The use of omega-3 fatty acids for the treatment of depression is not a recommendation in depression treatment guidelines. A very thorough meta-analyses published last year, which excluded confounding factors that were problematic in many previous studies, found no beneficial effect of omega-3 fatty acids in the treatment of depression.1 Most positive results came from lower quality studies and were the result of publication bias or statistical adjustment. The authors don’t exclude the possibility that there’s a genetic component to the effect of omega-3 and that therefore certain populations might benefit more than others. Epidemiological studies do show lower rates of depression in countries where polyunsaturated fatty acids (omega-3 or omega-6) are common in the local diet.
There are two forms of omega-3 on the market, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). A very recent meta-analysis, published in December,2 categorized omega-3 supplements according to their composition, and found a significant benefit in depression from those supplements that were more than 60% EPA, with no benefit in those under 60% EPA. Other studies have shown similar results,3 but there’s still a tendency for the strongest effects to appear in the lowest quality studies. In the latest study, improvement was determined by the dose of EPA in excess of DHA, and supplements were effective in which EPA exceeded DHA by 200 to 2,200 mg/d.