Several double-blind, placebo-controlled trials have studied the efficacy of omega-3
supplementation in adults with MDD. In 2006-2007, three meta-analyses reported a
significant benefit of omega-3 fatty acids for the treatment of depressed mood. These
meta-analyses suggested a modest effect size of treatment (effect size: 0.13-0.61), a large
degree of heterogeneity between studies, and evidence of publication bias in the
literature. These meta-analysis also included trials that examined depressed mood as an
outcome in patients with other primary psychiatric disorders such as bipolar disorder,
schizophrenia, obsessive-compulsive disorder, personality disorders or chronic fatigue
syndrome. Since these meta-analyses were published, there have been at least 9 additional
randomized, placebo-controlled trials examining the efficacy of omega-3 fatty acids for
MDD. The addition of these trials more than doubles the sample size of previous metaanalyses
and gives us the power to examine the efficacy of omega-3 FAs in MDD
specifically. Two recent meta-analyses reported significant treatment benefits of omega-3
fatty acids in depressed mood consistent with the earlier studies (effect size: 0.10-0.47), but
still included patients with other primary psychiatric disorders and failed to adjust for
publication bias.Trials that report on depressive symptoms as a secondary outcome in
other psychiatric illnesses may be particularly prone to publication bias as authors are less
likely to analyze and report secondary measures that are non-significant and therefore noninformative.
Furthermore, adding trials in which exclusively included individuals with other
primary psychiatric disorders will likely increase heterogeneity between trials.