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Research links being bilingual with delay in dementia onset

Nov. 8, 2013

Good news for people who speak more than one language: new research links being bilingual with a delay in the onset of dementia.

Earlier studies had linked bilingualism to delayed onset of dementia from Alzheimer’s disease, but a new study shows delayed onset of other types of dementia as well. The new research also showed this link in people who are illiterate, separating possible effects of bilingualism from the cognitive benefits of education.

Researchers at Nizam’s Institute of Medical Sciences in India and the University of Edinburgh in the U.K. studied the case records of 648 dementia patients. All of the patients were treated in a hospital’s specialist memory clinic in Hyderabad, India. About one-third of the patients were women. The study subjects had a range of different types of dementia, including Alzheimer’s disease dementia, vascular dementia, frontotemporal dementia, dementia with Lewy bodies and mixed dementia.

More than half of the study subjects spoke more than one language: 26.2 per cent spoke two languages, 25 per cent spoke three languages, and 9.1 per cent spoke more than three languages. Most of the patients were literate, but 14.1 per cent could not read and write.

The study was carried out in an area of India where many languages are spoken among the local population. In this area, bilingualism was not linked to immigrant populations as it might be in some other areas.

The researchers looked at how old the patients were when they developed dementia (age of onset). The average age of dementia onset was 66.2 years, but onset age ranged from 32 to 92 years in individual patients.

They compared age of onset in the patients who spoke more than one language to those who spoke only one. They found that bilingual patients developed dementia 4.5 years later than patients who spoke only one language. This difference was significant even after accounting for factors such as education, literacy, sex, occupation, type of dementia and family history.

There was also a difference in age of onset for several individual types of dementia. Bilingual patients developed Alzheimer’s dementia 3.2 years later than monolingual patients, frontotemporal dementia six years later, and vascular dementia 3.7 years later.

The researchers also looked at age of dementia onset in illiterate patients who had no formal education. In this group, the bilingual people developed dementia six years later, compared to those who only spoke one language.

There was no difference in age of dementia onset between people who spoke two languages and people who spoke three or more languages.

The study results suggest that speaking more than one language may have a protective effect against developing dementia. The researchers note that being bilingual means making constant mental switches between languages. This switching may help improve some types of brain function, including attention and executive function, which guides things like organization and planning.

Previous research has shown that several other factors are also associated with delayed dementia onset. These include education and taking part in activities that are intellectually stimulating. It’s believed that these factors improve the brain’s resistance to cognitive decline.

The study was published in the journal Neurology on Nov. 6, 2013.


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