Regular exercise may combat depression as effectively as antidepressants, say the results of a new study.

"Our findings suggest that a modest exercise program is an effective, robust treatment for patients with major depression who are positively inclined to participate in it," said lead author James A. Blumenthal, PhD, of the department of psychiatry and behavioral sciences at Duke University Medical Center in Durham, NC. "The benefits of exercise are likely to endure particularly among those who adopt it as a regular, ongoing life activity."

Dr. Blumenthal and colleagues gave approximately 150 study participants -- who were all 50 or older and diagnosed with depression -- one of three depression treatments for four months: exercise, the antidepressant known as Zoloft, or a combination of the two.

Those in the exercise group took three supervised classes per week at which they exercised on a treadmill or stationary bicycle at 70 to 85 percent of their maximum heart rate for 30 minutes. Those in the combination group performed the same exercise regimen in addition to taking Zoloft.

At the end of the four-month treatment period, all three groups exhibited similar results: significantly lower rates of depression.

To see how study participants who had experienced relief from depression were faring after the study ended, the researchers checked in with them again six months later.

The positive results from the exercise were maintained over the long term, the researchers found. Six months after the end of the study, those who had been in the exercise group had significantly lower depression relapse rates than those in the Zoloft or combination groups.

Dr. Blumenthal and colleagues speculated as to why the combination group had higher depression relapse rates than the exercise-alone group. "It is conceivable that the concurrent use of medication may undermine the psychological benefits of exercise by prioritizing an alternative, less self-confirming attribution for one's improved condition,"said Dr. Blumenthal.

The researchers explained that instead of incorporating the belief, "I was dedicated and worked hard with the exercise program; it wasn't easy, but I beat this depression,"patients might incorporate the belief, "I took an antidepressant and got better."

The researchers report their findings in the September/October issue of Psychosomatic Medicine.

The study results don't suggest exercise will work for every depressed person. The participants chose to volunteer in a study of exercise therapy for depression, therefore, they may have been particularly motivated to exercise and may have had strong faith that exercise could help them, Dr. Blumenthal and colleagues noted.

"The question remains whether the impressive results of this study will be applicable to the general population of middle-aged and older patients with major depressive disorder,"said Dr. Blumenthal.

"Exercise prescribed by a clinician may not be accepted and complied with to the same extent as when it is sought out and adopted on one's own," the researcher added.