In a 2005 study presented in the American Journal of Preventive Medicine, researchers found that aerobic exercise, at the level suggested for public health, reduced depression as measured by the Hamilton Rating Scale for Depression by 47% over 12 weeks.  The public health suggested level was defined as 17.5 kcal/kg/week (5 days a week).  The low dose level, 7.5 kcal/kg/week (3 days a week) was no more statistically significant than placebo.

Researchers concluded that aerobic exercise at public health recommended levels is an effective treatment for mild to moderate depression.