence available for protective effect on dementia of bilingualism and multilingualism
METHODS:
Electronic databases (PubMed) were searched until Feb 2015 for all studies evaluating effect of bilingualism or multilingualism on dementia. The key words used were bilingualism, multilingualism, dementia, MCI, Alzheimer’s disease.
All published manuscripts up until and including letters, case reports, epidemiological studies, previous review and abstracts were included.
The retrieved studies were examined thoroughly to assess their appropriateness. study
Search terms-‘bilingualism’, ‘multilingualism’, ‘dementia’, ‘MCI’, ‘Alzheimer’s disease
In addition, reference lists were also examined to acquire additional relevant articles
INCLUSION & EXCLUSION CRITERIA:
Studies were reviewed if:
Analytical studies
Case control studies showing odds ratio of bilingualism or multilingualism with dementia or onset of dementia
Cohort studies showing association of bilingualism or multilingualism with dementia or onset of dementia
Case reports
Review article on bilingualism or multilingualism
Previous review article on effect of bilingualism or multilingualism on onset of dementia.
Neuro-imaging studies on bilingualism or multilingualism
Editorial by experts on bilingualism or multilingualism
Letter to editor on bilingualism or multilingualism
Chapters in books were excluded.
Unpublished article were not searched
CONCLUSION:
Though biological plausibility and analogy for higher cognitive reserve among bilingual or multilingual exist through fMRI and DTI studies yet the current evidence of bilingualism or multilingualism on protective effect on dementia is inconclusive and further large multi-centric cohort studies are recommended