More Evidence Bilingualism Delays Dementia

November 07, 2013

More evidence that speaking a second language may protect against dementia has come from a study conducted in India.

The study, published online November 6 in Neurology, was conducted by a team led by Suvarna Alladi, DM, from Nizam's Institute of Medical Sciences, Hyderabad, India.

"This study provides the strongest evidence yet that speaking more than 1 language delays the development of dementia," coauthor Thomas H. Bak, MD, from the University of Edinburgh, United Kingdom, commented to Medscape Medical News. "We can't say we have proven the effect, but this is the largest and most thorough study conducted on the subject in the most appropriate population. It would be extremely surprising if the results were not real."

He explained that 2 previous studies, both conducted in Toronto, Canada, have suggested that bilingualism might postpone dementia. However, most of the bilingual participants were immigrants with very different cultural backgrounds than members of the monolingual group, which introduced a high degree of confounding.

"Ideal Location"

Dr. Bak pointed out that they wanted to look at a more homogeneous population. "We chose Hyderabad, in India, as it has large numbers of both monolingual and bilingual people, and it is a native population with few immigrants. It is an ideal location for this type of study."

The study involved 648 patients with dementia diagnosed at a specialist clinic, 391 of whom were bilingual. The age at onset of first symptoms was compared between monolingual and bilingual groups.

Results showed that overall, bilingual patients developed dementia 4.5 years later than those who spoke only 1 language. The effect was consistent across the different types of dementia and was also independent of other potential confounding factors such as education, sex, occupation, and urban vs rural dwelling of participants.

"These findings are stunningly similar to those from the Canadian studies. So we have 2 very different places showing exactly the same effect," Dr. Bak noted.

"I would say that you should definitely bring your children up bilingual if you can. There is already a large amount of evidence that bilingual children have cognitive advantages; they do better at school. The effect in childhood is well-established. What is not so well known is whether it lasts until old age. Our results suggest it is."

He pointed out that the study was large enough to look at different types of dementia and that they found the same effect in all 3 major types: Alzheimer's, vascular, and frontotemporal. "We didn't see it in dementia with Lewy bodies, but we only had a few patients with this diagnosis, so that is not surprising," he added.

Education Not a Factor

Dr. Bak noted that the argument has been made that the effect of bilingualism on dementia may purely be a result of better education, but he made the point that in Hyderabad, a significant portion of the population has not been to school and is illiterate, but many of these people still speak 2 languages.

"We found an even larger difference in age of dementia onset in the illiterate patients: 65 [years] in the bilingual group vs 59 in the monolingual patients, a 6-year difference, which strongly suggests the effect has nothing to do with education."

On the mechanism behind this effect, the researchers explain that switching between languages is good brain training. "The constant need in a bilingual person to selectively activate one language and suppress the other is thought to lead to a better development of executive functions and attentional tasks," the authors write.

To Medscape Medical News, Dr. Bak commented: "There are different ways of mental training, but bilingualism combines many of these things including sound, visual memory, processing function, and social cognition. It's like working on 10 processes for the price of 1."

Unlike previous studies, in the current study, there was no advantage in terms of dementia of speaking more than 2 languages. Dr. Bak suggested this may have been because in this area of India, bilingual individuals are constantly switching between the 2 languages. "You cannot spend a day in Hyderabad without being exposed to 2 or 3 different languages, so the brain is switching all the time. This may be all the brain needs, so in these circumstances there may not be any advantage of speaking more than 2 languages."

There are still some questions left unanswered, however. Dr. Bak noted that they do not know whether the second language has to be acquired early or if the same results would be seen if it were learnt later in life. Also, it is not clear how much the second language has to be practiced.

"In our study in Hyderabad, many people speak 2 languages, and the bilingual people will probably use both languages daily. But we don't know if the same results would be achieved if a second language was learnt as a child but not spoken regularly in later life."

The study was supported by the Department of Science and Technology, Cognitive Science Research Initiative, Government of India. Dr. Bak has disclosed no relevant financial relationships. Full conflict-of-interest information is available in the published report.

Neurology. Published online November 6, 2013. Abstract

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