Th e oldest old, persons living into the 10th and 11th
decades of life, are the fastest growing segment of the
population, with numbers expected to quadruple to over
8 million by 2050 . Because advancing age is a major
risk factor for dementia, this demographic shift may
signifi cantly increase the burden of dementia borne by
our society. Indeed, the dementia incidence in persons
aged 65 to 90 has been reported to double every 5 years
. However, few studies have had suffi cient numbers of
partici pants older than 90 years of age to provide accurate
estimates in the oldest old and some studies have
suggested a slowing of the incidence in the oldest old
[3,4]. Further work is thus needed to determine the
incidence of dementia in the oldest old. Th e present work
not only has important implications for public health
planning, but is also relevant for studies of etiopatho-
genesis and strate gies for prevention and treatment.
In a pivotal study addressing this question, Corrada
and colleagues present data showing that the incidence of
dementia continues to exponentially rise in the oldest old
. Th e authors studied 330 persons from Th e 90+ Study,
a longitudinal cohort study of dementia in the oldest old.
Participants were originally members of an epidemio-
logical study of a retirement community in the 1980s ;
950 of the 1,150 persons at least 90 years old in 2003 were
enrolled. Analyses for this study included only non-
demented persons at baseline, as ascertained by in-
person evaluation, who had at least one follow-up over
4 years. Th e authors found that the incident rate of dementia
increased exponentially, from 12.7% per year for 90 to
94 year olds, to 21.2% per year for 95 to 99 year olds, to
40.7% per year for persons aged 100 years and older. Th e
estimated doubling time for incidence rates was 5.5 years
and is comparable with that observed for persons aged 65
Th e results of this study contrast with other studies that
showed a slowing of dementia incidence after age 90
[7-13]. Importantly, the study has a number of strengths
that strongly support the validity of the estimate. Having
a much larger sample size, particularly for the 95 to
100 year olds and centenarians, allows for more stable
estimates of incidence rates. Additionally, 6-month inter-
vals between assessments and high follow-up rates (96%)
make it unlikely that loss to follow-up could erro neously
result in an underestimate of incidence. Th ere were some
limitations, including the selective nature of the cohort,
raising questions about selection bias and generalizability.
Th e authors note that their study population –
predominantly female, white, with high education and
socioeconomic status – is representative of individuals
aged 90+ in the US. Nonetheless, participants were
originally recruited from one retirement community and
agreed to participate in not one but two cohort studies,
making selection bias still a potential issue. Epidemiologic
studies with more racially and ethnically diverse cohorts
will be important to confi rm and extend these fi ndings.
If confi rmed, these data suggest a looming public
health crisis. How can we prevent, delay, or treat dementia
The oldest old are the fastest growing segment of the
US population but accurate estimates of the incidence
of dementia in this age group have been elusive.
Corrada and colleagues present data on the 5-year
age-specifi c rates of dementia incidence in persons
90 years and older from The 90+ Study. Their fi ndings
show a continued exponential increase in dementia
incidence after age 90 that mirrors the increase
observed in persons aged 65 to 90, with a doubling
every 5.5 years. This contrasts with previous smaller
studies reporting a slowing of the increase in incidence
after age 90. If confi rmed, the continued increase,
rather than a plateau, in the incidence of dementia in
the oldest old has implications for proper healthcare
planning. Strategies for prevention and treatment will
require more information regarding risk factors and the
etiopathogenesis of dementia in the oldest old.
© 2010 BioMed Central Ltd
Increasing incidence of dementia in the oldest old:
evidence and implications
Bryan D James1* and Julie A Schneider2
1Rush Alzheimer’s Disease Center, Room 1038, 600 South Paulina Street, Chicago,
IL 60612, USA
Full list of author information is available at the end of the article
James and Schneider Alzheimer’s Research & Therapy 2010, 2:9
© 2010 BioMed Central Ltd
in the oldest old? To better address these questions, it Download full-text
will be important to determine the pathogenesis of
dementia in the oldest old. Longitudinal clinicopathologic
epidemiologic studies suggest that dementia in older
persons is most commonly the result of mixed patholo-
gies; most commonly Alzheimer’s disease and vascular
pathology [14-16]. While there are few patho logic data
on the oldest old, a recent autopsy study in this group
showed that mixed Alzheimer’s disease and vascular
pathology continues to increase with age . Mean-
while, it has been suggested that the relationship between
Alzheimer’s disease pathology and dementia is attenuated
in the oldest old . Th is hypothesis may suggest a
greater role for vascular factors or even suggest additional
unrecognized pathologies. Further study of aging, dementia,
and pathology in longi tudinal community-based cohorts
will be needed to address these important questions.
As the fi rst major study to report that dementia
incidence continues to rise exponentially in the oldest
old, the present study has implications for how we
conceive of the relationship between aging and dementia.
It has been argued that a plateau in incidence in the
oldest old indicates that dementia is not an ‘aging-related’
process – that is, an inevitable part of aging  – but
rather an ‘age-related’ process, due to potentially
preventable age-related risk factors [4,12,13]. Yet the
distinction between these two concepts may be artifi cial.
Indeed, the continued rise in incidence could result from
the continued accumulation of age-related risk factors
eventually surpassing the brain’s compensatory facilities
(that is, reserve capacity). In addition, even if some
components of the pathologic process are inevitable,
given the possible continued accumulation of Alzheimer’s
disease and mixed pathologies, it remains quite feasible
that targeted strategies could prevent, delay, or treat at
least part of the dementing process in the oldest old.
After all, public health initiatives have dramatically
pushed back the average age of death, the most inevitable
conse quence of aging.
JAS is a neuropathology consultant for AVID Radiopharmaceuticals, Inc. and
is on the Alzheimer’s Medical Advisory Board for GE Healthcare. The authors
declare no other competing interests.
1Rush Alzheimer’s Disease Center, 600 South Paulina Street, Room 1038,
Chicago, IL 60612, USA. Department of Medicine, Rush University Medical
Center, Chicago, IL, USA. 2Rush Alzheimer’s Disease Center, 600 South Paulina
Street, Suite 1022F, Chicago IL 60612, USA. Departments of Pathology
(Neuropathology) and Neurological Sciences, Rush University Medical Center,
Chicago, IL, USA.
Published: 13 May 2010
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Cite this article as: James BD, Schneider JA: Increasing incidence of
dementia in the oldest old: evidence and implications. Alzheimer’s Research
& Therapy 2010, 2:9.
James and Schneider Alzheimer’s Research & Therapy 2010, 2:9
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