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 “A number of other reviews investigating the impact of omega-3 fatty
acids on depression and depressive disorders have also been
conducted, and all of these also find discrepancies between studies,
and inconsistencies in findings, and essentially find it difficult
to draw convincing conclusions,” said lead author Katherine Appleton
of the University of Bournemouth in the U.K.
“All reviews also conclude with the need for further evidence,” she
said.
The new review included 26 randomized controlled trials involving
almost 1,500 adults with major depressive disorder in total. The
trials compared people who were given omega-3 fatty acid capsules
and people given placebo pills.
Only one study compared omega-3 capsules to an antidepressant
medication.
While people who took the omega-3 capsules did report lower levels
of depression symptoms compared to the placebo group, there was only
a small difference that would likely not be meaningful for most
people, the authors write in the Cochrane Library.
Side effects and adverse events may have increased for some people
taking omega-3 capsules, but the results varied widely from study to
study. The quality of evidence from each study was low to very low,
in the authors’ rating.
In the one study including antidepressants, there was no difference
between omega-3 fatty acid supplements and antidepressants for
depressive symptoms.
The results are “promising, but not conclusive,” said Giuseppe
Grosso, a nutritional epidemiologist at the University of Catania in
Italy, who was not part of the review.
It’s not clear why, or how, the omega-3 fatty acids naturally found
in fish oils would improve depressive symptoms, although
inflammation and cell communication changes, among other pathways,
have been suggested, Appleton told Reuters Health by email.
“One of the problems with understanding results from clinical trials
in general is that they are looking for an average effect, while
many experts agree that the ideal approach would be to figure out
which subsets of depressed patients could benefit from particular
treatments, an approach the (National Institutes of Health) has
called 'personalized medicine',” said Dr. Elizabeth Sublette of
Columbia University in New York, who was not part of the new review.
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“At this stage we don't yet know how to predict which depressed
patients will respond to omega-3 supplements,” Sublette told Reuters
Health by email. “They remain one potential treatment that may be
worth trying, and I would encourage both doctors and patients to
keep an open mind about this topic until more evidence of higher
quality can be obtained.”
Most omega-3 supplements are composed of natural oils, so there is
no evidence to suggest the results of the trials would have been
different if the omega-3 acids came from eating fish rather than
taking capsules, she said.
A bottle of 50 to 100 capsules of omega-3 fish oil supplement costs
between $10 and $20 at most drugstores.
More research is needed to assess the potential positive and
negative effects of using these supplements to treat major
depressive disorder, Appleton and her colleagues write.
“Many possible treatments for depression are currently being
investigated, but the evidence for many of these treatments is still
incomplete,” she said.
SOURCE: http://bit.ly/1HFLp0f The Cochrane Library, online November
5, 2015.
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