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 fronto-temporal 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 versus 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 American Academy of Neurology 2013.

 

The  Edinburgh University study was duplicated by Nizam's Institute of Medical Sciences in Hyderabad in India and was (at least to this reviewer's eyes) most effectively reported by NHS Choices⁽¹⁾ which in more detailed accuracy informed us that  "The study was carried out by researchers from Nizam’s Institute of Medical Sciences, Osmania University, Yashoda Hospitals and the University of Hyderabad, India, and University of Edinburgh. Funding was provided by the Department of Science and Technology, Cognitive Science Research Initiative, Government of India."  It should come as no surprise that the Indian emphasis is on Indian funding, whereas references to the Edinburgh study emphasise the UK funding.  Actually, both are accurate.

The clear conclusion would seem to be that being able to speak more than one language may help you think more clearly in later life, even if you’ve learned the second language as an adult.

Thomas H. Bak of the University of Edinburgh Centre for Cognitive Ageing and Cognitive Epidemiology, the study’s lead researcher, said previous studies had shown that “bilinguals” who suffered dementia began showing symptoms four to five years later than people who spoke only one language, but it was not clearly established whether the mastery of a second language extended brain activity or really favour people who already have healthier brains.

In this latest study, older bilinguals performed better on cognitive tests than monolinguals, even when they had not scored better on intelligence testing decades earlier. That means that, at least in part, learning another language does predict brain health in old age.   Bak said "Probably the causality is going in both directions, but we showed that there is certainly an effect of bilingualism that cannot be explained by previous differences.”

The earlier study was carried out on participants from the Lothian Birth Cohort 1936 (1,091 people) who took an intelligence test in 1947 at the age of 11, and were retested between 2008 and 2010 when they were in their 70s (853 people).

This cohort was unique in that they were native English speakers of European origin who were born, raised and living in and around Edinburgh. No immigrants were included.

The researchers said that by using this birth cohort, they were able to question whether learning a second language influences later cognitive performance after adjusting for childhood intelligence.

Intelligence testing consisted of a series of assessments, including:

   a range of fluid-type general intelligence tests, including letter-number sequencing a range of memory tests

  speed of information testing reading tests that examined the pronunciation of 50 irregular English words as part of the National Adult Reading Test (NART)

  verbal fluency testing, where participants were asked to say as many words as possible beginning with the letters C, F and L, with a one-minute timeframe for each letter

  the Moray House Test, which mainly tests verbal reasoning skills

It is unclear if the intelligence tests performed were the same as those carried out on participants when they were 11.

Bilingualism was assessed using a questionnaire where participants were asked whether they had learned any languages other than English, how many, and at what age.

They were also asked how often they used the languages (daily/weekly/monthly/less than monthly/never) across three areas: conversation, reading and media.

The researchers were interested in:

  the age of additional language acquisition (never/early/late);

  the number of languages (monolingual/bilingual/multilingual);

  the frequency the additional language(s) were used (no second language/no active use/active use)

In their analysis, the researchers adjusted the results for childhood intelligence, age at time of testing, sex and social class.

What were the basic results?

Of the 853 participants who completed the intelligence retesting between 2008 and 2010, 262 people (30%) reported having learned at least one other language to a level that allowed them to communicate.

Of these, 195 learned the second language before the age of 18 (though only 19 [2%] before the age of 11) and 65 learned it after this age.

The researchers report that 160 people knew two languages (bilingual) and 85 people knew three or more languages (multilingual).

The researchers found that people who spoke two languages (bilingual) performed significantly better than predicted from their baseline cognitive abilities. The strongest associations were seen in tests of general intelligence and reading.

The cognitive effects of bilingualism showed a consistent pattern, affecting reading, verbal fluency and general intelligence to a higher degree than memory, reasoning and processing speed.

Other results of note are described below.

Age of language acquisition

For early language acquisition, significant positive associations were found in the tests for general intelligence and reading. For late language acquisition, significant positive associations were found in the tests of general intelligence, processing speed and reading. 

Number of languages

Bilingualism showed a significant positive association with tests of reading, while multilingualism showed significant positive associations with general intelligence, reading and verbal fluency.

Frequency of use

For passive bilingualism (no active use of the language for the past five years), the main associations were seen in the tests of general intelligence, reading and verbal fluency. For active bilingualism (use of the language in the past five years), the main associations were seen in the tests of general intelligence and reading.

However, there was a significant association between childhood intelligence and performance at the age of 73 for the active group on the Moray House Test – a significant effect of active bilingualism was only found for lower childhood intelligence.

In terms of the type of bilingualism, different effects were seen for early versus late acquisition depending on childhood intelligence. Overall, people with high intelligence appeared to benefit more from early acquisition, and those with low intelligence from late acquisition, but neither group showed negative effects.

Knowing three or more languages produced stronger associations than knowing two languages. There was little difference seen in the comparison between active and passive bilinguals, which the researchers say might be a result of the low frequency of use of the second language, even in active language users. 

 How did the researchers interpret the results?

The researchers concluded that their results suggest a protective effect of bilingualism against age-related cognitive decline independent of childhood intelligence, including in those who acquired their second language in adulthood.

In discussing the findings, lead researcher Dr Thomas Bak is reported in the media as saying: "These findings are of considerable practical relevance. Millions of people around the world acquire their second language later in life. Our study shows that bilingualism, even when acquired in adulthood, may benefit the ageing brain." 

Conclusion

Overall, this study suggests an association between cognitive functioning later in life and having learned another language or languages.

A strength of the research is that it took into account childhood intelligence, which previous studies are not reported to have accounted for.

There remain some important limitations, however:

    Bilingualism was assessed using a questionnaire and not by proficiency testing, which may have biased the results. It is possible that some participants may have overestimated their ability to speak languages other than English.

   The researchers adjusted the results for childhood intelligence at age 11, but this may not have fully accounted for the person's overall cognitive ability and educational level in later childhood and adulthood. Also, despite adjusting for age at testing, sex and social status, there may be other hereditary, health and lifestyle factors at play that, taken overall, make it difficult to know whether acquiring and using a second language in itself has a direct and independent effect on cognitive ability.

   The researchers report that the birth cohort was homogenous, so findings from this study may not be generally applicable to a different group of people (people who have migrated to another country, for example). Also, the study was carried out among a relatively small group of people based in Edinburgh, so the results should be interpreted with caution when generalising to other populations.

   The study did not assess whether participants had cognitive impairment or dementia, so it cannot tell us whether being bilingual is protective against the development of these conditions.

While it may seem a commonsense proposition that keeping the brain active will protect against dementia, the evidence is inconsistent. Various brain training exercises have been studied with varying degrees of success.

However, there is evidence that keeping the mind active at any age does improve mental wellbeing, whether it's learning a new language, teaching yourself to cook, or going to a museum. [See author's footnote]

But co-author Viorica Marian said: "People do crossword puzzles and other activities to keep their minds sharp. But the advantages we've discovered in dual language speakers come automatically simply from knowing and using two languages."

 

The UK Foreign Office is reported as having an unofficial ranking system of language difficulty based on how long it takes staff to become reasonably proficient in speaking the language. Relatively easy languages, taking around 600 hours to learn, include French, Dutch and Italian.  More challenging languages, taking around 1,100 hours to learn, include Polish, Russian and Farsi.  Extremely difficult languages, taking more than 2,000 hours to learn, include Arabic, Cantonese and Korean. Foreign and Commonwealth Office