WEDNESDAY, Feb. 14 (HealthDay News) -- There's no evidence that omega-3 fatty acids on their own fight depression and only limited evidence that they're effective against depression when used in combination with antidepressant drugs, according to new research.

Previous studies had suggested an association between omega-3 levels and behavior and mood disorders, including depression, according to background information in the review article, published in the journal Drug and Therapeutics Bulletin.

Omega-3 fatty acids play a role in chemical signaling in the brain, and also help regulate blood vessel activity and immune system function linked to the central nervous system. Oily fish, nuts, seeds, and leafy green vegetables are the main dietary sources of omega-3, which is also available in dietary supplements that contain fish oil.

The review authors analyzed published studies on the clinical effectiveness of omega-3 in people with depression.

Along with their conclusion that omega-3 has little or no effect on depression, the authors said there is evidence that fish oil supplements contain environmental toxins, which may be especially concentrated in supplements made from fish livers.

This means that people should not exceed the maximum recommended doses of these supplements, the authors said. They also noted that pregnant women should take only low doses of fish oil supplements, which contain vitamin A. High levels of vitamin A can harm a developing fetus.

More information

The U.S. National Library of Medicine has more about omega-3 fatty acids.