Fish is a vital source of the long-chain omega-3 fatty acid EPA, which is crucial for balancing the mood-enhancing neurotransmitter serotonin (it has a similar action to SSRIs – selective serotonin re-uptake inhibitors). One of the purposes of omega-3 fats is to ensure that cell membranes in the brain and body are functioning fluidly and allowing electrical messaging to function properly.
Depressive symptoms can occur when low levels of EPA create a chemical imbalance in the brain, which affects the production of mood-stabilising neurotransmitters. In addition, people with depression often have increased levels of inflammation, which is associated with symptoms such as fatigue, fever, lack of sleep, pain, and aching. EPA in fish oil is especially helpful in this respect, since it is converted within the body to anti-inflammatory eicosanoids and helps to tackle these specific symptoms. Taking a purified high-EPA fish oil may bring about improvements in the following:
- Low mood
- Sleep problems
- Poor libido
- Immune function
What evidence is there?
Experts believe that the average Western diet is a major factor in the development of certain mental health problems, which affect one in four of us in the UK each year.  When comparing the average Western diet to that which is typical in the Far East, it appears that our diets fall somewhat short. Scientists suggest that one of the reasons for the low rate of depression in the Far East is their high intake of omega-rich oily fish. With an incidence of 6%, depression is 60 times more common in New Zealand where fish consumption is very low, when compared with Japan, where it affects just 0.12% of the population. Not surprisingly, it is well established that there is a direct correlation between omega-3 deficiency and depressive symptoms. 
Such evidence has led to a plethora of clinical trials using omega-3 supplements to alleviate symptoms in sufferers. The results from trial to trial have often given conflicting and sometimes confusing results, however. Several factors appear to account for the discrepancies between studies: the length of the treatment, the amount of omega-3 used but most importantly the type of omega-3 within the supplement. Two major review papers have investigated these discrepancies [4,5] and have found that the ratio of EPA:DHA is of significance when establishing the efficacy of a supplement in the treatment of depression; the higher the EPA to DHA content, the better the efficacy. EPA has to be in excess of DHA to show benefit.
Several studies have demonstrated how effective pure EPA supplementation is for people with depression, ranging from those with mild or moderate depression, to those with severe depression and bipolar disorder. A minimum dose of 1g pure ethyl-EPA daily is required over a period of three months to produce significant benefits and The American Psychiatric Association has since recommended treatment with at least 1g/day of omega-3 for these conditions as an addition to standard treatment.
A double blind, randomised trial has shown that the omega-3 EPA is as effective as Prozac in the treatment of depression and, when used in combination, is even more effective. The same group duplicated these findings two year later showing ethyl-EPA’s ability to improve symptoms and reduce levels of both cortisol and inflammatory markers.  The use of pure ethyl-EPA has also been shown to be particularly effective in individuals who do not respond to conventional pharmaceutical medication. [8,9]
What we recommend
E-EPA 90 is the purest ethyl-EPA concentrate available without prescription, suitable for counteracting omega-3 deficiencies offering a safe and effective treatment for depression. An initial 3-month loading dose of pure EPA is recommended before switching to Vegepa E-EPA 70 for long-term maintenance and to ensure EPA levels and mood remain stable.
 The Office for National Statistics Psychiatric Morbidity report (2001).
 Hibbeln JR. (1998) Fish consumption and major depression. Lancet. 18:1213.
 McNamara RK. (2011) Long-Chain Omega-3 Fatty Acid Deficiency in Mood Disorders: Rationale for Treatment and Prevention. Current Drug Discovery Technologies [Epub ahead of print]
 Martins JG. (2009) 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 randomised controlled trials. Journal of the American College of Nutrition. 28:525-42. Review.
 Sublette ME, Ellis SP, Geant AL &Mann JJ. (2011) Meta-analysis of the effects of eicosapentaenoic acid (EPA) in clinical trials in depression. Journal of Clinical Psychiatry.72:1577-84.
 Jazayeri S, Tehrani-Doost M, Keshavarz SA, Hosseini M, Djazayery A, Amini H, Jalali M & Peet M. (2008) Comparison of therapeutic effects of omega-3 fatty acid eicosapentaenoic acid and fluoxetine, separately and in combination, in major depressive disorder. Australian and New Zealand Journal of Psychiatry. 42:192-8.
 Jazayeri S, Keshavarz SA, Tehrani-Doost M, Djalali M, Hosseini M, Amini H, Chamari M & Djazayery A. (2010) Effects of eicosapentaenoic acid and fluoxetine on plasma cortisol, serum interleukin-1beta and interleukin-6 concentrations in patients with major depressive disorder. Psychiatry Research. 178:112-5.
 Puri BK, Counsell SJ, Hamilton G, Richardson AJ & Horrobin DF. (2001) Eicosapentaenoic acid in treatment-resistant depression associated with symptom remission, structural brain changes and reduced neuronal phospholipid turnover. International Journal of Clinical Practice. 55:560-3.
 Puri BK, Counsell SJ, Richardson AJ & Horrobin DF. (2002) Eicosapentaenoic acid in treatment-resistant depression. Archives of General Psychiatry. 59:91-2.