Researchers are starting to address this question, however. Recently, Madhukar Trivedi, MD, a psychiatrist at the University of Texas Southwestern Medical College, and colleagues studied exercise as a secondary treatment for patients with major depressive disorder who hadn't achieved remission through drugs alone. They evaluated two exercise doses: One group of patients burned four kilocalories per kilogram each week, while another burned 16 kilocalories per kilogram weekly. They found both exercise protocols led to significant improvements, though the higher-dose exercise program was more effective for most patients (Journal of Clinical Psychiatry, 2011).
The study also raised some intriguing questions, however. In men and women without family history of mental illness, as well as men with family history of mental illness, the higher-dose exercise treatment proved more effective. But among women with a family history of mental illness, the lower exercise dose actually appeared more beneficial. Family history and gender are moderating factors that need to be further explored, the researchers concluded.
Questions also remain about which type of exercise is most helpful. Most studies have focused on aerobic exercise, though some research suggests weight training might also be effective, Smits says. Then there's the realm of mind-body exercises like yoga, which have been practiced for centuries but have yet to be thoroughly studied. "There's potential there, but it's too early to get excited," he says.