Exercise is only good for your health, but it also can help you reduce depression. A recent study looked at exercise alone in treating mild to moderate depression. The researchers studied adults aged 20 to 45, finding that depressive symptoms were reduced almost 50 percent in individuals who participated in 30-minute aerobic exercise sessions three to five times a week.

The results, published in the January 2005 issue of the American Journal of Preventive Medicine, are comparable to results from studies in which patients with mild to moderate depression were treated with antidepressants or cognitive therapy.

“The effect you find using aerobic exercise alone in treating clinical depression is similar to what you find with antidepressant medications,” according to Dr. Trivedi, one of the study authors. “The key is the intensity of the exercise and continuing it for 30 to 35 minutes per day.”

The study included 80 people randomly placed into five groups. Two groups participated in moderately intense aerobics consistent with public health recommendations – one of those groups exercising three days a week and the other five days. Two other groups participated in lower-intensity aerobics for three days and five days per week. A fifth group did stretching flexibility exercises 15 to 20 minutes three days per week.

Individuals who participated in moderately intense aerobics experienced a decline in depressive symptoms by an average of 47 percent after 12 weeks. Those in the low-intensity exercise groups showed a 30 percent reduction in symptoms, while those in the last group averaged a 29 percent decline.

We don’t think of exercise as a treatment for depression, but this study and others suggest that it can have a powerful effect. Some experts estimate that only 23 percent of individuals with clinical depression seek treatment for the mental illness and only 10 percent receive adequate treatment. As many as 19 million Americans are thought to suffer from depressive disorders. Exercising regularly may help many of these people lift their depression.