Alzheimer's, Dementia & Mental Health
Seniors with
Less Education and Lower Levels of Biomarker Suffer Greater Cognitive
Decline
'To identify those
at risk of dementia, biomarkers like plasma beta-amyloid level that are
relatively easy to obtain and minimally invasive could be useful'
Jan. 18, 2011 -
Older adults without dementia and with lower levels in blood plasma of
the biomarkers beta-amyloid 42/40 (protein fragments) had an increased
rate of cognitive decline over a period of 9 years, according to a study
in the January 19 issue of the Journal of the American Medical
Association (JAMA). They also found this relationship stronger among
individuals with less education and lower levels of literacy.
An estimated 36
million people currently have dementia, with the prevalence expected to
double every 20 years, according to background information in the
article.
"Thus,
biomarkers to identify elderly persons at risk of developing dementia
could be useful for early prevention, if and when such interventions are
available, and treatment," the authors write.
"Lower plasma
beta-amyloid 42 and 42/40 levels have been associated with incident
dementia, but results are conflicting and few have investigated
cognitive decline among elders without dementia."
The study to
investigate the association between plasma beta-amyloid 42 and 42/40
levels and cognitive decline in a large group of community-dwelling
older adults without dementia, was conducted by Kristine Yaffe, M.D., of
the University of California, San Francisco, and San Francisco Veterans
Affairs Medical Center, and colleagues.
They also
examined whether measures of cognitive reserve, as indicated by levels
of education and literacy attained, modified the association of plasma
beta-amyloid level with cognitive decline.
The analysis
included 997 black and white community-dwelling older adults who were
enrolled in the Health ABC Study, a prospective observational study
begun in 1997-1998 with 10-year follow-up in 2006-2007.
The study
participants had the following characteristics:
● average age was 74 years;
● 55.2 percent (550) were female; and
● 54 percent (538) were black.
Measures of
beta-amyloid 42 and 42/40 and cognitive function (via Modified
Mini-Mental State Examination) were obtained.
The researchers
found that low beta-amyloid 42/40 level was associated with greater
cognitive decline over 9 years. After adjustment for several factors,
the results remained statistically significant.
There was also a
significant association between plasma beta-amyloid 42 levels and
cognitive decline. There was no association between plasma beta-amyloid
40 levels and baseline cognitive function or decline.
Also, cognitive
reserve measures modified the association between beta-amyloid 42/40
level and cognitive decline. Older adults with low reserve (as measured
by less than a high school diploma or sixth-grade or lower literacy) had
an even greater association with beta-amyloid 42/40 level, whereas those
with high reserve had less association.
"These results
are important, as the prevalence of cognitive impairment is increasing
exponentially and prevention will be crucial. To identify those at risk
of dementia, biomarkers like plasma beta-amyloid level that are
relatively easy to obtain and minimally invasive could be useful,” the
author’s write.
“In addition,
our finding of an interaction of cognitive reserve with the association
of plasma beta-amyloid level and cognitive decline could have public
health importance because it may suggest pathways for modifying
beta-amyloid effects on cognition," such as with cognitive activity or
ongoing education, according to the study.
"Future studies
should further explore the use of plasma beta-amyloid as a biomarker,
assess the mechanisms by which cognitive reserve modifies this
association, and determine whether increasing cognitive reserve through
interventions can reduce the risk of Alzheimer disease."
Editorial:
Mapping Out Biomarkers for Alzheimer Disease
"Of interest in
relation to the study by Clark et al is that the relationship of
beta-amyloid 42/40 and cognitive decline was modified by cognitive
reserve, further evidence that for Alzheimer disease, the presence of
pathology is not the whole story,” says an editorial in the same JAMA
issue.
“The most
important message from this and similar studies is that differences in
proteins and peptides can be found in peripheral fluids years before
clinical onset of dementia."
The editorial
was by Monique M. B. Breteler, M.D., Ph.D., of Erasmus MC, University
Medical Center Rotterdam, the Netherlands, and the German Center for
Neurodegenerative Diseases, Bonn, Germany.
