Mental Health Expert Dr. Charles Raison Psychiatrist,
Emory University Medical School

Expert answer

As is so often the case in this blog, the answer to your question is a resounding "maybe." Lots of studies have been done looking at omega-3 fatty acids for the treatment of both unipolar (what I sometimes call "regular old") depression and for depression in bipolar disorder. The findings are mixed.

As unclear as the data are for using omega-3 fatty acids to treat depression, we know even less about whether omega-3s might actually prevent depression.

Most of the work that has been done in this area has focused on preventing post-partum depression. Taken as a whole the results are not very promising.

I've been doing psychiatric research for a long while, and the situation with omega-3 fatty acids is far from atypical. For many reasons, a potential treatment is expected to be very promising.

Studies are done in animals that look very good. In the case of omega-3 fatty acids, numerous studies show they have just the kind of effects on brain and body functioning that should make them good antidepressants. Moreover, in the case of omega-3 fatty acids, there is evidence that people who eat food with a higher ratio of omega-3 to omega-6 fatty acids are less likely to get depressed over time.

A similar effect has been observed at the level of whole societies. Some studies show that countries that consume more fish high in omega-3s have lower rates of depression.

So people get excited about the potential new treatment and find a way to take it ahead of formal studies and swear by it. Again this is the case with omega-3 fatty acids. Then our best version of an ironclad test is applied: the placebo controlled trial. When put to this test for depression, most interventions fail. This doesn't mean they don't work.

It just means they don't work any better than a salt or sugar pill. Another way of saying the same thing is that the intervention in question doesn't have any specific antidepressant properties over and above the powerful antidepressant effects of placebo.

Placebo-controlled trials are the gold standard. But when enough of them have been done they can be lumped together into what is called a meta-analysis. In situations such as with omega-3s, where some studies are positive and some are negative, a meta-analysis sometimes allows a more accurate picture to arise.

There are two recent meta-analyses done of studies comparing omega-3 fatty acids with placebo, and even they don't agree with each other. The first, and smaller, meta-analysis found that overall omega-3 fatty acids were no more effective than placebo.

Moreover, the better quality each included study was, the less likely it was to be positive. This suggests the positive studies were mistakes.

A more recent, and larger, meta-analysis is a bit more optimistic. To make sense of its results you need to know that there are two types of omega-3 fatty acids that are most commonly used to treat depression: eicosapentaenoic acid, or EPA, and docosahexaenoic acid, or DHA. This meta-analysis found that only omega-3 preparations that were made of more than 60% EPA were effective for depression.

So a clear take-home message here is that if you do use an omega-3 fatty acid, make sure you get one that is mostly EPA.

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