NEW YORK (Reuters Health) - Exercise appears to have little long-term impact on depression, according to a new review of large studies investigating the relationship.

As long as people with depression were taking part in an exercise program, it appeared to have a small effect on their symptoms - but months after the intervention ended, they were just as depressed as people who did not participate in the exercise program.

Study author Dr. Jesper Krogh at Bispebjerg University Hospital in Denmark told Reuters Health he was surprised to see exercise had no long-term impact on depression. “I expected that patients that had benefited from the intervention would stay well,” he said.

Overall, “the effect on depression is at best small, if any,” he noted.

However, this does not mean that exercise is not at all helpful to people who are depressed. People with depression are also at a higher risk of dying from heart disease and diabetes, and for these conditions, there is “solid documentation” that supports the benefits of exercise. “Therefore, exercise is important in this population,” Krogh said.

An estimated 17 percent of people living in Western countries develop depression at some point in their lives.

Previous research has suggested that exercise could have an impact on depression, at least in the short term. In a 2007 study of 202 depressed adults, investigators found that those who went through group-based exercise therapy did as well as those treated with an antidepressant drug. That same year, another small study found that regular exercise improved depression symptoms in people who’ve failed to get better with antidepressant medication.

The current study, in contrast, looked at data collected from only large studies, some of which measured exercise’s long-term impact by following patients for months after the intervention concluded.

The analysis, published in the Journal of Clinical Psychiatry, is based on 13 studies including nearly 700 patients, half of whom were randomly assigned an exercise intervention to help with their depression.

On average, people appeared to have improved slightly by the end of the exercise intervention, relative to people who did not exercise.

However, according to the 5 studies that followed patients for between 6 and 26 months, the benefits of physical activity did not appear to last once the program ended. “If exercise was a pill, I do not think the FDA (Food and Drug Administration) would approve it as an antidepressant,” he said.

Perhaps, Krogh suggested in an e-mail, exercise itself has indirect effects on depression that only last while people are doing it. “Maybe the effect of the intervention is not related to the physical exercise but to an element of structure in the daily lives of depressed patients,” Krogh noted. Some of the benefits, he noted, may include “meeting at regular intervals with other patients and staff that know the hassles of living with depression.”

SOURCE: link.reuters.com/qyt93q Journal of Clinical Psychiatry, online October 19, 2010.