Studies on the effect of fish oil on depression has previously been mixed. For this reason English scientist Julian Martins decided to update our knowledge on this subject. His research shows that the omega-3 fatty acid EPA is more effective against depression than DHA.
Martins only used high quality research in his updated meta-analysis, ie. double-blind randomized studies. His goal was to shed some light on those omega-3 studies that had shown an effect on depression, if the effect can be attributed to both EPA and DHA, or if it is only one of these two omega-3 fatty acids that works.
Martins found 28 studies that had the necessary data and the desired quality. He concludes that EPA may be more effective than DHA in treating depression, but further studies are needed to confirm this result.
Martins JG. EPA but not DHA appears to be responsible for the efficacy of omega-3 long chain polyunsaturated fatty acid supplementation in depression: evidence from a meta-analysis of randomized controlled trials. J Am Coll Nutr. 2009 Oct;28(5):525-42.
In other areas than against depression EPA and DHA work equally effectively. They are, for example both equally effective in lowering the content of fat in the blood (triglycerides). They are also both equally effective in lowering levels of inflammation in the body, and finally neither of the two fatty acids affects the body's cholesterol levels.