If you’re feeling depressed, you might feel better if you take fish oil supplements, a new study shows.

Some patients in the study, but not all, got relief from the omega 3 fatty acids in the fish oil. The ones who did improve - about half the group - were those who didn’t also have a diagnosis of an anxiety disorder.

The other half - depressed people who had anxiety disorders, too - didn’t get any clear benefit from taking the supplements compared to placebo.

These findings, published in the Journal of Clinical Psychiatry, add to the confusion about whether omega-3 fatty acids really help depression. Different studies have reported conflicting results. At least some of the confusion is due to the fact that researchers rarely test these substances in any standard way. Some studies have looked at omega-3 as a stand-alone therapy; others have tested it in combination with antidepressants. The formulations often vary, too.

According to the researchers involved in the current study, some of the strongest evidence of benefit has come from supplements rich in EPA - which, along with DHA, is one of the two main forms of omega-3 fat. (EPA stands for eicosapentaenoic acid, and DHA stands for docosahexaenoic acid.)

So they tested a fish-oil capsule with a high ratio of EPA to DHA, providing 1,050 milligrams per day of the former and 150 mg per day of the latter. All 432 patients in the study had been diagnosed with at least moderate depression. About 40 percent were already on antidepressants.

Dr. Francois Lesperance, of the University of Montreal in Canada, who directed the current study, and his colleagues randomly assigned patients to take either the fish-oil capsules or a placebo containing vegetable oil every day for eight weeks.

At the beginning of the study and several points throughout, patients completed a standard questionnaire gauging the severity of depression symptoms.

When the researchers looked at results from everyone in both groups, there was no clear difference between fish oil and placebo. But among anxiety-free patients, symptoms improved significantly more with fish-oil than with the placebo.

Patients with anxiety disorders - such as generalized anxiety, phobias, post-traumatic stress disorder and panic disorder - did not do better on fish oil.

Taking anti-depressants, or not taking them, did not affect the results.

The study is the largest so far to test the effects of omega-3 fatty acids on depression symptoms, Lesperance told Reuters Health by email.

Still, the ultimate role of fish oil in treating depression, if any, remains unclear. Further clinical trials - including ones that compare fish oil with antidepressant therapy - are still needed, according to Lesperance and his colleagues.

Lesperance also noted that the findings apply to the EPA-rich supplement used in the study, and not necessarily to any fish-oil pill on the market, which range in the amount and balance of EPA and DHA.

Fish oil supplements, while much less expensive than prescription antidepressants, can also have dangerous side effects - including an increased risk for bleeding - when taken in doses that are too high.

Lesperance advised that people with depression who are interested in trying fish oil first talk with their doctors. Patients on antidepressants should not stop taking them on their own, he said.

It is not entirely clear why omega-3 fatty acids, particularly EPA, might be helpful for some cases of depression.

Some research has suggested that the fatty acids are involved in the function of certain brain chemicals linked to depression. It’s also possible that the anti-inflammatory effects of fish oil are at work, according to Lesperance’s team.

The study was partially funded by Isodis Natura, maker of the fish-oil supplement tested. Several of the researchers have served as consultants to drug companies that market antidepressants.

SOURCE: Journal of Clinical Psychiatry, online June 15, 2010.