Since omega-3 fatty acids are essential fatty acids (EFA) that cannot be synthesized to a large degree in the body from other dietary substance, the limiting factor in determining tissue concentrations is the amount of omega-3 fatty acids in the diet. Omega-3 and omega-6 are both constituents of many tissues and, in some sense, compete for incorporation into tissue.

In the last 100 years or so, there has been a large increase in the dietary consumption of the omega-6 fatty acids due to alteration of farming and animal feed. The increase in the incidence of depression over these years parallels the increase of omega-6, so that much more omega-6 is consumed relative to omega-3 EFA’s. Hence, an omega-3 EFA dietary deficit may be a risk factor for depression.

We will present a meta-analysis of randomized, double-blind-placebo-controlled studies testing the administration of omega-3 EFA for the treatment of depression. We performed a systematic literature search, subdividing studies as those which used an EPA predominant or a DHA formulation.

Omega 3 is more effective than placebo in treating depressive illness, although there is some variability in results. We explored whether the composition of the omega-3 administered is important, finding that EPA predominant formulation is necessary for the full therapeutic antidepressant action with a large effect size, with little variability. The DHA predominant formulation has little antidepressant efficacy.

We conclude that omega-3 does have antidepressant properties. We will also discuss the role of omega-3 in depression or other disorders, in the broader range of ecological, epidemiological and experimental context, focusing on findings that have implication on cellular mechanism of antidepressant action or in disease.