Individuals who participated in moderately intense aerobics three to five days per week experienced a decline in depressive symptoms by an average of 47 percent after 12 weeks.

Intensity of Exercise Is Important

The results, published in the January 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, said Dr. Madhukar Trivedi, professor of psychiatry and director of UT Southwestern's mood disorders research program.

"The effect you find using aerobic exercise alone in treating clinical depression is similar to what you find with antidepressant medications," said Dr. Trivedi, a study author and holder of the Lydia Bryant Test Professorship in Psychiatric Research. "The key is the intensity of the exercise and continuing it for 30 to 35 minutes per day. It's not for the faint of heart."

Stretching Exercises Also Help

The study, conducted between July 1998 and October 2001, included 80 people randomly placed into five groups. Two groups participated in moderately intense aerobics consistent with public health recommendations; one of those groups exercised three days a week and the other five days.

Another two groups participated in lower-intensity aerobics for three days and five days per week, and a fifth group did stretching flexibility exercises 15 to 20 minutes three days per week. Exercise programs included supervised instruction at the Cooper Institute in Dallas.

Individuals who participated in moderately intense aerobics, such as exercising on a treadmill or stationary bicycle -- whether it was for three or five days per week -- 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.

Alternative for Those Who Don't Seek Treatment

"Numerous effective treatments for depression are available, yet many people don't seek treatment because of the negative social stigma still associated with the disease," Dr. Trivedi said. "Exercise may offer a viable treatment alternative, particularly as it can be recommended for most individuals."

Experts estimate that only 23 percent of individuals with clinical depression seek treatment for the mental illness and only 10 percent receive adequate treatment. Almost 19 million Americans are thought to suffer from depressive disorders.