> ...the current meta-analysis examines the effects of exercise on depressive symptoms in 58 randomized trials (n = 2982). An overall effect size of -0.80 indicates participants in the exercise treatment had significantly lower depression scores than those receiving the control treatment. This frac34; SD advantage represents level 1, Grade A evidence for the effects of exercise upon depression.
Link: http://www.ncbi.nlm.nih.gov/pubmed/19453207
From the abstract:
> ...the current meta-analysis examines the effects of exercise on depressive symptoms in 58 randomized trials (n = 2982). An overall effect size of -0.80 indicates participants in the exercise treatment had significantly lower depression scores than those receiving the control treatment. This frac34; SD advantage represents level 1, Grade A evidence for the effects of exercise upon depression.