Bilingualism delays dementia in India, too

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Suvarna Alladi et al., "Bilingualism delays age at onset of dementia, independent of education and immigration status", Neurology 2013:

Objectives: The purpose of the study was to determine the association between bilingualism and age at onset of dementia and its subtypes, taking into account potential confounding factors.

Methods: Case records of 648 patients with dementia (391 of them bilingual) diagnosed in a specialist clinic were reviewed. The age at onset of first symptoms was compared between monolingual and bilingual groups. The influence of number of languages spoken, education, occupation, and other potentially interacting variables was examined.

Results: Overall, bilingual patients developed dementia 4.5 years later than the monolingual ones. A significant difference in age at onset was found across Alzheimer disease dementia as well as frontotemporal dementia and vascular dementia, and was also observed in illiterate patients. There was no additional benefit to speaking more than 2 languages. The bilingual effect on age at dementia onset was shown independently of other potential confounding factors such as education, sex, occupation, and urban vs rural dwelling of subjects.

Conclusions: This is the largest study so far documenting a delayed onset of dementia in bilingual patients and the first one to show it separately in different dementia subtypes. It is the first study reporting a bilingual advantage in those who are illiterate, suggesting that education is not a sufficient explanation for the observed difference. The findings are interpreted in the context of the bilingual advantages in attention and executive functions.

The basic finding has been Out There for several years, e.g. Elen Bialystok et al., "Bilingualism, Aging, and Cognitive Control: Evidence From the Simon Task", Psychology and Aging 2004; Ellen Bialystok et al., "Bilingualism as a protection against the onset of symptoms of dementia", Neuropsychologia 2007. Previous LL coverage includes "What bilinguals tell us about mind and brain", 2/19/2011; "The bilingual advantage",  6/1/2011.

This new study is especially important for the reasons explained in this passage:

These questions can be addressed by studying populations in which bilingualism forms part of everyday life of the autochthonous population. Such a situation exists in India, a country characterized by an exceptional linguistic diversity. Several aspects of Indian bilingualism are important in the context of this study. First, bilingualism does not tend to be associated with immigration. Languages are usually acquired simultaneously and used in parallel and language switching is very common. Furthermore, bilingualism in India is contact-based and motivated by socialization processes and is therefore found even among those who are illiterate. Based on this unique social and linguistic setting, we aimed to study the association between bilingualism and age at dementia and its subtypes, taking into account potential confounding factors.

In the subject population for previous studies, bilingualism has been associated with immigration, so that bilinguals and monolinguals generally have different life histories, cultural backgrounds, and even genetics. This raises the concern that effects attributed to bilingualism might actually be the result of a correlated factor, such as childhood diet or whatever.

In the Indian study, bilingualism has quite different (and rather varied) socio-cultural associations:

In Hyderabad, the majority of the population can be considered as bilingual and many speak 3 or even more languages. Telugu is spoken by the majority group who are primarily Hindus, whereas the language of a minority group of Muslims is Dakkhini. English is gradually acquiring more functional roles in education, administration, and media. In addition, Hindi is spoken as the official national language and is taught at school level. Thus, most people in Hyderabad are exposed to Telugu and Dakkhini in informal contexts and Hindi and English in formal contexts. The patterns of language use in Hyderabad have been systematically studied and are well documented.

It's reassuring to see that the apparent delay in symptom onset due to bilingualism is essentially identical to those found in Bialystok et al. 2007:

On comparing bilingual with monolingual cohorts,bilinguals were found to be 4.5 older at the time ofoccurrence of the first symptoms of dementia: 65.6 years in bilinguals as opposed to 61.1 years in monolinguals.

 

 

 

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7 Comments »

  1. bks said,

    November 9, 2013 @ 10:07 am

    Does this work if the second language is COBOL?

    –bks

    [(myl) Only if the first language is FORTRAN.]

  2. Kenny Easwaran said,

    November 9, 2013 @ 12:26 pm

    This research seems to suggest that out of those who eventually get dementia, the bilingual people tend to get it later. Do we know anything about the fraction of the population that tends to eventually get dementia, and whether that is affected by bilingualism?

    [(myl) The earlier research suggests that the the delay in symptom onset is due to "cognitive reserve" -- if this is correct, then the prevalence of the underlying pathology is not affected, just the level of symptom expression for a given degree of neural degeneration.

    According to "Alzheimer's Fact and Figures", estimates from the Chicago Health and Aging Project are that:

    * One in eight people age 65 and older (13 percent) has Alzheimer’s disease.
    * Nearly half of people age 85 and older (45 percent) have Alzheimer’s disease.
    * Of those with Alzheimer’s disease, an estimated 4 percent are under age 65, 6 percent are 65 to 74, 44 percent are 75 to 84, and 46 percent are 85 or older.

    CHAP did not calculate prevalence for other dementias.]

  3. Jon said,

    November 9, 2013 @ 5:14 pm

    These studies refer to age of onset of symptoms, and as myl says the suggested reason for the delay in bilinguals is cognitive reserve. The same reason is given for the delayed onset in people with university education. But the corollary is that the decline is swifter in those with cognitive reserve, since the endpoint of physical degeneration of the brain is the same, whether or not cognitive reserve delayed the onset.

  4. hanmeng said,

    November 9, 2013 @ 9:52 pm

    A somewhat off-topic anecdote: I knew an American woman who suffered from senile dementia (beginning in her 80's). In the later stages she didn't recognize her husband or children, but was still able to readily converse in the French she had learned when young.

  5. ET said,

    November 10, 2013 @ 12:02 pm

    How hard is it to find monolingual people in India?

  6. Adam Funk said,

    November 10, 2013 @ 3:15 pm

    @bks:

    I can't help but think of XKCD 297.

  7. naddy said,

    November 16, 2013 @ 12:54 pm

    So Luxembourg should have a later average onset of dementia than most other countries in Western Europe. Does it?

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