WEDNESDAY, Dec. 8 (HealthDay News) -- Omega-3 fatty acids may help alleviate depression but only when a particular type of fatty acid called DHA is used in the right ratio with another fatty acid known as EPA, a new study suggests.
The researchers analyzed the results of some 15 previous controlled clinical trials on the use of omega-3s -- commonly found in oily fish or in fish oil supplements -- to treat depressed people.
They found that when used by itself, DHA (docosahexaenoic acid) alone did not seem to offer any benefit. However, DHA combined with a rather high dose of EPA (eicosapentenoic acid) did improve depressive symptoms.
"Preparations with some EPA had some consistent antidepressant effects, while preparations of pure DHA had no antidepressant effects," said lead study author Dr. John Davis, a professor of psychiatry at the University of Illinois at Chicago. "I don't think we can prove it beyond a shadow of a doubt, but there is now evidence from a number of double-blind studies that suggest mixed DHA/EPA has antidepressant properties, whether by itself or given along with traditional antidepressants."
The study, funded by the U.S. National Institutes of Health, was designed as a meta-analysis, in which researchers combine the results of multiple prior studies. The findings were slated for presentation Thursday at the American College of Neuropsychopharmacology meeting in Miami.
Davis noted the next step should be to test the anti-depressant effect of the omega-3 fatty acid combination in a large population to establish a dose range.
Prior research on the effectiveness of omega-3 fattys acids against depression has been mixed, with one recent randomized, placebo-controlled clinical trial in the Journal of the American Medical Association, for example, concluding that taking 800 milligrams of DHA daily did not help ward off depression in pregnant women.
Epidemiological studies, in which researchers look for associations across populations, have linked DHA deficiencies to depression. However, it's unknown if the depressed people in the study were DHA-deficient and therefore the supplements were simply returning their DHA levels to normal, or if an added boost of DHA/EPA was helpful even for those with sufficient levels, Davis said.
Also unknown is whether depressed individuals could use a DHA/EPA combination instead of standard antidepressant medications or if it could or should be used to augment other medications, said Edythe London, a professor of psychiatry and pharmacology at University of California, Los Angeles.
London cautioned that depressed individuals should certainly not rely on fish oil supplements alone.
"The consistent finding is omega-3 fatty acids can improve the mood of people who have depression symptoms," London said. "But depression is a very serious disorder. If someone is depressed, they should not just buy something off the shelf and rely only on that. They should be evaluated by their mental health professional who can determine the most appropriate course of therapy."
And DHA/EPA did not improve the mood of study participants who were not depressed, Davis noted.
Cold-water oily fish such as salmon, tuna, sardines, trout and herring contain both DHA and EPA. A few other foods contain those nutrients as well, including nuts, soybeans and flaxseed.
Fish oil supplements containing DHA are also among the most popular supplements, Davis said. He recommended people look for one that has relatively equal amounts of both EPA and DHA.
Since the findings are to be presented at a medical meeting, they should be considered preliminary until published in a peer-reviewed journal.
The U.S. National Institute of Mental Health has more on depression.
SOURCES: John Davis, M.D., professor, psychiatry, University of Illinois at Chicago; Edythe London, Ph.D., professor, psychiatry and pharmacology, University of California, Los Angeles, Los Angeles, Calif.; meeting, American College of Neuropsychopharmacology meeting, Dec. 8, 2010, Miami
All rights reserved