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DHA
'fish oil' supplements do not seem to slow
cognitive, functional decline in Alzheimer's
disease
November 2010--Patients with mild to moderate Alzheimer's
disease (AD) who received supplementation
with the omega-3 fatty acid docosahexaenoic
acid (DHA), believed to possibly reduce the
risk of AD, did not experience a reduction
in the rate of cognitive and functional
decline, compared to patients who received
placebo, according to a study in the
November 3 issue of JAMA,
a theme issue on aging.
Joseph F. Quinn, M.D., of Oregon Health and Science
University and the Portland VA Medical
Center, Portland, Ore., presented the
findings of the study at a JAMA media
briefing at the National Press Club.
"Several studies have found that consumption of fish, the
primary dietary source of omega-3 fatty
acids, is associated with a reduced risk of
cognitive decline or dementia.
Some studies have found that consumption of DHA, but not
other omega-3 fatty acids, is associated
with a reduced risk of Alzheimer disease,"
the authors write.
However, those studies were observational and did not
control who received DHA. Animal studies
that used DHA showed reductions in
Alzheimer-like brain pathology.
Dr. Quinn and colleagues conducted a randomized, controlled
trial to examine whether DHA supplementation
would slow the rate of cognitive and
functional decline in individuals with
Alzheimer's disease.
The study, which was conducted between November 2007 and
May 2009 at 51 U.S. clinical research sites,
included 402 individuals with mild to
moderate Alzheimer's disease.
Participants were randomly assigned to DHA at a dose of 2
grams/day or to identical placebo (60
percent were assigned to DHA and 40 percent
were assigned to placebo).
Duration of treatment was 18 months. Changes in cognitive
and functional abilities were assessed with
the Alzheimer's Disease Assessment Scale
(ADAS-cog) and the Clinical Dementia Rating (CDR) sum of
boxes. Rate of brain atrophy was also
determined by volumetric magnetic resonance
imaging (MRI) in a subsample of
participants.
A total of 295 participants completed the trial while
taking study medication (DHA: 171; placebo:
124).
The researchers found that supplementation with DHA had no
beneficial effect on rate of change on ADAS-cog
score, with the rate of average change in
the score over 18 months being 8.27 points
for the placebo group and 7.98 points for
the DHA group. The rate of points change on
CDR sum of boxes over 18 months was 2.93 for
the placebo group compared with 2.87 for the
DHA group.
Among the individuals participating in the MRI substudy
(102 had MRIs at the beginning of the study
and at 18 months [DHA group: 53; placebo
group: 49]), an analysis showed no effect of
DHA treatment on total brain volume change
during 18 months.
"In summary, these results indicate that DHA
supplementation is not useful for the
population of individuals with mild to
moderate Alzheimer disease," the authors
write.
The researchers add that "because part of the rationale for
the trial was epidemiological evidence that
DHA use before disease onset modifies the
risk of Alzheimer disease, it remains
possible that an intervention with DHA might
be more effective if initiated earlier in
the course of the disease in patients who do
not have overt dementia."
Editor's Note: Please see the article for additional
information, including other authors, author
contributions and affiliations, financial
disclosures, funding and support, etc.
Editorial: Treatment of Alzheimer Disease
and Prognosis of Dementia
In an accompanying editorial, Kristine Yaffe, M.D., of the
University of California, San Francisco and
Veterans Affairs Medical Center, San
Francisco, comments on the findings of this
study.
"This trial adds to a growing literature that treatment
with DHA does not improve symptoms of AD.
Although several observational studies
reported that diets rich in fish or
supplements with omega-3 fatty acids were
associated with reduced risk of developing
AD, most randomized clinical trials for
treatment of AD or mild cognitive impairment
or in healthy elderly individuals have not
found a beneficial effect."
