NHFT Libraries Health News: Being bilingual may slow the onset of dementia

Monday, 11 November 2013

Being bilingual may slow the onset of dementia

Being bilingual may slow the onset of dementia “Speaking a second language may delay dementia" BBC News reports. A study in the multi-lingual Indian city of Hyderabad found that those people with dementia who spoke two or more languages had a delayed onset of symptoms of around four and half years.

As the researchers point out, the city of Hyderabad provided a unique test bed for research. Due to historical and cultural reasons many residents speak at least two languages. This differs from other locations where bilingualism is associated with being an immigrant or educational status; both potential confounders in the field of dementia research.

The study involved a consecutive series of more than 600 Indian people with dementia who were assessed at a specialist dementia clinic. Just over half of them were bilingual, and the researchers compared age of onset of symptoms between bilingual and monolingual people. Bilingual people developed dementia around 4.5 years later.

An important limitation of the study is that the population of people referred to this specialist clinic may not be representative of the general population with dementia – either in India or elsewhere. Their average age of disease onset at 66 years was very young compared to most people who develop dementia in Western populations, and there was also a relatively low prevalence of Alzheimer’s while a higher prevalence of rarer dementia types, such as fronto-temporal dementia.

This study does not prove that learning a second language will delay or prevent the onset of dementia; but it cannot hurt. Keeping the brain active, learning about new cultures, and meeting new people should at least improve your mental wellbeing.

Where did the story come from?

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.

The study was published in the peer-reviewed journal Neurology.

The UK media’s reporting is variable. The news stories report the possible biological mechanisms by which increased brain activity may be protective which is certainly plausible, is unproven. But no media source seems to recognise the difficulty of generalising from this distinct population at a specialist dementia clinic who may not be representative of most people with dementia.

Also, the Mail Online’s assumption that learning two languages ‘could have a better effect than strong drugs’ is not supported by the research.

What kind of research was this?

The researchers say recent studies have suggested that speaking two languages (being bilingual) may delay the age at onset of dementia due to Alzheimer’s disease by up to five years

A possible mechanism being that the need to ‘juggle’ two or more languages in the one brain could enhance cognitive ability and delay symptoms of the disease.

However, as the researchers say, many questions remain, such as whether the effect could extend to other types of dementia, for example vascular dementia (a type of dementia caused by reduced blood flow to the brain).

Also, as the effect has so far mainly been demonstrated in studies of immigrant people, it is possible that other environmental factors associated with immigration could be confounding the relationship. Therefore the researchers chose to study a country where speaking more than one language is the norm – such as India.

Their study therefore involved reviewing the medical records of 648 Indian people who developed dementia, and comparing the ages that bilingual and monolingual people developed dementia, and other characteristics of the disease.

The main difficulty is that this study design cannot prove cause and effect.

Though the researchers have attempted to take into account other factors that could be confounding the relationship (such as educational level and occupation), it still cannot prove that the language difference is responsible for the differences in dementia characteristics between the two groups.

It is possible the influence of sociodemographic and other health and lifestyle factors have not been fully accounted for.

Another problem with this study is that it doesn’t show whether being bilingual is associated with a reduced risk of developing dementia, it only characterises differences within a group of people who all developed dementia.

A prospective cohort study collecting medical, cognitive, linguistic and social information is required to see if being bilingual is a protective factor against dementia.

What did the research involve?

The researchers reviewed the medical records for consecutive patients diagnosed with dementia at a specialist Memory Clinic in a hospital in Hyderabad, India between June 2006 and October 2012. All subjects had been examined by an experienced behavioural neurologist, assessed using valid diagnostic tools, and diagnosed using standard criteria.

For the present study, information was obtained from a reliable family member about the:

patient’s age
sex
age at onset of dementia (when first symptoms were observed)
educational status
occupation
rural or urban dwelling
family history of dementia
history of stroke
cardiovascular risk factors

Language history was assessed by interviewing a reliable family member. In Hyderabad, it is reported that the majority of the population are bilingual or may even speak three or more languages. Telugu is spoken by the majority of the population, who are Hindu, and a minority of the population who are Muslim speak Dakkhini gradually acquiring more functional roles in education, administration, and media, while Hindi, as the official national language is taught in schools.

During the study period, 715 people were diagnosed with dementia. After exclusion of those with missing sociodemographic or clinical data, 648 people were included in the study.

Monolingual and bilingual people were compared for age of onset and other characteristics of their dementia.

What were the basic results?

The 648 people (68% male) first presented at the clinic at an average age of 66.2 years, and had a duration of symptoms ranging from six months to 11 years. Thirty-seven percent had Alzheimer’s disease, 29% vascular dementia, 18% fronto-temporal dementia, 9% dementia with Lewy bodies, and 7% had mixed dementia. The majority of patients (86%) were literate and a quarter came from rural areas. Sixty percent of patients were bilingual: a quarter of all patients spoke two languages, a quarter spoke three languages, and just under 10% spoke four or more languages.

Overall the different dementia types were found with similar frequency among bilingual and monolingual people. Looking at age of onset, bilingual people were around 4.5 years older at the time of first dementia symptoms: 65.6 years compared to 61.1 years in monolingual people. The delay across the dementia types was 3.2 years in people with Alzheimer’s, six years in people with fronto-temporal dementia, and 3.7 years in vascular dementia.

The association between languages and age of onset remained significant even adjusting for other confounding factors that were more common among bilingual people, such as increased literacy, higher educational level, better education and urban dwelling.

There was no additional benefit to speaking more than two languages.

How did the researchers interpret the results?

The researchers say that theirs is the largest study to date to document a delayed onset of dementia in bilingual people, overall and in three dementia subtypes (Alzheimer’s, fronto-temporal and vascular dementias). Educational level is said to not be a sufficient explanation for the observed difference.

Conclusion

This consecutive series of people treated at a specialist dementia clinic in India found that people with dementia who are bilingual developed dementia later than people who were monolingual.

It is highly plausible that activities engaged in over a lifetime that increase our cognitive ability – such as understanding two or more languages – may have a protective effect against cognitive decline. However, this study cannot prove that being bilingual is directly protective against developing dementia.

This study only characterised differences within a group of people who all developed dementia, rather than looking at the whole population and seeing whether people who were bilingual were at reduced risk of developing dementia or developed dementia at an older age.

In addition, although the researchers have attempted to take into account other factors that could confound the relationship (such as educational level and occupation), it is possible that the influence of these and other factors has not been fully accounted for.

It is possible that our risk of developing Alzheimer’s in particular, but also possibly other types of dementia, may be influenced by a combination of sociodemographic, health and lifestyle factors.

Also, most of the information used in this study was collected from a family member said to be reliable, but it is uncertain whether this was the fact in all cases.

Another important point to be aware of is that the population of people with dementia referred to the specialist clinic in this study may not be representative of the general population with dementia – either in India or other countries. The average age of presentation to the clinic at 66 years was fairly young; the development of dementia in people of this age or younger is usually quite rare. Also looking at the types of dementia, the proportion with Alzheimer’s disease – which is the most common type of dementia – was very low at only 37%. In a generally representative population sample of people with dementia you would expect the proportion with Alzheimer’s to be around double this. Meanwhile, the proportions with the normally rare types of dementia – such as fronto-temporal dementia and dementia with Lewy bodies – were actually quite high.

Therefore this suggests that the population at this specialist clinic was perhaps more representative of those with less common types of dementia – rarer types and with earlier age of onset.

As such the results may not be generalisable to the majority population with dementia.

Overall this is interesting research into how being adept at more than one language may also keep our brains more active and so have some protective effect in preventing cognitive decline. However, this is not proven. Cohort studies in other population samples would be valuable.

With these limitations in mind, keeping your brain active by learning another language certainly won’t do you any harm.

Other ways that you may reduce your dementia risk are: