Research output: Contribution to journal › Literature review
Depression is a common and important cause of morbidity and mortality worldwide. Depression is commonly treated with antidepressants and/or psychotherapy, but some people may prefer alternative approaches such as exercise. There are a number of theoretical reasons why exercise may improve depression. This is an update of an earlier review first published in 2009.
To determine the effectiveness of exercise in the treatment of depression. Our secondary outcomes included drop-outs from exercise and control groups, costs, quality of life and adverse events.
We searched the Cochrane Depression, Anxiety and Neurosis (CCDAN) Review Group's Specialised Register (CCDANCTR), CENTRAL, MEDLINE, EMBASE, Sports Discus and PsycINFO for eligible studies (to February 2010). We also searched www.controlledtrials.com in November 2010. The CCDAN Group searched its Specialised Register in June 2011 and potentially eligible trials were listed as 'awaiting assessment'.
Randomised controlled trials in which exercise was compared to standard treatment, no treatment or a placebo treatment in adults (aged 18 and over) with depression, as defined by trial authors. We excluded trials of postnatal depression.
Data collection and analysis
For this update, two review authors extracted data on outcomes at the end of the trial. We used these data to calculate effect sizes for each trial using Hedges' g method and a standardised mean difference (SMD) for the overall pooled effect, using a random-effects model. Where trials used a number of different tools to assess depression, we included the main outcome measure only in the meta-analysis. We systematically extracted data on adverse effects and two authors performed the 'Risk of bias' assessments.
Thirty-two trials (1858 participants) fulfilled our inclusion criteria, of which 30 provided data for meta-analyses. Randomisation was adequately concealed in 11 studies, 12 used intention-to-treat analyses and nine used blinded outcome assessors. For the 28 trials (1101 participants) comparing exercise with no treatment or a control intervention, at post-treatment analysis the pooled SMD was -0.67 (95% confidence interval (CI) -0.90 to -0.43), indicating a moderate clinical effect.
However, when we included only the four trials (326 participants) with adequate allocation concealment, intention-to-treat analysis and blinded outcome assessment, the pooled SMD was -0.31 (95% CI -0.63 to 0.01) indicating a small effect in favour of exercise. There was no difference in drop-outs between exercise and control groups. Pooled data from the seven trials (373 participants) that provided long-term follow-up data also found a small effect in favour of exercise (SMD -0.39, 95% CI -0.69 to -0.09). Of the six trials comparing exercise with cognitive behavioural therapy (152 participants), the effect of exercise was not significantly different from that of cognitive therapy. There were insufficient data to determine risks, costs and quality of life.
Five potentially eligible studies identified by the search of the CCDAN Specialised Register in 2011 are listed as 'awaiting classification' and will be included in the next update of this review.
Exercise seems to improve depressive symptoms in people with a diagnosis of depression when compared with no treatment or control intervention, however since analyses of methodologically robust trials show a much smaller effect in favour of exercise, some caution is required in interpreting these results.