Depression can spawn a spiral of lethargy and hopelessness, so that the last thing someone wants to do is exercise; but regular, moderate physical activity may lessen depression symptoms as much as some medications. Jeannine Stein, of the Los Angeles Times, reports.
When Gaetano Vaccaro meets depressed patients at Moonview Sanctuary, he sometimes moves part of the session outside, taking a walk while talking.
The result: "People's state of mind can shift."
"On its own, exercise does appear to have significant effects in terms of elevating mood," said Dr Andrew Leuchter, professor of psychiatry at the Semel Institute for Neuroscience and Human Behaviour, at the University of California.
Physical activity, he adds, is often used to augment treatments such as medication and cognitive behavioural therapy.
"If people are on medication or in treatment and haven't had a complete recovery from depression, exercise is useful in getting them all the way there."
Exercise affects the brain in several ways.
"People with depression tend to become somewhat inert, and they don't engage in their usual activities, and exercise gets people back to their usual level of activity," Dr Leuchter said. That can prompt an upward cycle, inspiring people to return to work and connect again with friends and family, ultimately providing motivation to stay on course.
Such connections are crucial.
"The psychological benefits make a big difference from my perspective," said James Blumenthal, professor of medical psychology at Duke University in Durham, North Carolina.
"People have a greater sense of being in control. They feel better about themselves and have more self-confidence."
A physical change can instigate a mental change, said Dr Vaccaro, director of development at Moonview Sanctuary, a psychological treatment centre in Santa Monica.
"When you're getting somebody to move and getting them to change a pattern in their life, just that little bit of pattern change can relate to a mood change, and they start to see themselves as a person who is active, not just a couch potato. They change their perception."
There may be direct physical effects on the brain as well. The treatment centre encourages exercise - yoga in particular - as a way to manage many types of mood disorder.
Besides having a strong mind-body connection, "yoga is something that can be modified to someone's activity level and is something they can do throughout their life," Dr Vaccaro said.
Several studies illustrate the benefits of exercise. In one, published in 2007 in the journal Psychosomatic Medicine, 202 men and women with major depression were randomly assigned to participate in a supervised exercise programme in a group setting, do home-based exercise, take an anti-depressant medication or take a placebo.
After 16 weeks, 41% were in remission, meaning they no longer had major depressive disorder.
Those who were in the exercise and medication groups tended to have higher remission rates than the placebo group. Another study examined how much cardiovascular exercise was needed to see a change in mood among those with mild to moderate cases of major depressive disorder.
The 80 men and women who took part in the research were randomly placed in four exercise groups that varied in the number of calories burned and the frequency of activity.
A placebo group did flexibility exercises three days a week. Those in the group that exercised at moderate intensity three to five days a week for about 40 minutes (consistent with public health recommendations) showed the biggest decrease in depressive symptoms compared with those who exercised less or just did stretching.
The 2005 study appeared in the American Journal of Preventive Medicine. Other pieces of the puzzle are missing.
Scientists are not sure what changes happen in the brain - and why - when people exercise. Many scientists and physicians believe exercise increases levels of serotonin, a neurotransmitter thought to be linked to mood regulation.
However, most of the studies supporting this have been done on animals. "It's hard to quantify it in humans for a number of reasons," Dr Leuchter said.
"We don't entirely understand exactly why patients get depressed in the first place. We have theories, but it's hard to know in individual cases. And we don't have a good way of looking at [changes] in the brain."
Scientists do know that exercise causes an increase in blood flow to the brain and raises the amount of energy the brain uses.
Even though the link between blood flow and mood isn't known, Dr Leuchter said, "the brain in general seems to be in a healthier state". Exercise may be key in fighting depression, but no generic prescription fits everyone.
Overall health and exercise history factor into what kind of regimen might be prescribed. "If someone was a runner, I'd get them back to running," Dr Leuchter said.
"If not, I'm not going to have the goal of turning someone into a major athlete. I'd simply want to get them active, and even walking around the block might be good."
Those who are not currently in treatment for depression should consult a physician before exercising, to make sure they have no underlying health problems.
Patients who are on medication or in therapy for depression should not consider exercise a substitute for either treatment. "The key," Prof Blumenthal said, "is really maintenance. You have to do it on an ongoing basis. You should find something you enjoy, but doing something is better than nothing."