What is the effectiveness of the use of polyunsaturated fatty acid omega-3 in the treatment of depression?

This systematic review aims to identify the effect of polyunsaturated fatty acid omega-3 on depressive disorder. A bibliographical search was conducted in the databases SciELO, PubMed and ISIWEB. The keywords used were: "depression" and "omega-3 fatty acids", "depression" and "omega-3 polyunsaturated fatty acid", "depression" and "n-3 fatty acids". A total of 19 studies were identified: four double-blind randomized studies, four cohorts, two cross-sectional lines and nine case-controls. Only five studies presented dropout of less than 30% and controlled for the most important confounding variables. Of the evaluated studies, 13 showed a significant positive association between omega-3 and depression, while six studies did not show a relationship between the referred variables. Therefore, future studies with similar methodology would aid in determining the precise effect of omega-3 on depressive disorders.