Docosahexanoic Acid is DHA, an omega-3 essential fatty acid that is found in fish oil. A number of studies have linked it to improved mood and cognition. A number of earlier studies have associated low omega-3 levels. Research appearing in Biological Psychiatry (1 July 2007; Volume 62, Issue 1, Pages 17-24) actually looked at the DHA content in the frontal lobes of deceased patients with major depressive disorder (on autopsy) and compared the fatty acid content in deceased patients without depression. The only fatty acid that was significantly different between the two groups was DHA, which was 22% lower in the depressed patients.