(Reuters) - People with heart disease who are also depressed may get as much relief from their depression symptoms with regular exercise as with medication, according to a U.S. study.

Researchers writing in the Journal of the American College of Cardiology found that of 101 heart patients with signs of depression, those who exercised for 90 minutes per week and those who started taking Zoloft both improved significantly compared to participants assigned to drug-free placebo pills.

Pharmaceutical firm Pfizer supplied the Zoloft, known generically as sertraline, and placebos for the study, but researchers said the company was not involved with any other part of it.

Alan Rozanski, who wrote an editorial accompanying the study, said exercise can be thought of as another "potent tool on the shelf" to fight depression in heart patients.

"The attractiveness of exercise is that it has so many other physical benefits and it ought to be something very highly considered," said Rozanski, of St. Luke's and Roosevelt Hospitals in New York.

According to the study authors, up to 40 percent of heart patients have symptoms of depression, and depression itself has been linked to a higher risk of further heart trouble.

Past studies have produced mixed results on whether or not antidepressants or other established treatments may ease depression in heart patients, but there is a growing body of research that suggests exercise may help.

On Tuesday, researchers published a separate study of over 2,300 people with heart failure randomly assigned to exercise or usual care, which found the extra activity led to modest reductions in depression symptoms.

"We wanted to evaluate exercise and antidepressant medications in patients with heart disease and elevated depressive symptoms," said James Blumenthal, the lead researcher on both the current study and the earlier report.

Blumenthal, a clinical psychologist at Duke University medical Center in Durham, North Carolina, recruited 101 heart patients with depression between June 2006 and September 2010.

Those patients were separated into three groups. 37 went to supervised exercise sessions three times per week for a total of 90 minutes, 40 were given Zoloft and 24 took a placebo, with each intervention lasting four months.

The researchers analyzed participants' depression scores on a standard scale from 0 to 68, where 0 to 8 is considered normal and higher scores reflect more severe depression.

Before the start of treatment, each group's average score ranged from about 13.5 to 14.5.

Depression symptoms improved across the board over time, but participants in the exercise and medication groups saw a bigger benefit than those on the placebo.

Scores fell by 6.1 points in the Zoloft group, by 7.5 points among exercisers and by 4.5 points in the placebo group.

Exercisers were also less likely to be tired or report sexual problems than people on antidepressants, the researchers said.