Omega‐3 fatty acids for depression in adults

Background Major depressive disorder (MDD) is highly debilitating, difficult to treat, has a high rate of recurrence, and negatively impacts the individual and society as a whole. One potential treatment for MDD is n‐3 polyunsaturated fatty acids (n‐3PUFAs), also known as omega‐3 oils, naturally found in fatty fish, some other seafood, and some nuts and seeds. Various lines of evidence suggest a role for n‐3PUFAs in MDD, but the evidence is far from conclusive. Reviews and meta‐analyses clearly demonstrate heterogeneity between studies. Investigations of heterogeneity suggest different effects of n‐3PUFAs, depending on the severity of depressive symptoms, where no effects of n‐3PUFAs are found in studies of individuals with mild depressive symptomology, but possible benefit may be suggested in studies of individuals with more severe depressive symptomology. Hence it is important to establish their effectiveness in treating MDD. This review updates and incorporates an earlier review with the same research objective (Appleton 2015). Objectives 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. Search methods We 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). We checked reference lists and contacted authors of included studies for additional information when necessary. Selection criteria We included studies in the review if they: 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. Secondary outcomes were depressive symptomology (dichotomous data on remission and response), quality of life, and non‐completion of studies. Data collection and analysis We used standard methodological procedures as expected by Cochrane. We assessed the certainty of the evidence using GRADE criteria. Main results 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 4