From the abstract of a 2003 article titled “A Double-Blind, Placebo-Controlled Study of the Omega-3 Fatty Acid Docosahexaenoic Acid in the Treatment of Major Depression”:
Thirty-six depressed patients were randomly assigned to receive DHA, 2 g/day, or placebo for 6 weeks. Response was defined a priori as a >=50% reduction in the score on the Montgomery-Åsberg Depression Rating Scale. Thirty-five participants were evaluable; 18 received DHA, and 17 received placebo. RESULTS: Response rates were 27.8% in the DHA group and 23.5% in the placebo group. The difference in response rates between groups did not reach statistical significance. CONCLUSIONS: This trial failed to show a significant effect of DHA monotherapy in subjects with major depression.
This study is unusual in that it used DHA rather than EPA. EPA studies have been more successful. Excerpt from an overview:
One meta-analysis combined all the studies involving adults with unipolar or bipolar depression reported above, in which omega-3 fatty acids were used to augment existing treatments or as monotherapy. Best-case and worst-case analyses were carried out, and omega-3 fatty acids were found to produce a statistical improvement compared to placebo under both scenarios (best-case p = 0.02, worst-case p = 0.03). A second review including the same data has also suggested a benefit of omega-3 fatty acids in major depression. However, as the authors of both reviews point out, there is significant heterogeneity among the included trials, and this undermines the reliability of the combined results.
Here is the conclusion from another review article:
Trial evidence that examines the effects of n–3 PUFAs on depressed mood is limited and is difficult to summarize and evaluate because of considerable heterogeneity. The evidence available provides little support for the use of n–3 PUFAs to improve depressed mood.
A weak effect, in other words. I would be surprised if omega-3s helped a lot with depression. My self-experimentation pointed to a different cause of depression — seeing faces too little in the morning and/or too much at night.
You point out that the Pennsylvania Amish have a one-year rate of unipolar depression of about 0.1 percent (page 238 of your paper).
I guess it’s a pretty safe bet the Amish don’t consume large amounts of either fish or flaxseed oil.
Or eat a lot of fish. Yeah, good point. Someone should measure their omega-3 levels. The Amish don’t have unusually low rates of bipolar disorder. Bipolar disorder might be more sensitive to omega-3 than unipolar depression. There is a large cross-national negative correlation between rate of bipolar disorder and fish consumption, if I remember correctly.