Can Omega-3 fatty acids help elevate depression?

UK: Results from a Cochrane review suggest that there is an absence of sufficient high-quality evidence to determine the effects of n-3 polyunsaturated fatty acids (n-3PUFAs; also known as omega-3 fatty acids) as a treatment for major depressive disorder (MDD). The researchers found a small-to-modest positive effect of n-3PUFAs compared to placebo, but the effect is unlikely to be meaningful for MDD patients. 

According to the authors, the evidence was very low or very low certainty, with many differences between studies. Also, there was insufficient high-quality evidence to determine the effects of n-3PUFAs on negative side effects or numbers not completing studies.

Major depressive disorder is a mental health disorder characterized by a markedly decreased pleasure or interest in all activities or depressed mood, or both. It has negative impacts on the individual and on society, often over the long term. Some studies have suggested n-3PUFAs (also known as omega-3 oils), naturally found in fatty fish, seafood, and in some nuts and seeds, to be a possible treatment. Various lines of evidence suggest that n-3PUFAs may impact depressive symptoms, but a lot of studies have different findings, making it difficult to draw conclusions.

Against the above background, Appleton KM and colleagues aimed to assess the effects of n-3 polyunsaturated fatty acids (also known as omega-3 fatty acids) versus a comparator (e.g. placebo, antidepressant treatment, standard care, no treatment, wait-list control) for major depressive disorder (MDD) in adults. The review updates and incorporates an earlier review with the same research objective (Appleton 2015). 

The researchers searched the Cochrane Central Register of Controlled trials (CENTRAL), Ovid MEDLINE, Embase and PsycINFO together with trial registries and grey literature sources (to 9 January 2021). 

The studies were included in the review if they met the following inclusion criteria -- if used a randomised controlled trial design; provided n-3PUFAs as an intervention; used a comparator; measured depressive symptomology as an outcome; and were conducted in adults with MDD.

Primary outcomes were depressive symptomology (continuous data collected using a validated rating scale) and adverse events. 

The review includes 35 relevant studies: 34 studies involving a total of 1924 participants investigated the impact of n-3PUFA supplementation compared to placebo, and one study involving 40 participants investigated the impact of n-3PUFA supplementation compared to antidepressant treatment. 

"We need more evidence, particularly to explain the differences between study findings, e.g. by looking at individuals who may or may not benefit from n-3PUFAs," the authors concluded. "Future studies should also compare n-3PUFAs with usual antidepressant treatment, and investigate the way these treatments may work."