Are fish oil supplements containing lots of omega-3 fatty acid a viable way to help prevent depression? According to new research, the answer is no. The largest ever clinical trial of its kind reports there is no validity to the claim that omega-3 supplements help prevent depression.

Doctors sometimes recommend omega-3 supplements for patients at “high-risk” for developing depression. However, there is no set guideline for their use as a depression treatment. This is mainly due to most relevant studies producing mixed findings at best.

So, in an effort to form a clearer idea of the relationship between depression and omega-3 supplements, scientists from both Massachusetts General Hospital and Brigham and Women’s Hospital put together the Vitamin D and Omega-3 Trial-Depression Endpoint Prevention (VITAL-DEP). The project aimed to determine if a daily omega-3 supplement or a vitamin D supplement would help impede depression.

In all, 18,353 adults over 50 years-old participated in this work. Each adult was not dealing with depression at the start of the study. From there, researchers randomly assigned the volunteers to groups receiving either a daily vitamin D or omega-3 supplement or a placebo for about 5.3 years.

“This study is a significant step. It requires many thousands of people to conduct this type of study of preventing depression in adults—something we call universal prevention—and the participants were taking randomized study pills for between 5 to 7 years on average,” says VITAL-DEP lead investigator and lead study author Dr. Olivia Okereke, the director of geriatric psychiatry at MGH, in a media release. “So, it is rare to see a long-term randomized trial of this kind.”

Omega-3 can be useful, but not for mental health

Ultimately, all that research showed no benefit at all linked to the omega-3 supplements in terms of either preventing depression or provoking any type of tangible mood boost.

“There was no harmful or beneficial effect of omega-3 on overall course of mood during the roughly 5 to 7 years of follow-up,” Dr. Okereke notes.

Still, study authors make a point to note that this work doesn’t mean omega-3 supplements don’t provide other health benefits.

“There are still health reasons for some people, under the guidance of their health care providers, to take omega-3 fish oil supplements. For example, these supplements increasingly have been found to have benefits for cardiac disease prevention and treatment of inflammatory conditions, in addition to being used for management of existing depressive disorders in some high-risk patients,” concludes senior author JoAnn Manson, MD, DrPH, chief of the Division of Preventive Medicine at BWH, a professor of medicine at Harvard Medical School, and director of the parent VITAL trial.

“However, our findings indicate there is no reason for adults without depression in the general population to take fish oil supplements solely for the purpose of preventing depression or for maintaining a positive mood.”