Does Bilingualism Delay the Development of Dementia?

Abstract

It has been suggested that bilingualism (where individuals speak two languages) may delay the devel- opment of dementia. However, much of the research is inconclusive. Some researchers have reported that bilingualism delays the onset and diagnosis of dementia, whilst other studies have found weak or even detrimental e ects. This paper reviews a series of nine empirical studies, published up until March 2016, which investigated whether bilingualism signi cantly delays the onset of dementia. The article also explores whether the inconsistent ndings can be attributed to di erences in study designs or the de nitions of bilingualism used between studies. Based on current evidence, it appears that lifelong bilin- gualism, where individuals frequently use both languages, may be protective against dementia. However, becoming bilingual in adulthood or using the second language infrequently is unlikely to substantially delay onset of the disease.

Full text

School of Psychology, University of Leeds, Leeds, UK
amy.atkinson@live.co.uk
Atkinson, A. L. (2016). Does Bilingualism Delay the Development
of Dementia?
Journal of European Psychology Students,
7(1),
43–50, DOI: http://dx.doi.org/10.5334/jeps.375
journal of european
psychology students
efpsa
LITERATURE REVIEW
Does Bilingualism Delay the Development of Dementia?
Amy L Atkinson
It has been suggested that bilingualism (where individuals speak two languages) may delay the devel-
opment of dementia. However, much of the research is inconclusive. Some researchers have reported
that bilingualism delays the onset and diagnosis of dementia, whilst other studies have found weak or
even detrimental eects. This paper reviews a series of nine empirical studies, published up until March
2016, which investigated whether bilingualism signicantly delays the onset of dementia. The article
also explores whether the inconsistent ndings can be attributed to dierences in study designs or the
denitions of bilingualism used between studies. Based on current evidence, it appears that lifelong bilin-
gualism, where individuals frequently use both languages, may be protective against dementia. However,
becoming bilingual in adulthood or using the second language infrequently is unlikely to substantially delay
onset of the disease.
Keywords: bilingualism; dementia; degree of bilingualism; language prociency; age of acquisition
Introduction
Dementia is a neurodegenerative disorder that results
in cognitive decline and a marked deterioration in the
capacity to function independently (American Psychiatric
Association [APA], 2013). Patients experience memory
problems, such as difficulty recognising familiar faces or
places (APA, 2013). In addition, individuals also frequently
present with impairments in other cognitive domains,
such as language or attention (APA, 2013). The most com-
mon type of dementia is Alzheimer’s disease (AD; Ott et al.,
1995; World Health Organization, 2015), where proteins
gradually build in the brain to form plaques and tangles
(Alzheimer’s Society, 2014a; Price & Morris, 1999). This
eventually leads to the death of cells and loss of brain tis-
sue, which causes cognitive decline (Alzheimer’s Society,
2014a). Other types of dementia include vascular demen-
tia, which is caused by cell death resulting from reduced
blood flow to the brain (Alzheimer’s Society, 2014b), and
frontotemporal dementia, which occurs due to cell death
in the frontal and temporal regions of the brain and the
pathways connecting them (Alzheimer’s Society, 2013).
Dementia is the largest cause of dependency and disa-
bility in older adults, affecting approximately 47.5 million
people worldwide (WHO, 2015). It also produces large eco-
nomic burdens, almost matching those caused by cancer,
heart disease and stroke combined (Wimo, Jönsson, Bond,
Prince, & Winblad, 2013). These individual and societal
costs are set to rise rapidly in coming years with cases of
dementia predicted to triple by 2050 due to population
ageing (Roberts & Petersen, 2014; WHO, 2015). As current
treatments for dementia are poor, research has recently
shifted, with an aim of discovering methods to delay or
prevent the onset of the illness (Gold, 2015).
Although controversial, some research has demon-
strated that higher workplace complexity and educational
attainment is associated with a delayed onset of demen-
tia (Andel et al., 2005; Bennett et al., 2003; Sattler, Toro,
Schönknecht, & Schröder, 2012; Valenzuela, & Sachdev,
2006). This is thought to occur due to an increase in
cognitive reserve, which refers to an enhanced ability to
adaptively use resources to mitigate damage to the brain
(Guzmán-Vélez & Tranel, 2015; Meng & D’Arcy, 2012;
Nithianantharajah & Hannan, 2009; Stern, 2002; Stern,
2009). This enhanced cognitive reserve is proposed to
delay the clinical manifestations of dementia, thus allow-
ing individuals to function independently for longer
(Gold, 2015). Recently, it has been suggested that bilin-
gualism, which refers to the ability to speak two languages,
may also delay the development of dementia. Substantial
evidence has been found to suggest that speaking two lan-
guages alters the brain, resulting in enhanced executive
control and cognitive functioning (Abutalebi, Canini, Della
Rosa, Green, & Weekes, 2015; Bialystok, 2011; but see Paap
& Greenberg, 2013). Based on this, it has been suggested
that bilingualism may also enhance cognitive reserve, pro-
viding protection against neurological damage and thus
delaying the onset of dementia (Abutalebi, Guidi, et al.,
2015; Bialystok, 2011).
However, inconsistent findings have been reported. This
paper will therefore review studies which have investigated
whether bilingualism delays the onset of dementia. It will
also consider whether differences in study designs and
the definitions of bilingualism used between studies can
explain the inconsistent findings reported. This review

Atkinson: Does Bilingualism Delay the Development of Dementia?44
will not provide an in-depth discussion of the mechanisms
thought to link bilingualism with a delayed onset of
dementia, but interested readers should refer to Gold
(2015) or Perani and Abutalebi (2015). Several reviews
have previously been conducted in this area (Bialystok,
Craik, & Luk, 2012; Gold, 2015; Perani & Abutalebi, 2015),
but these are either out of date given the high number
of recent publications, or do not specifically investigate
whether bilingualism delays the development of demen-
tia and the factors which may affect the relationship.
Search Strategy
PsycINFO and Google Scholar were searched for relevant
articles in English published up until March 2016. The
following search strings were used: ‘bilingualism AND
cognitive reserve’ and ‘bilingualism AND dementia’. Only
original studies were included. Studies which investi-
gated associations between bilingualism and the develop-
ment or progression of other health conditions, such as
strokes, were excluded. Studies that investigated whether
bilingualism is associated with slowed progression of
dementia were also excluded, as this review was primarily
interested in exploring whether bilingualism delays onset
of the disease. Nine studies were found which met the
criteria. These are outlined in Table 1 below.
Data synthesis
The first of these studies was conducted by Bialystok
et al. in 2007. They used medical notes and interviews
to investigate whether the onset age of dementia and
the first appointment to a memory clinic in Canada sig-
nificantly differed between monolinguals and bilinguals.
Individuals were defined as bilingual if they had “spent
the majority of their lives, at least since early adulthood,
regularly using at least two languages” (Bialystok et al.,
2007, p. 460). Bilinguals were diagnosed with the disorder
and experienced symptom onset significantly later than
monolinguals. These associations were present despite
heterogeneous factors between groups which should have
benefitted the monolinguals. The monolingual group
had on average received a higher level of formal educa-
tion (12.4 years, compared to 10.8 years in the bilingual
group), a factor which has been suggested to increase cog-
nitive reserve and potentially delay the onset of dementia
(Bennett et al., 2003; Meng & D’Arcy, 2012; Sattler et al.,
2012). In addition, a much higher number of the bilingual
group were immigrants (87%, compared to 14% of the
monolinguals). As many of these immigrants arrived from
Europe after World War II, it is likely they were exposed to
more stressful life events than the non-immigrants, which
is a known risk factor for dementia (Chertkow et al., 2010;
Gollan, Salmon, Montoya, & Galasko, 2011; Guzmán-
Vélez & Tranel, 2015; Machado et al., 2014). Nevertheless,
despite these factors, a significant difference was present
between groups, leading the authors to conclude that
bilingualism markedly delays the development of demen-
tia (Bialystok et al., 2007).
Critics, however, argue that the higher levels of immi-
grants within the bilingual group may have actually
favoured the bilinguals (Craik, Bialystok, & Freedman,
2010; Guzmán-Vélez & Tranel, 2015). Although stressful,
migration requires learning and adaption to a new envi-
ronment, an experience which is cognitively stimulating
(Guzmán-Vélez & Tranel, 2015). Migration may therefore
positively impact upon cognitive functioning, potentially
increasing cognitive reserve and delaying the develop-
ment of dementia (Guzmán-Vélez & Tranel, 2015). Given
the significantly higher percentage of immigrants in the
bilingual group, it has been suggested that the beneficial
effect of migration on cognitive reserve may at least par-
tially account for the differences observed between the
monolinguals and bilinguals by Bialystok and colleagues
(Guzmán-Vélez & Tranel, 2015).
Nevertheless, bilingualism has been reported to delay
dementia even after potentially confounding variables
such as immigration and education status have been con-
trolled for (Alladi et al., 2013; Craik et al., 2010). Craik and
colleagues (2010) compared the age of symptom onset
and diagnosis in monolinguals and bilinguals diagnosed
with Probable AD in Canada. Individuals in the bilingual
group were, on average, diagnosed with dementia 4.3
years later than individuals in the monolingual group,
whilst also reporting onset of symptoms 5.1 years later.
Groups did not differ in occupation and cognitive level,
and the monolingual group had received more formal
education, leading the authors to conclude that the dif-
ferences observed between groups could be attributed to
bilingualism.
The results were corroborated by Alladi et al. (2013),
who compared retrospective reports of symptom onset
for all types of dementia in monolinguals and bilinguals
who were all born and raised in India. Significant differ-
ences between groups were observed for several types of
dementia, including AD, frontotemporal dementia and
vascular dementia. Across all dementia types, bilinguals
were, on average, 4.5 years older at the age of onset of
dementia compared to monolinguals. These associations
were found independent of potentially confounding vari-
ables such as education status, occupation, and gender.
However, inconsistencies are present within the literature,
with some studies reporting no significant difference in the
age of symptom onset and the age of diagnosis between
monolinguals and bilinguals (Chertkow et al., 2010; Lawton,
Gasquioine, & Weimer, 2015; Yeung, St. John, Menec, &
Tyas, 2014; Zahodne, Schofield, Farrell, Stern, & Manly,
2014). Zahodne and colleagues (2014) conducted a 23-year
prospective study, following Hispanics living in the USA.
Participants were all fluent in Spanish, and were defined as
bilingual if they reported speaking English “very well”, “well”
or “not well.” They were defined as monolingual if they
reported not speaking English at all. Although bilingual-
ism was associated with initial higher scores on measures of
memory and executive function, no significant differences
were observed in the rate of cognitive decline or the propor-
tion of participants diagnosed with dementia (after control-
ling for potentially confounding variables such as education
level, gender, and age of enrollment). Similar results were
also found by Yeung et al. (2014) and Lawton et al. (2015)
who reported no significant association between bilingual-
ism and the risk of dementia development.

Atkinson: Does Bilingualism Delay the Development of Dementia? 45
Paper Method Relevant ndings
Bialystok, Craik, &
Freedman (2007)
Participants:
132 with probable AD; 52 with other dementias. Recruited in Canada.
Denition of bilingualism:
Bilinguals had “spent the majority of their lives, at least since early adulthood,
regularly using at least two languages”. Monolinguals spoke only English, whilst
bilinguals spoke English and at least one other language (e.g., Polish).
Symptom onset significantly later in bilinguals, even after controlling for
demographics. First appointment at memory clinic was also significantly
later in bilinguals.
Craik, Bialystok, &
Freedman (2010).
Participants:
211 participants with probable AD. Recruited in Canada.
Denition of bilingualism:
Same definition as Bialystok et al. (2007). Monolinguals spoke English. Bilinguals
spoke English and at least one other language (e.g., Yiddish).
Age of symptom onset and diagnosis significantly later in bilinguals.
No significant effect of immigration status. No interaction between immi-
gration status and language group on age of onset of symptoms or age of
diagnosis. This suggests bilingualism delays onset and diagnosis regard-
less of immigration status.
Chertkow et al. (2010). Participants:
632 participants with probable AD. Recruited in Canada.
Denition of bilingualism:
Participants were monolingual (spoke one language), bilingual (spoke two lan-
guages), or multilingual (spoke three or more languages). Definition for bilingual-
ism taken from Bialystok et al. (2007).
Multilinguals had later age of diagnosis and symptom onset than mono-
linguals. No significant differences between bilinguals and monolinguals.
In non-immigrants, English-French bilinguals diagnosed significantly
earlier than monolinguals. However, non-immigrant multilinguals diag-
nosed significantly later than non-immigrant monolinguals.
In immigrants, bilinguals diagnosed significantly later than monolin-
guals.
Gollan, Salmon,
Montoya, &
Galasko (2011).
Participants:
44 bilinguals with probable AD. Recruited in the USA.
Denition of bilingualism:
Participants spoke both Spanish and English. Degree of bilingualism assessed
using the Boston Naming Test (BNT) and self-report.
Overall, higher degree of bilingualism (assessed by BNT) was associated
with a later diagnosis of AD.
Participants separated into low and high education group. Higher degree
of bilingualism only protected against dementia in low education group.
Alladi et al. (2013). Participants:
648 records of patients with dementia recruited in India. All participants were
born and raised in India. Included individuals who were illiterate.
Denition of bilingualism:
Participants were classified as monolingual (spoke one language) or bilingual
(spoke two or more languages). Bilinguals were defined as individuals “with an
ability to meet the communicative demands of the self, and the society in their
normal functioning in two or more languages in their interaction with the other
speakers of any or all of these languages” (Mohanty, 1994). Participants spoke a
variety of languages, including Telugu, Hindi, and English.
Bilinguals developed dementia significantly later than monolinguals,
even after controlling for demographic factors. No additional benefit of
speaking more than two languages.
Illiterate bilinguals developed dementia significantly later than illiterate
monolinguals, suggesting effects are not due to education.
Contd.

Atkinson: Does Bilingualism Delay the Development of Dementia?46
Paper Method Relevant ndings
Zahodne, Schoeld,
Farrell, Stern &
Manly (2014).
Participants:
1,067 Hispanic immigrants recruited in the USA. Records of 228 participants who
developed dementia analysed.
Denition of bilingualism:
Monolinguals spoke Spanish and bilinguals spoke Spanish and English. Partici-
pants were asked how well they speak English. If they answered “not at all”, they
were classed as monolingual. If they answered “not well”, “well” or “very well”, they
were classed as bilingual. A subset of participants completed the English-language
Wide Range Achievement Test Version 3 (WRAT-3) to ensure self-report was valid.
Higher self-reported bilingualism associated with lower chance of
dementia diagnosis, but no significant associations after controlling for
demographic factors.
Similarly, performance on the WRAT-3 did not independently predict
rates of dementia diagnosis after demographic variables controlled for.
Lawton, Gasquoine, &
Weimer (2015).
Participants:
1,789 Hispanic-Americans recruited in the USA. Case records of 55 diagnosed with
probable AD and 26 with vascular dementia examined.
Denition of bilingualism:
Participants spoke Spanish and/or English. To assess language status, participants
were asked “Do you speak Spanish?” and “Do you speak English”. If participants
answered “not at all” or “not very often” about one of the languages, they were
classified as being monolingual. If they answered “very often” or “almost always” to
both, they were classified as being bilingual.
Proportion of monolinguals and bilinguals diagnosed with AD and vascu-
lar dementia did not significantly differ.
Bilinguals diagnosed later than monolinguals, though difference non-
significant. Difference remained non-significant when immigrants and
non-immigrants examined separately.
Woumans et al. (2015). Participants:
134 participants with probable AD recruited in Belgium. All native Belgians.
Denition of bilingualism:
Participants were asked how many languages they had experience using. They
were then asked how proficient they were in each language and how often they
used it. Participants were categorised as being bilingual if they estimated that they
had good proficiency in speaking, reading, writing and listening in two or more
languages, and used them both at least weekly. Monolinguals spoke Dutch or
French. Bilinguals spoke a variety of languages, including Dutch, French, Spanish,
German, and English.
Bilinguals experienced first symptoms significantly later and diagnosed
significantly later, after controlling for demographics.
Yeung, St John,
Menec & Tyas (2014)
Participants:
1,616 older adults recruited in Canada.
Denition of bilingualism:
Self-report. Individuals were classified as a monolingual English speaker, a
bilingual with English as a first language, or a bilingual with English as a second
language. All participants spoke English. Bilinguals spoke English and another
language (e.g., Ukrainian, German, or French).
No significant association between speaking more than one language and
risk of dementia diagnosis.
Table 1: A Summary of Studies which Met the Inclusion Criteria.

Atkinson: Does Bilingualism Delay the Development of Dementia? 47
Further refuting the relationship, Chertkow et al. (2010)
found no significant differences in the age of symptom
onset or dementia diagnosis in monolinguals and bilin-
guals. However, protective effects of multilingualism
were reported, with individuals speaking three or more
languages diagnosed with dementia significantly later
than monolinguals. A significant interaction between
bilingualism and immigration status was also reported.
In immigrants, bilingualism was protective, delaying
dementia diagnosis by almost five years. However, in
non-immigrants, speaking two languages was actually
burdensome, with bilinguals diagnosed with dementia,
on average, 2.6 years earlier than monolinguals.
Thus, based on the aforementioned studies, the rela-
tionship between bilingualism and the development of
dementia is inconclusive. Although some studies have
reported that bilingualism is protective, others have
found no significant differences between groups or even
a detrimental effect. Caution should therefore be taken
when making recommendations on whether bilingualism
delays the onset of dementia.
However, there have been large differences in the
definitions of bilingualism used between studies (e.g.,
language proficiency required and the age of acquisition
of the second language), which may potentially explain
some of the inconsistent findings yielded. Furthermore,
studies have employed different study designs, which may
have also impacted the results found. The next section
will therefore evaluate whether these factors are likely to
be important, and whether they could potentially explain
some of the inconsistent findings reported in this research
area thus far.
Denition of bilingualism used in studies
Language prociency
An important factor which may influence the relationship
between bilingualism and the development of demen-
tia is the level of proficiency in the second language
( Antoniou, Gunasekera, & Wong, 2013; Gollan et al., 2011;
Kavé, Eyal, Shorek, & Cohen-Mansfield, 2008; Kaushans-
kaya & Prior, 2015; Zied et al., 2004). For instance, Zied
and colleagues (2004) reported that balanced bilinguals
(who use both languages proficiently) performed sig-
nificantly better on a Stroop task, measuring executive
function, than unbalanced bilinguals (who were less pro-
ficient in one language). As increased levels of executive
control may mediate the relationship between bilingual-
ism and delayed dementia development, it would follow
that the levels of language proficiency are likely to impact
on whether bilingualism delays the onset of dementia
(Abutalebi, Guidi, et al., 2015; Bialystok, 2011).
The level of proficiency required for participants to be
classified as bilingual has varied substantially between
studies, which may explain some of the inconsistent
findings reported within the research area. Indeed, in
studies which have required participants to be highly pro-
ficient in their second language, bilingualism has been
associated with delayed onset of symptoms and diagno-
sis (Bialystok et al., 2007; Craik et al., 2010; Woumans
et al., 2015). However, in studies which have used more
liberal definitions, non-significant differences have been
reported (Zahodne et al., 2014). Taken together, these
studies suggest that bilingualism may only be protec-
tive if individuals are highly proficient in both languages.
However, this suggestion is speculative and based on a
limited number of studies. Furthermore, some studies
which have used strict proficiency criteria (e.g., Chertkow
et al., 2010) have not found significant difference between
monolingual and bilingual groups, suggesting that lan-
guage proficiency cannot be the only factor responsible
for the inconsistent findings reported.
Age of acquisition of the second language
Another factor proposed to impact upon whether
bilingualism delays onset of dementia is the age of acqui-
sition of the second language (Zahodne et al., 2014).
Given that studies have used differing age of acquisition
criteria, this may potentially explain some of the incon-
sistent findings reported. In many studies reporting that
bilingualism delays the onset and diagnosis of dementia,
participants have been lifelong bilinguals (Bialystok et al.,
2007; Craik et al., 2010). Conversely, in studies where
more liberal definitions of bilingualism have been used,
no significant differences have been reported (Lawton
et al., 2015; Zahodne et al., 2014). In the study conducted
by Zahodne et al. (2014), most participants acquired
their second language during adulthood, whilst in the
study conducted by Lawton et al. (2015), no data on age
of acquisition was collected. Nevertheless, some studies
which have recruited lifelong bilinguals have found no
significant differences between groups (Chertkow et al.,
2010), suggesting that age of acquisition alone cannot
fully account for differences in findings reported between
studies.
Study design
Prospective studies which have followed healthy,
community-dwelling adults for a number of years have
typically found that bilingualism is not associated with
delayed onset or diagnosis of dementia (Lawton et al.,
2015; Yeung et al., 2014; Zahodne et al., 2014). Conversely,
retrospective studies which have investigated age of onset
or diagnosis in individuals already diagnosed with the dis-
ease have typically reported that bilingualism delays the
development of dementia (Alladi et al., 2013; Bialystok
et al., 2007; Craik et al., 2010; Gollan et al., 2011; Wou-
mans et al., 2015). Generally, prospective studies are pre-
ferred to retrospective studies as they are less affected by
potential confounds such as recall bias, where individuals
recall details incorrectly (Guzmán-Vélez & Tranel, 2015).
However, as Bialystok et al. suggested (2007), there is no
reason why bilinguals would be more likely to recall infor-
mation differently to monolinguals. Furthermore, age of
diagnosis was determined by medical records in these
studies (Alladi et al., 2013; Bialystok et al., 2007; Craik
et al., 2010; Gollan et al., 2011; Woumans et al., 2015),
which are unlikely to contain false information. Neverthe-
less, further research is needed to explore why strikingly
different findings have been reported using prospective
and retrospective studies.

Atkinson: Does Bilingualism Delay the Development of Dementia?48
Conclusions and Recommendations for Further
Research
In conclusion, research investigating the relationship
between bilingualism and the onset of dementia has
yielded inconsistent findings. Some studies have suggested
that bilingualism protects against dementia, whilst others
have suggested that there is likely to be no benefit or
even a detrimental effect of speaking two or more lan-
guages. To some extent, these inconsistent findings can
be resolved by taking into account the sample of partici-
pants recruited and the study design used. Retrospective
studies which have used a strict definition of bilingualism
have generally found significant results, whilst prospec-
tive studies using more liberal definitions have not. Based
on the available evidence, it can therefore be concluded
that lifelong bilingualism, where both languages are used
frequently, may be protective against dementia. Delays
in the development of dementia are unlikely to occur if
participants become bilingual during adulthood or infre-
quently use their second language. As such, it should not
be recommended that individuals learn a second language
as a method for delaying or preventing the development
of dementia.
The inconsistent findings between studies could not,
however, be fully attributed to differences in the defini-
tions of bilingualism used, as some studies which have
employed strict criteria have found no protective effect of
bilingualism (Chertkow et al., 2010). Additional research
is therefore required to investigate whether bilingualism
significantly delays the development of dementia. This
research should control for potentially confounding fac-
tors such as demographic variables, whilst also carefully
controlling for language factors that may affect the rela-
tionship (such as age of acquisition of the second language
and language proficiency). Where possible, this research
should use prospective study designs, which are gener-
ally preferred to retrospective designs ( Guzmán-Vélez &
Tranel, 2015).
To conclude, lifelong bilingualism where individuals fre-
quently use both languages appears to significantly delay
dementia, though benefits are unlikely to emerge if indi-
viduals become bilingual later in life or use their second
language infrequently.
Acknowledgements
The author would like to thank Dr Jelena Havelka for
useful discussion.
Competing Interests
The author declares that they have no competing interests.
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Atkinson: Does Bilingualism Delay the Development of Dementia?50
How to cite this article: Atkinson, A. L. (2016). Does Bilingualism Delay the Development of Dementia?
Journal of
European Psychology Students
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Published: 31 August 2016
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