Abstract
Previous research, including multiple meta-analytic investigations, has examined the potential benefits of omega-3 fatty acid supplementation for the treatment of depressive symptoms, though researchers have not consistently examined the potential moderating influence of co-morbid anxiety on treatment outcomes. The current meta-analysis was conducted to evaluate the effectiveness of omega-3 fatty acid supplementation for the treatment of major depressive disorder or dysthymia, with or without a comorbid anxiety diagnosis. Randomized, placebo controlled trials, without medical, psychiatric, neurological, or psychological comorbidities (with exception of co-morbid anxiety) were included. Nine studies (k = 15) were included with a total of 885 participants, 486 in treatment conditions (166 males, 320 females) and 399 in placebo conditions (121 males, 278 females), with an average age of 47.6 (12.4) in the treatment group and 47 (12) in the placebo group. Depression change was measured with established and validated depression measures. The overall effect size for reduction in depressive symptoms in the omega-3 treatment groups was relatively small relative to placebo-control groups (d = -.21, 95% CI = -.35, -.06). The only significant moderator was comorbidity status (Qb = 12.78, p = .002), with depression-only studies (i.e., those excluding co-morbid anxiety) resulting in a large effect size (d = -.82, 95% CI = -1.2, -.46) compared to studies allowing comorbid anxiety, which resulted in no effect (d = -.1, 95% CI = -.3, .06). Results highlight the importance of considering the moderating role of co-morbid anxiety when examining the potential effectiveness of omega-3 fatty acid supplementation for management of depression. Implications and suggestions are discussed.