Vitamin d and fish oil fail to prevent depression in massive trial

NCT ID NCT01696435

Completed Prevention Sponsor: Brigham and Women's Hospital Source: ClinicalTrials.gov ↗

First seen Jun 27, 2026 · Last updated Jun 27, 2026

Summary

This study tested whether taking daily vitamin D or fish oil supplements could prevent depression in over 18,000 adults without significant mood issues at the start. Participants were followed for about 5 years. The results showed that neither supplement reduced the risk of developing depression or improved mood scores compared to a placebo.

What this could mean

Our plain-language read of the trial. This is informational only — not medical advice or a prediction.

Active substance: vitamin D3 (2000 IU daily) and omega-3 fatty acids (fish oil, 1 gram daily)
What this could lead to: If effective, these common supplements could offer a simple, low-cost way to help prevent depression in the general population.
What could go wrong: This large, completed trial found no significant reduction in depression risk or improvement in mood scores with either supplement compared to placebo.

This is an AI summary of the original study and may miss details. Read our disclaimer.

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Conditions

The condition(s) this trial relates to.

Depression mood disorder depressive disorder prevention target

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

DEPRESSION DEPRESSIVE SYMPTOMS MOOD

Contacts and locations

Locations

Brigham and Women's Hospital

Boston, Massachusetts, 02215, United States

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