Age and Ageing 2016; 45: 523–528
doi: 10.1093/ageing/afw049
Published electronically 7 April 2016
© The Author 2016. Published by Oxford University Press on behalf of the British Geriatrics Society.
All rights reserved. For Permissions, please email: [email protected]
Education as protector against dementia,
but what exactly do we mean by education?
FRANCISCA S. THEN1,2, TOBIAS LUCK1,2, MATTHIAS C. ANGERMEYER3,4, STEFFI G. RIEDEL-HELLER1
1
Institute of Social Medicine, Occupational Health and Public Health, University of Leipzig, Leipzig, Germany
LIFE—Leipzig Research Center for Civilization Diseases, University of Leipzig, Leipzig, UK
3
Center for Public Mental Health, Gösing a.W., Austria
4
Department of Public Health and Clinical and Molecular Medicine, University of Cagliary, Cagliary, Italy
2
Address correspondence to: F. S. Then. Tel: (+49) 341 971 5475; Fax: (+49) 341 972 4569. Email: francisca.then@medizin.
uni-leipzig.de
Abstract
Objectives: even though a great number of research studies have shown that high education has protective effects against dementia, some studies did not observe such a significant effect. In that respect, the aim of our study was to investigate and
compare various operationalisation approaches of education and how they impact dementia risk within one sample.
Methods: data were derived from the Leipzig longitudinal study of the aged (LEILA75+). Individuals aged 75 and older
underwent six cognitive assessments at an interval of 1.5 years and a final follow-up 15 years after the baseline assessment.
We operationalised education according to different approaches used in previous studies and analysed the impact on dementia
incidence via multivariate cox regression modelling.
Results: the results showed that whether education is identified as significant protector against dementia strongly depends on
the operationalisation of education. Whereas the pure number of years of education showed statistically significant protective
effects on dementia risk, other more complex categorical classification approaches did not. Moreover, completing >10 years of
education or a tertiary level seems to be an important threshold to significantly reduce dementia risk.
Conclusion: findings suggest a protective effect of more years of education on a lower dementia risk with a particular critical
threshold of completing >10 years of education. Further, the findings highlight that, when examining risks and protective
factors of dementia, a careful consideration of the underlying definitions and operationalisation approaches is required.
Keywords: cognitive reserve, dementia, education, longitudinal cohort study, older people
Introduction
One aspect strongly related to better health is education. Higher
education not only encourages healthier behaviours but also
promotes less risky life contexts, lower costs of dependence
and lost earnings, the use of preventative services, fosters personal, family and community well-being [1]. Education has also
shown to be significant factor regarding the risk to develop dementia. Higher education seems to decrease the risk to develop
dementia [2] and helps to sustain a good level of cognitive functioning for a longer lifetime period [3]. This is in particular of
high relevance as dementia is a terminal disease characterised
by a long degenerative progression with severe impairments in
daily functioning [4], which—due to the demographic changes
with increasing numbers of individuals affected by dementia—
is confronting healthcare systems and the society with major
challenges [5]. Current theories assume that protective effects
of higher education on the risk to develop dementia may not
only be brought about by a healthier lifestyle pattern but also by
a so-called ‘cognitive reserve’. A ‘cognitive reserve’ is the ability
to keep up a good cognitive performance despite brain pathology [6]. It is assumed that cognitive activity, such as education,
shapes neural activity and brain measures and in this way builds
up a cognitive reserve [7]. Accordingly, a higher level of education might build up a better cognitive reserve which then—
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together with an overall healthier behaviour—reduces the risk
to develop dementia.
However, when investigating the effect of education on
the risk to develop dementia, it is important to consider
how education is operationalised. Education can be measured,
for example, solely in years or also in certain levels of educational degrees attained. It is important to know how the operationalisation of education is influencing the effects observed
on the risk to develop dementia to gain a better understanding
of the processes linking education with dementia. In this
study, we therefore compared various operationalisation
approaches of education and analysed the impact on dementia
incidence via multivariate cox regression modelling in data
from a population-based study.
Methods
Study design
Data were derived from the Leipzig Longitudinal Study of the
Aged (LEILA75+), a population-based study on dementia and
cognitive impairment. The study design has been described in
detail by Riedel-Heller et al. [8]. Systematic random sampling by
age-ordered list from the local registry office identified 1,500
community-dwelling individuals aged 75 and older in the city
area of Leipzig, Germany. Additionally, 192 individuals were
recruited from nursing homes in the sampling area. At baseline
(1997–98), a total of 1,692 individuals were invited to participate in the study. Of these individuals, 242 (14.2%) refused to
participate, 113 (6.7%) had only proxy interviews, 57 (3.4%)
died and 15 (0.9%) could not be located. Participants and nonparticipants did not differ significantly regarding gender, age or
marital status [8]. The total follow-up period consisted of 15
years, during which the first through the fifth assessments were
conducted at 1.5-year intervals, and a final assessment was realised after 15 years. Two hundred and thirty-four participants
were lost due to follow-up (n = 220 had dementia at baseline,
n = 14 had incomplete educational information). For purpose
of analyses, 83 participants had to be excluded due to incomplete follow-up data, n = 7 due to incomplete covariate information and n = 3 were special cases. The final sample used for
analysis comprised a total of 938 individuals. The details of the
flow of participants are illustrated in Supplementary data,
Appendix, available in Age and Ageing online.
Standard protocol approval and patient consents
All study participants provided written informed consent
prior to study participation. The study was approved by the
ethics committee of the University of Leipzig.
Data collection and assessments
At baseline and subsequent follow-up waves, trained psychologists and physicians visited the participants in their home environment. A standardised interview provided information on the
participants’ socio-demographical status, medical conditions
524
and other characteristics. The main assessment instrument of
cognitive functioning was the Structured Interview for diagnosis of Dementia of the Alzheimer type, Multi-infarct dementia
and dementias of other aetiology according to ICD-10 and
DSM-III-R (SIDAM; [9]). The SIDAM includes (i) a cognitive
test section, (ii) a third-party rating of psychosocial impairment,
(iii) a section for clinical judgment and (iv) a system of clinical
diagnostic classification. In consensus conferences, physicians
and psychologists have diagnosed dementia based on the standardised diagnostic algorithm of the DSM-IV criteria for dementia which are implemented in the SIDAM, the clinical
evaluation comprised judgments on the presence or absence of
impairment in memory and other cognitive domains (based on
the participant’s results in the cognitive test battery), the presence or absence of significant impairment in social or occupational functioning (caused by the cognitive deficits, representing
a significant decline from a previous level of functioning), as
well as the presence or absence of delirium. Based on these
judgments, a clinical diagnosis of dementia was made. If it was
not possible to administer the SIDAM (e.g. because of death or
severe weakness of the participants), a comprehensive structured proxy interview including the Clinical Dementia Rating
scale (CDR [10]) was offered.
The information on education, as indicated at baseline assessment, was operationalised according to different approaches used
in previous studies [11–13]. Additionally to years of education,
we classified the participants’ educational level as (i) having completed compulsory education, (ii) having completed a primary,
secondary (school diploma such as ‘Volksschule’, ‘Mittelschule’,
‘Hauptschule’ or higher), tertiary (educational degree higher than
secondary such as vocational school certificate or advanced education), and university-level degree (university-level degree equivalent to 5 years of university education), (iii) the International
Standard Classification of Education (ISCED [14]) and (iv) the
Comparative Analysis of the Development and Structure of
Educational Systems (CASMIN [15]).
Statistical analyses
All statistical analyses employed an alpha level for statistical
significance of 0.05 (two-tailed) and were performed using
IBM SPSS Statistics (version 20 [16]).
Comparison of the socio-demographic and educational
characteristics with respect to dementia incidence was
accomplished using the Mann–Whitney U test or the χ 2 test
after Pearson.
The impact of education on the incidence of dementia was
analysed via multivariate Cox regression modelling. In a first
step, we analysed only the impact of the respective educational
parameter on dementia incidence (Model 1). In a second step,
we adjusted the analyses for age (continuous) and gender
(male/female) (Model 2). In a third step, we additionally
adjusted the analyses for marital status (married/single/
divorced/widowed), living situation (alone/with others/nursing
home), diabetes mellitus (yes/no), heart attack (yes/no), stroke
(yes/no) and history of depression (yes/no) (Model 3).
Education as protector against dementia
Table 1. Baseline socio-demographic and educational
characteristics of individuals who developed dementia
throughout the study and those who stays dementia free
(n = 983)
Dementia free
N (%)
Incident dementia
N (%)
P*
216 (87.8)
533 (77.0)
30 (12.2)
159 (23.0)
<0.001
676 (79.4)
73 (83.9)
175 (20.6)
14 (16.1)
0.322
710 (80.9)
39 (65.0)
168 (19.1)
21 (35.0)
0.003
678 (79.0)
71 (88.8)
180 (21.0)
9 (11.2)
0.038
585 (80.9)
164 (76.3)
138 (19.1)
51 (23.7)
0.137
276 (86.5)
425 (80.2)
48 (53.9)
43 (13.5)
105 (19.8)
41 (46.1)
<0.001
231 (89.2)
65 (81.2)
65 (78.3)
388 (79.9)
28 (10.8)
15 (18.8)
18 (21.7)
128 (24.8)
<0.001
130 (71.0)
619 (82.0)
53 (29.0)
136 (18.0)
0.001
143 (70.4)
606 (82.4)
60 (29.6)
129 (17.6)
<0.001
492 (77.6)
257 (84.5)
142 (22.4)
47 (15.5)
0.013
130 (71.0)
362 (80.3)
257 (84.5)
53 (29.0)
89 (19.7)
47 (15.5)
0.001
477 (78.2)
172 (81.5)
100 (85.5)
133 (21.8)
39 (18.5)
17 (14.5)
0.157
650 (79.1)
99 (85.3)
172 (20.9)
17 (14.7)
0.115
145 (70.0)
604 (82.6)
62 (30.0)
127 (17.4)
<0.001
130 (71.0)
362 (80.3)
257 (84.5)
53 (29.0)
89 (19.7)
47 (15.5)
0.001
89 (66.9)
414 (80.5)
136 (85.0)
47 (79.7)
56 (86.2)
7 (100)
44 (33.1)
100 (19.5)
24 (15.0)
12 (20.3)
9 (13.8)
0 (0.0)
0.001
........................................
Gender
Male
Female
Depression
No
Yes
Stroke
No
Yes
Heart attack
No
Yes
Diabetes
No
Yes
Living situation
With someone
Alone
Nursing home
Marital status
Married
Single
Divorced
Widowed
Education: 9 years
≤9 years
>9 years
Education: 10 yearsa
≤10 years
>10 years
Education: 12 years
≤12 years
>12 years
Education: categorised by years
≤9 years
10–12 years
>12 years
Education: CASMIN
Low
Middle
High
Education: University
No
Yes
Education: Tertiary
No
Yes
Education: Compulsory
Only compulsory
>Compulsory up to 12 years
<12 years
Education: ISCED 2011
2
3
4
5
7
8
Table 1. Continued
Dementia free
N (%)
Incident dementia
N (%)
P*
N = 749
Mean (SD)
80.9 (4.6)
12.1 (1.8)
N = 189
Mean (SD)
84.0 (4.8)
11.4 (1.8)
P**
........................................
Age
Years of education
<0.001
<0.001
CASMIN, Comparative Analysis of the Development and Structure of
Educational Systems ((16)); ISCED, International Standard Classification of
Education (UNESCO 2011); n, number of participants; P, level of significance;
SD, standard deviation.
a
As there were no participants with exactly 11 years of education, we skipped the
category </> 11 years of education.
*χ 2 test after Pearson.
**Mann–Whitney U test.
Study funding
This publication is supported by a junior research grant by the
Medical Faculty of the University of Leipzig (No. 971000-084)
and LIFE—Leipzig Research Center for Civilization Diseases,
Universität Leipzig, which was funded by means of the
European Social Fund and the Free State of Saxony. The
LEILA75+ study was funded by the Interdisciplinary Centre
for Clinical Research of the University of Leipzig (IZKF,
Project C07).
Results
The participants’ mean age at baseline was 81.5 years (SD 4.8).
The average number of years of education completed was 11.9
years (SD 1.8). One hundred and eighty-nine participants
(20.1%) developed dementia during the subsequent 15-year
follow-up period. The participants’ characteristics with respect
to incident dementia are shown in Table 1. Female gender,
higher age, being widowed or divorced, living in a nursing
home, having had a stroke and overall a lower educational level
were significantly associated with incident dementia.
The results showed differently effects of education on incident dementia, depending on the operationalisation of education (see Table 2). Whereas the pure number of years of
education showed statistically significant protective effects on
dementia risk, other more complex classification approaches
did not (ISCED, Compulsory Education, CASMIN). In particular, besides the pure number of years of education, only
‘having completed >10 years of education’ or a ‘tertiary level
of education’ were significantly associated with a lower dementia risk in the fully adjusted models. The effect sizes of ‘having
completed >10 years of education’ or a ‘tertiary level of education’ were similar (see Table 2)—also displayed graphically by
the hazard functions on dementia incidence in Figure 1.
Discussion
Continued
In this study, we investigated how the operationalisation of
education may affect the size and the significance level of the
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F. S. Then et al.
Table 2. Hazard ratios of Cox regression analyses on the impact of education on incident dementia in individuals aged 75 and
older (n = 938)
Educationa
Model 1
Model 2
Model 3
Univariate
Adj. age, gender
Adj. age, gender, marital status,
living situation, diabetes, heart
attack, stroke, history of
depression
HR (95% CI)
P
HR (95% CI)
P
HR (95% CI)
P
0.829 (0.766–0.897)
0.540 (0.393–0.742)
0.517 (0.380–0.702)
0.622 (0.447–0.866)
0.783 (0.681–0.900)
[no cases for primary level]
0.499 (0.368–0.676)
0.629 (0.382–1.036)
<0.001
<0.001
<0.001
0.005
0.001
0.887 (0.814–0.966)
0.684 (0.491–0.953)
0.642 (0.466–0.886)
0.792 (0.566–1.108)
0.891 (0.770–1.030)
0.006
0.025
0.007
0.173
0.119
0.905 (0.830–0.988)
0.716 (0.513–1.000)
0.683 (0.494–0.945)
0.860 (0.608–1.216)
0.901 (0.777–1.045)
0.025
0.050
0.021
0.393
0.169
<0.001
0.068
0.623 (0.452–0.857)
0.960 (0.572–1.611)
0.004
0.876
0.658 (0.477–0.908)
1.062 (0.626–1.803)
0.011
0.823
[no cases]
Ref
0.520 (0.380–0.710)
0.395 (0.231–0.676)
<0.001
<0.001
0.001
[no cases]
Ref
0.620 (0.449–0.856)
0.655 (0.367–1.167)
0.015
0.004
0.151
[no cases]
Ref
0.651 (0.471–0.902)
0.749 (0.415–1.352)
0.035
0.010
0.337
Ref
0.609 (0.434–0.856)
0.444 (0.300–0.658)
<0.001
0.004
<0.001
Ref
0.715 (0.504–1.015)
0.626 (0.415–0.944)
0.063
0.060
0.025
Ref
0.728 (0.511–1.037)
0.692 (0.455–1.050)
0.142
0.079
0.084
Ref
0.609 (0.434–0.856)
0.444 (0.300–0.658)
<0.001
0.004
<0.001
Ref
0.715 (0.504–1.015)
0.626 (0.415–0.944)
0.063
0.060
0.025
Ref
0.728 (0.511–1.037)
0.692 (0.455–1.050)
0.142
0.079
0.084
Ref
0.799 (0.559–1.142)
0.586 (0.353–0.971)
0.077
0.219
0.038
Ref
0.892 (0.623–1.277)
0.917 (0.542–1.551)
0.802
0.532
0.742
Ref
0.945 (0.655–1.0365)
1.031 (0.602–1.767)
0.943
0.764
0.912
....................................................................................
Scale measures
Years
≤9 years
≤10 years
≤12 years
ISCED
Secondary
Tertiary
University
Category measures
Level of education
Primary
Secondary
Tertiary
University
Compulsory education
Only compulsory
> Compulsory up to 12 years
<12 years
Categorised years of education
<10 years
10–12 years
>12 years
CASMIN classification
Low
Middle
High
Adj., adjusted for; CASMIN, Comparative Analysis of the Development and Structure of Educational Systems [14]; CI, confidence interval; HR, hazard ratio; ISCED,
International Standard Classification of Education (UNESCO 2011); Ref, reference group; P, level of significance; SD, standard deviation. Bold, the level of
significance level was <0.05.
a
As there were no participants with exactly 11 years of education, we skipped the category </> 11 years of education.
Figure 1. Risk of dementia by educational level as indicated by multivariate Cox regression modelling adjusted for age, gender, marital
status, living situation, diabetes, heart attack, stroke and history of depression. (A) Operationalising education by dark line, 10 years or
less education; light-colored line, more than 10 years of education. (B) Operationalising education by having dark line, did not complete
a tertiary level of education; light-colored line, completed tertiary level of education.
526
Education as protector against dementia
effect of education on dementia incidence. Our findings
suggest that education expressed in the number of years has
a significant protective effect against dementia incidence.
Specifically, the findings point out that completing >10 years
of education or a tertiary level of education seems to be an
important threshold to significantly reduce dementia risk.
More complex operationalisation approaches of education,
however, indicated no significant effect on dementia incidence. The findings thus emphasise that a careful consideration of the underlying definitions and operationalisation
approaches is required when examining risks and protective
factors of dementia. Coherence of definitions and operationalisation is not only essential for reaching corresponding
consensus research results, it is also necessary to be able to
gain a better understanding of the processes linking education with dementia.
Our findings are in conformity with previous studies that
demonstrated a significant association between a higher
number of years of education and a decreased dementia risk
[17, 18]; an association that has also been observed in a
meta-analysis [19]. The number of years of education attained
may also be related to childhood mental abilities. However, evidence indicates that even though school performance (e.g.
grades) is important regarding dementia risk, the number of
years of education additionally lower dementia risk [20, 21].
Indeed, studies that used educational operationalisation—like illiteracy or very few years of education—persistently reported
strong effects, whereas the most frequently chosen operationalisation of education in other studies—a cut-off at 7 or 8 years of
education—rendered rather inconsistent associations [11, 17]. It
is possible that just a few years of education could make a substantial difference regarding dementia risk, while the difference
in effect size between attaining 6 or 8 years of education probably is not that distinct.
Our findings point out another important point for
understanding how education may be linked to dementia:
Complex classification of education was rather not significant
with respect to dementia incidence. The complex classifications of education (e.g. ISCED, CASMIN) focus on learning
objectives, occupational qualifications and resources invested
[14]. One way to interpret the findings is that factors like
learning objectives or qualifications do not explain the effect
that education has on dementia risk. Moreover, these factors
are culture specific, and the results may vary depending on
the setting of the study. As our results implicate, it seems to
be rather the duration of mental training—i.e. years of education—that is the factor lowering dementia risk. This finding
relates well to the cognitive reserve theory. According to the
cognitive reserve theory, mental activities during the lifecourse build up a cognitive reserve which makes the brain resistant to pathological damages like those due to dementia
[7]. Based on the here presented findings, the duration of
mental activities—i.e. education—plays an important role in
building up the cognitive reserve and in this way lowers dementia risk. Yet, even when this is the case, there still remains
the question if the effect of education is the same for each
year of education or whether there are threshold or ceiling
effects or whether there may be critical ‘age windows’. Our
findings suggest that there could be a threshold at 10 years of
education. However, further investigations are necessary to
validate pathways from education to dementia risk.
Education is not only a resource against dementia; it is also
associated with better health in general. Studies have shown
that a higher level of education is associated with lower mortality, heart disease, diabetes, hypertension, anxiety and others
[22]. Even though factors such as family background, higher
income, better jobs or health insurance partially explain this
effect, they do not fully explain the impact of higher education
on better health [22–24]. There are attempts to explain why
higher educated individuals may have better health referring to
cognitive skills. Higher education is considered to also
improve health-related knowledge and problem-solving skills
[23] as well as access to information and critical thinking [22].
From this perspective, higher education provides a comprehensive set of cognitive training: On one hand, education
builds up a cognitive reserve that improves the level of cognitive functioning and makes it more resistant to cognitive
decline, and on the other hand, it promotes a lifestyle pattern
that leads to a better health which may then also lower dementia risk. The exact details as well as whether and what type of
moderation effects are at work between education, health, cognitive skills and lifestyle will have to be investigated in further
studies.
Our study is not without limitations. First, the sample investigated comprised mainly women and only few males.
Moreover, all the individuals were healthy enough to undergo
cognitive testing at an age of 75 years and older. Second, due to
the cultural background of our sample, education and access to
health system were not interconnected. Conducting this analysis
in countries where education is a key to get access to health services, the effect of education on dementia risk may be much
stronger and different operationalisation approaches may show
up significant. Moreover, the cultural setting could also have
influenced the effect size, in particular that of the complex classifications of education. For our sample, primary education was
compulsory and tertiary education was almost always free (in
fact, the government motivated worker’s children to attend universities) [25, 26]. Third, the small number of cases in the higher
educated groups potentially underestimated the true effect.
Finally, even though we controlled for a great number of confounders, other unknown factors may affect the associations.
Conclusions
Our longitudinal observations emphasise, on one hand, protective effects of more years of education against dementia
and, on the other hand, the importance of considering definitions and operationalisation in dementia research. Only by
being aware of the applied definitions and operationalisation,
it will be possible to gain a better understanding of the processes that influence dementia risk. Particularly, as dementia
is a terminal disease with a long degenerative progression
which imposes enormous societal challenges, it is extremely
527
F. S. Then et al.
important to generate a comprehensive profile of risk factors
and their effect sizes. Further research should evaluate what
level of education would be optimal as major public health
goal, especially for developing countries, to alleviate health
care systems and the society from some of the dementia
burden.
Key points
• The impact of education on dementia risk differed depending on the operationalisation approach.
• More years of education seem to lower dementia risk with a
critical threshold of completing >10 years of education.
• Complex classification of education was not significant
with respect to dementia incidence.
• Understanding how education is linked to dementia risk
requires a careful consideration of the underlying definitions.
9.
10.
11.
12.
13.
14.
15.
Supplementary data
Supplementary data mentioned in the text are available to
subscribers in Age and Ageing online.
16.
Conflicts of interest
17.
None declared.
18.
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Received 16 December 2015; accepted in revised form
18 February 2016