Baseline blood levels of omega-3 and depression remission: A secondary analysis of data from a placebo-controlled trial of omega-3 supplements

Objective: Depression is associated with low red blood cell (RBC) levels of 2 omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), suggesting that omega-3 supplements might improve depression. However, clinical trials have produced mixed results. The purpose of this secondary analysis of data from a randomized controlled trial was to determine whether baseline blood levels of omega-3, which are known to vary widely among individuals, predict depression outcomes. Method: The percentages of EPA, DHA, and the omega-6 arachidonic acid (AA) were measured in RBCs at baseline and posttreatment in 122 participants with DSM-IV major depression who were randomly assigned between May 2005 and December 2008 to receive either 50 mg/d of sertraline and a daily dosage of 930 mg EPA/750 mg DHA or sertraline plus placebo. Associations between baseline omega-3 RBC levels and remission of depression (17-item Hamilton Depression Rating Scale score = 7) were analyzed by treatment arm. Results: Among participants in the omega-3 arm, baseline RBC levels of EPA + DHA (P = .002) and the EPA + DHA:AA ratio (P = .003) were significantly higher among those whose depression subsequently remitted compared with those whose depression did not remit. No associations were detected in the sertraline plus placebo arm. Baseline levels of EPA (P = .03) and the EPA + DHA:AA ratio (P = .04) moderated the relationship between treatment arm and depression outcomes. Conclusions: High baseline RBC levels of EPA and DHA and a high EPA + DHA:AA ratio predict favorable depression outcomes in patients receiving omega-3 supplements. Omega-3 supplementation may be an effective treatment for depression, but the requisite dosage and duration of treatment may depend on the patient's baseline level of omega-3 fatty acids.