A Cochrane review [Abstract] 1 included 39 studies with a total of 2326 participants. Twenty-three trials recruited participants from non-clinical populations with most involving recruitment of participants through the media. Thirty-three trials provided aerobic exercise. A total of 37 trials provided data for meta-analyses. For the 35 trials (n=1356) comparing exercise with no treatment or a control intervention, the pooled SMD for the primary outcome of depression at the end of treatment was -0.62 (95% CI -0.81 to -0.42), indicating a moderate clinical effect. When we included only the 6 trials (n=464) with adequate allocation concealment, intention-to-treat analysis and blinded outcome assessment, the pooled SMD for this outcome was not statistically significant (-0.18, 95% CI -0.47 to 0.11). Pooled data from 8 trials (n=377) providing long-term follow-up data on mood found a small effect in favour of exercise (SMD -0.33, 95% CI -0.63 to -0.03). Twenty-nine trials reported acceptability of treatment, 3 trials reported quality of life, none reported cost, and 6 reported adverse events. For acceptability of treatment (assessed by number of drop-outs during the intervention), the risk ratio was 1.00 (95% CI 0.97 to 1.04). Seven trials compared exercise with psychological therapy (n=189), and found no significant difference (SMD -0.03, 95% CI -0.32 to 0.26). Four trials (n = 300) compared exercise with pharmacological treatment and found no significant difference (SMD -0.11, -0.34, 0.12). One trial (n=18) reported that exercise was more effective than bright light therapy (MD -6.40, 95% CI -10.20 to -2.60).
Comment: The quality of evidence is downgraded by study quality (inadequate or unclear allocation concealment) and inconsistency (heterogeneity in interventions and outcomes).
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