The amount of high-quality evidence is insufficient for using omega-3 fatty acids to treat major depressive disorder in adults, researchers said in a Cochrane Review.
“We found a small to modest positive effect of omega-3 fatty acids, compared with placebo, but the size of this effect is unlikely to be meaningful to people with depression, and we considered the evidence to be of low or very low quality. All studies contributing to our analyses were of direct relevance to our research question, but most of these studies are small and of low quality,” Katherine M. Appleton, Ph.D., associate professor of psychology at Bournemouth University in Poole, England, and her colleagues noted in a press release accompanying the paper.
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Major depressive disorder (MDD) affects about 7% of people in Western societies and accounts for 3% of global ill health, Dr. Appleton and her colleagues reported.
Several epidemiologic and clinical studies, and randomized controlled trials (RTCs) have suggested that n-3 polyunsaturated fatty acids or omega-3 fatty acids might be a useful treatment for MDD through their effects on cell communication, neurotransmitters, and inflammation. Omega-3 fatty acids also are known to be important in brain development and function, and have been linked to depression. However, other studies have found no association between the intake of omega-3 fatty acids and depressive illness.
Dr. Appleton and her colleagues sought to understand the role omega-3 fatty acids have in the treatment of MDD by conducting a Cochrane Review of available RCTs. Their paper was published online Nov. 4 in Cochrane Database of Systematic Reviews (doi: 10.1002/14651858.CD004692.pub4).
The investigators found 26 trials with a total of 1,458 participants. In each RCT examined, the participants were randomized to receive omega-3 fatty acids or a comparator, such as a different dose of omega-3 fatty acid, placebo, or antidepressant. All included studies used a placebo except one trial, which compared omega-3 fatty acids to antidepressants. Some participants in the studies also were receiving adjunctive treatment for MDD, including antidepressants, psychotherapy, and benzodiazepines.
For the primary outcome of depressive symptoms, the effect of omega-3 fatty acids was small to modest, compared with placebo, and with only a small clinically significant effect, Dr. Appleton and her colleagues found. Meanwhile, the single study that compared antidepressants with omega-3 fatty acids found no differences between the groups for depressive symptoms.
Finally, the authors rated the quality of evidence for the outcomes to be low to very low and found that most of the studies were small and at high risk for bias.
In summary, Dr. Appleton and her colleagues found an absence of high-quality evidence to understand the impact of treatment with omega-3 fatty acids for MDD and said more complete evidence is needed. “It’s important that people who suffer from depression are aware of this, so that they can make more informed choices about treatment,” Dr. Appleton said in the press release.
“Future studies should compare [omega 3s] with usual antidepressant treatment and investigate the way these treatments may work,” they wrote in the study.
The authors report no conflicts of interest. The study was supported by Bournemouth University; the National Institute for Health Research Biomedical Research Unit in Nutrition, Diet and Lifestyle at University Hospitals; University Hospitals NHS Foundation Trust; and the University of Bristol, all in the United Kingdom.