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Titre: New Insights into the Dementia Epidemic

Auteur: Larson Eric B., Yaffe Kristine, Langa Kenneth M.

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PE R S PE C T IV E

Pharmacogenetics and Coumarin Dosing

quiring hospitalization in the
pharmacogenetic group, whereas
three such events occurred in the
control group. These trends, which
are consistent across studies, suggest that uncommon but clinically meaningful outcomes should be
considered in addition to intermediate end points (e.g., percentage of time in the therapeutic
range) in a totality-of-evidence approach to assessing the usefulness
of pharmacogenetic approaches.
The public’s expectations for
pharmacogenetics may arguably
be declining. Logistic and evidentiary challenges have converged to create disillusionment
regarding the relevance of pharmacogenetics. Many observers
have called for randomized, controlled trials to address the
translation lag. Methodologic
rigor is critical in evidence assessment, and it is equally im-

portant to design experiments to
definitively clarify issues of public health relevance. Randomization, in and of itself, does not
accomplish this end. Rather, the
choice of control, the treatment
setting, characteristics of the population tested, the analytic approach, and end-point definition
are likely to be the key considerations that determine the public
health relevance of pharmacogenetic trials in the future. Future
trials should use various methods
to assess the clinical usefulness
of pharmacogenetic interventions;
these may include designs focused
on assessing efficacy (emphasis on
internal validity), effectiveness (em
phasis on generalizability), and
implementation effectiveness (emphasis on adoption and uptake).2
These approaches are not mutually
exclusive and, if combined, may
expedite assessment of the effects

of pharmacogenetic interventions
on patients, providers, and health
systems.3,4
Disclosure forms provided by the authors
are available with the full text of this article
at NEJM.org.
From the Center for Drug Evaluation and
Research, Food and Drug Administration,
Silver Spring, MD.
1. Coumadin (warfarin sodium) (package
insert). Princeton, NJ: Bristol-Myers Squibb
(http://www.accessdata.fda.gov/drugsatfda
_docs/label/2011/009218s107lbl.pdf).
2. Flay BR. Efficacy and effectiveness trials
(and other phases of research) in the development of health promotion programs. Prev
Med 1986;15:451-74.
3. Glasgow RE, Lichtenstein E, Marcus AC.
Why don’t we see more translation of health
promotion research to practice? Rethinking
the efficacy-to-effectiveness transition. Am J
Public Health 2003;93:1261-7.
4. Curran GM, Bauer M, Mittman B, Pyne
JM, Stetler C. Effectiveness-implementation
hybrid designs: combining elements of clinical effectiveness and implementation research to enhance public health impact. Med
Care 2012;50:217-26.
DOI: 10.1056/NEJMp1314529
Copyright © 2013 Massachusetts Medical Society.

New Insights into the Dementia Epidemic
Eric B. Larson, M.D., M.P.H., Kristine Yaffe, M.D., and Kenneth M. Langa, M.D., Ph.D.

D

escribed in the early 1980s
as “The Silent Epidemic,”
dementia in the elderly will soon
become a clarion call for public
health experts worldwide. The
epidemic is largely explained by
the prevalence of dementia in persons 80 years of age or older. In
most countries around the world,
especially wealthy ones, this “old
old” population will continue to
grow, and since it accounts for
the largest proportion of dementia cases, the dementia epidemic
will grow worldwide. The combined effects of longer lives and
the dramatic bulge of baby
boomers reaching old age will
magnify the epidemic in future
decades.
Although demographics will
drive an increase in the number

of dementia cases, recent reports
— generally based on population-based community studies or
survey data — point to declining
age-specific prevalence or incidence rates among people born
later in the first half of the 20th
century (see table). We believe
these reports are intriguing and
inform our understanding of potentially modifiable factors that
contribute to the epidemic of this
common and often tragic condition. Knowing about contributing
factors is especially important
for the study and development of
prevention strategies, and prevention is often the key to better
control of epidemics, including
epidemics of chronic diseases.
In 2005, Manton and colleagues
published an intriguing article en-

titled “Declining Prevalence of
Dementia in the U.S. Elderly
Population.”1 On the basis of their
analysis of 17 years of national
long-term care surveys, conducted
from 1982 through 1999, they reported a decrease in dementia
prevalence from 5.7% to 2.9% during that period. They pointed to
higher levels of education, a reduction in stroke rates, and other
factors as possible contributors to
the decrease.
This report was followed by an
analysis of the U.S. Health and
Retirement Study, an ongoing population-based, longitudinal survey
of a nationally representative sample of adults 51 years of age or
older.2 In 1993, 12.2% of surveyed adults 70 years of age or
older had cognitive impairment,

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PERS PE C T IV E

New Insights into the Dementia Epidemic

Selected Recent Studies of the Dementia Epidemic.
Study

Outcome

Data Source

Prevalence of se National long-term care
Manton et al.
vere cognitive
survey interviews,
(United States)1
impairment
1982–1999
Prevalence of
Langa et al.
cognitive
(United States)2
impairment

Key Findings

Factors

Decline in dementia prevalence among Higher educational level,
people ≥65 yr of age (5.7% to 2.9%)
decline in stroke
incidence

Ongoing population-based Prevalence of cognitive impairment
survey of people ≥51 yr
among people ≥70 yr of age (12.2%
of age
in 1993 vs. 8.7% in 2002)

Higher educational level;
combination of medical,
lifestyle, demographic,
and social factors

Schrijvers et al.
(Rotterdam)3

Incidence of
dementia

Population-based cohort
≥55 yr of age in 1990,
extended in 2000

Incidence rate ratios (6.56 per 1000
person-yr in 1990 vs. 4.92 per 1000
person-yr in 2000)

Higher educational level, reduction in vascular risk,
decline in stroke incidence

Qiu et al.
(Stockholm)4

Prevalence of
DSM-III-R
dementia*

Cross-sectional survey of
people ≥75 yr of age,
1987–1989 and 2001–
2004

Age- and sex-standardized dementia
prevalence (17.5% in 1987–1989 vs.
17.9% in 2001–2004); lower hazard
ratio for death in later cohort sug
gests decreased dementia incidence

Favorable changes in risk
factors, especially
vascular risk; healthier
lifestyles

Matthews et al.
(England)5†

Prevalence of
dementia in
3 regions

Survey interviews of people Dementia prevalence (8.3%
≥65 yr of age, 1989–
in CFAS I vs. 6.5% in CFAS II)
1994 (in CFAS I) and
2008–2011 (in CFAS II)

Higher educational level,
better prevention of
vascular disease

* In the study by Qiu et al., dementia was diagnosed according to the criteria provided in the Diagnostic and Statistical Manual of Mental
Disorders, third edition, revised (DSM-III-R).
† CFAS denotes Cognitive Function and Ageing Study.

as compared with 8.7% in 2002.
Education was protective against
cognitive impairment, and the results suggested that “overall, the
combined impact of recent trends
in medical, lifestyle, demographic,
and social factors has been positive for the cognitive health of
older Americans.”2
Three recent studies of Euro
pean populations support the optimistic view that dementia risk
may be decreasing among older
adults.3-5 The Rotterdam Study,3
in which researchers studied a
cohort of inhabitants 55 years of
age or older in 1990 and then
studied a subcohort again in
2000, showed lower incidence
rates in the 2000 subcohort; although the differences were not
statistically significant, they were
consistent across many groups.
Statistical power was limited because the subcohort was smaller
and had shorter follow-up than
the overall cohort. Most intrigu
ing was the observation of larger
brain volumes and less extensive
2276

cerebral small-vessel disease on
magnetic resonance imaging in
persons born later. The authors
compared scans of persons without dementia in 1995–1996 with
scans obtained in 2005–2006 and
reported that the differences supported their “finding of declining
dementia incidence.” They hypothesized that these changes were attributable to secular changes in
education, population-level reductions in vascular risk factors, and
an overall reduction in stroke incidence.
We also have recent reports
from Sweden and England.4,5
The Swedish study entailed two
cross-sectional surveys of people
75 years of age or older who
were living in central Stockholm
in 1987–1989 and in 2001–2004,
with analysis of death certificates
to determine their survival status
in December 1994 and June 2008,
respectively. The age- and sexstandardized prevalence of dementia in the two surveys was
similar: 17.5% in 1987–1989 and

17.9% in 2001–2004. However,
because the hazard ratio for
death was lower in the later cohort, including among persons
with dementia, the authors argue
that the incidence of dementia
may have decreased during the
period between surveys, probably
owing to favorable changes in
multiple risk and protective factors
— notably, vascular risk factors
and healthier lifestyles, especially
among older people.
The most recent report compares the Cognitive Function and
Ageing Study (CFAS) I and II,5
two surveys of populations 65
years of age or older — CFAS I,
conducted between 1989 and
1994, and CFAS II, conducted between 2008 and 2011, each with
a sample size of more than 7500.
The authors report standardized
dementia prevalence rates of 8.3%
in CFAS I, as compared with 6.5%
in CFAS II. They conclude that
populations born later have a
lower risk of dementia than those
born earlier, probably because of

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PE R S PE C T IV E

New Insights into the Dementia Epidemic

higher education levels and better prevention of vascular disease, even in the face of countervailing factors such as diabetes
and survival after stroke, which
could increase age-specific dementia prevalence.
We study epidemics not just
as an exercise in counting but especially to learn ways to reduce
diseases’ effects on individuals
and populations. After early tentative, suggestive findings of decreasing rates over time, the consistency of these recent findings
is encouraging and noteworthy,
especially since the projected
growth of the population older
than 75 years guarantees a growing epidemic of dementia.
Eventually, we will have results
of studies conducted over longer
periods with presumably more
definitive findings. But for now,
the evidence supports the theory
that better education and greater
economic well-being enhance life
expectancy and reduce the risk of
late-life dementias in people who
survive to old age. The results
also suggest that controlling vascular and other risk factors during midlife and early old age has
unexpected benefits. That is, individual risk-factor control may provide substantial public health
benefits if it leads to lower rates
of late-life dementias. Just as control of vascular risk factors has
had measurable effects
An audio interview
with Dr. Larson
on public health through
may be heard at NEJM.org
reduced rates of stroke
and myocardial infarction, the
recent English study concluded
that estimates of national dementia prevalence based on CFAS I
needed to be revised downward
by 24% on the basis of the ageand sex-specific prevalence rates
in 2011 found in CFAS II.5
Recent attention and resources
have been directed at identifying
preclinical dementia, especially

Alzheimer’s disease, and at preventive-drug trials that enroll the
very few persons who are at extremely high risk for the disease,
such as those with dominantly
inherited mutations (which account for <1% of cases). Although
this strategy is important for the
development of effective treatments, the recent studies highlighted above illustrate the potential for deriving widespread
public health benefits from such
lifestyle interventions as improving educational opportunities in
both early and later life, reducing
vascular risk factors, and promoting greater physical activity.
These studies also remind us that
dementia is a syndrome — a
complex of symptoms with multiple causes — making it similar
to most late-life chronic diseases.
In fact, population-based studies
have convincingly demonstrated
that the vast majority of dementia
cases, especially those occurring
very late in life, tend to involve a
mixture of Alzheimer’s disease,
vascular disease, and other degenerative factors.
Research on preventing latelife dementias should explore
ways of reducing risk factors at
both the societal and the personal levels. We don’t know the extent to which better risk-factor
control can reduce dementia rates.
However, a potentially ominous
trend that could lead to a reversal of the decrease in risk is the
growing prevalence of obesity
and diabetes among middle-aged
and younger people. Other factors
to consider in the United States
and other countries with increasingly racially and ethnically diverse
older populations are changes
seen in some groups of secondand third-generation Americans
that might drive increased risk
for vascular disease. Improvement
in life expectancy will certainly

lead to a net increase in the
number of older people who have
dementia late in their lives. This
fact alone, plus population trends,
justifies the value of learning
more about lifestyle and risk factors that affect dementia rates.
Given recent reports of trends in
dementia incidence and prevalence, we believe that research to
uncover influences on these
trends has great promise.
The views expressed in this article are
those of the authors and do not necessarily
reflect the position or policy of the
Department of Veterans Affairs or the U.S.
government.
Disclosure forms provided by the authors
are available with the full text of this article
at NEJM.org.
From the Group Health Research Institute
and the Departments of Medicine and
Health Services, University of Washington
— both in Seattle (E.B.L.); the Departments
of Psychiatry, Neurology, and Epidemiology
and Biostatistics, University of California,
San Francisco, and the San Francisco Veterans Affairs (VA) Medical Center — both in
San Francisco (K.Y.); and the Division of
General Medicine, VA Ann Arbor Center for
Clinical Management Research, and the Institute for Social Research, Institute of Gerontology, and Institute for Healthcare Policy and Innovation, University of Michigan
— all in Ann Arbor (K.M.L.).
This article was published on November 27,
2013, at NEJM.org.
1. Manton KC, Gu XL, Ukraintseva SV. Declining prevalence of dementia in the U.S.
elderly population. Adv Gerontol 2005;16:
30-7.
2. Langa KM, Larson EB, Karlawish JH, et al.
Trends in the prevalence and mortality of
cognitive impairment in the United States:
is there evidence of a compression of cognitive morbidity? Alzheimers Dement 2008;4:
134-44.
3. Schrijvers EMC, Verhaaren BFJ, Koudstaal
PJ, Hofman A, Ikram MA, Breteler MMB. Is
dementia incidence declining? Trends in dementia incidence since 1990 in the Rotterdam
Study. Neurology 2012;78:1456-63.
4. Qiu C, von Strauss E, Bäckman L, Winblad
B, Fratiglioni L. Twenty-year changes in dementia occurrence suggest decreasing incidence in central Stockholm, Sweden. Neurol
ogy 2013;80:1888-94.
5. Matthews FE, Arthur A, Barnes LE, et al.
A two-decade comparison of prevalence of
dementia in individuals aged 65 years and
older from three geographical areas of En
gland: results of the Cognitive Function and
Ageing Study I and II. Lancet 2013;382:1405-12.
DOI: 10.1056/NEJMp1311405

Copyright © 2013 Massachusetts Medical Society.

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